POPULATION DYNAMICS, MOVEMENTS, AND SPAWNING HABITAT OF THE

SHORTNOSE STURGEON, Acipenser brevirostrum, IN THE ALTAMAHA RIVER

SYSTEM, GEORGIA

by

ROBERT JASON DEVRIES

(Under the Direction of Douglas L. Peterson)

ABSTRACT

In Georgia, the Altamaha River supports what is believed to be one of the largest

remaining shortnose sturgeon populations south of Chesapeake Bay, however the

current status and recent population trends of this population are unknown. A

population estimate for shortnose sturgeon in the Altamaha River was generated using

POPAN within Program MARK. Annuli on pectoral fin rays were used to determine age.

Mortality estimates were calculated from catch curves. Radio telemetry was used to

monitor movements and habitat use of 12 adult shortnose sturgeon. The results of this

study indicate a population size of 6320 (95% C.I. 4387-9249) with a disproportionate

number of juveniles. Ages ranged from 4 to 14 yr. Estimated annual mortality ranged

between 29-34%. Spawning runs initiated in late December and were long, single-step

migrations. Juveniles and adults coinhabited summer habitat in deep riverine stretches

and appeared confined to freshwater when water temperatures exceeded 27 oC.

INDEX WORDS: Shortnose sturgeon, Acipenser brevirostrum, Abundance estimate,

Population dynamics, Migration, Habitat, Radio telemetry, Altamaha River

POPULATION DYNAMICS, MOVEMENTS, AND SPAWNING HABITAT OF THE

SHORTNOSE STURGEON, Acipenser brevirostrum, IN THE ALTAMAHA RIVER

SYSTEM, GEORGIA

by

ROBERT JASON DEVRIES

B.S., College of Charleston, 1998

A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial

Fulfillment of the Requirements for the Degree

MASTER OF SCIENCE

ATHENS, GEORGIA

2006

© 2006

Robert Jason DeVries

All Rights Reserved

POPULATION DYNAMICS, MOVEMENTS, AND SPAWNING HABITAT OF THE

SHORTNOSE STURGEON, Acipenser brevirostrum, IN THE ALTAMAHA RIVER

SYSTEM, GEORGIA

by

ROBERT JASON DEVRIES

Major Professor: Douglas L. Peterson

Committee: Cecil A. Jennings Steven B. Castleberry

Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2006

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Douglas Peterson for his guidance and support.

I would also like to thank the other members of my committee, Drs. Cecil Jennings and

Steven Castleberry.

Special thanks also go to David Higginbotham, for his help with logistics and

statistics; Drs. James Peterson and Michael Conroy, for their help and input for the

population estimation; to Paul Schueller and Jason Meador for their help with GIS; and

to Brian White, Clay Fordham, and the host of technicians who assisted me during the

course of this study.

I would also like to extend my gratitude to the Georgia Department of Natural

Resources and Gordon Rogers for their input and expertise throughout this project.

Funding was provided by the National Marine Fisheries Service.

iv

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ...............................................................................................iv

LIST OF TABLES...........................................................................................................vii

LIST OF FIGURES..........................................................................................................ix

CHAPTER

1 INTRODUCTION AND LITERATURE REVIEW............................................. 1

Taxonomy and Systematics....................................................................... 1

Morphology ................................................................................................ 3

Genetics..................................................................................................... 6

Life History................................................................................................. 8

Habitat and Movements ........................................................................... 14

Distribution and Legal Status ................................................................... 16

Mechanisms Leading to Declines ............................................................ 16

Management Approaches........................................................................ 20

Research Objectives and Justification ..................................................... 21

2 STUDY AREA AND METHODS .................................................................. 24

Study Area ............................................................................................... 24

Materials and Methods............................................................................. 26

Abundance Estimates ............................................................................. 28

Population Age Structure ......................................................................... 29

v

Identification of Critical Habitat for Shortnose Sturgeons......................... 33

3 RESULTS.................................................................................................... 37

Abundance Estimates.............................................................................. 37

Population Age Structure ......................................................................... 42

Habitat and Seasonal Movements ........................................................... 56

4 DISCUSSION .............................................................................................. 62

Abundance Estimates.............................................................................. 62

Population Age Structure ......................................................................... 63

Habitat and Seasonal Movements ........................................................... 71

Management Implications ........................................................................ 75

Summary ................................................................................................. 76

LITERATURE CITED .................................................................................................... 78

vi

LIST OF TABLES

Page

Table 3.1. Trammel net and gill net capture comparison in 2004 and

2005. Trammel nets were constructed from an inner panel of

7.6 cm and 2 outer panels of 30.5 cm stretched mesh. Gill nets

were constructed from 10.2 and 15.2 cm stretched mesh.

Experimental gill nets were constructed from 7.6, 10.2, and

15.2 cm stretched mesh ............................................................................. 39

Table 3.2. Estimates of shortnose sturgeon abundance in the Altamaha

River, Georgia ............................................................................................ 41

Table 3.3. Age-frequency key for shortnose sturgeon captured in the Altamaha

River system in 2004. Ages were determined from the first pectoral

fin ray. The ages from each individual subsample were applied

proportionally across the same length-group. Note: age-2

or age-13 individuals were not obtained during this study .......................... 48

Table 3.4. Age-frequency key for shortnose sturgeon captured in the Altamaha

River system in 2005. Ages were determined from the first pectoral

fin ray. The ages from each individual subsample were applied

proportionally across the same length-group. Note: age-2

or age-13 individuals were not obtained during this study .......................... 49

vii

Table 3.5. Radio tagged shortnose sturgeon release dates and number of

relocations in the Altamaha River, Georgia. The * denotes an

individual tag that did not change locations after an initial ~100 km

upstream migration after tag implantation. ** indicates a censored

individual after x days at large .................................................................... 59

Table 4.1 Coefficient of variance (CV) of age estimates for between-observer

precision for reported long-lived species .................................................... 65

viii

LIST OF FIGURES

Page

Figure 1.1. Lateral view illustrations of two adult shortnose

sturgeon, Acipenser brevirostrum (Illustrations by Paul Vecsei)................... 2

Figure 1.2. Head and mouth variations of adult shortnose sturgeon,

Acipenser brevirostrum. (Illustrations by Paul Vecsei).................................. 5

Figure 2.1. The Altamaha River watershed (gray) including the headwater

tributaries, the Ocmulgee and Oconee Rivers with impoundments ............ 25

Figure 2.2. Shortnose sturgeon capture sites in the tidally influenced

lower 40 rkm of the Altamaha River (sampling sites are denoted by o)...... 27

Figure 2.3. Altamaha River basin covered on a weekly basis by boat equipped

with a scanning receiver and loop antenna ................................................ 36

Figure 3.1. Size distributions of captured shortnose sturgeon from the

Altamaha River, Georgia in 2004 (top) and 2005 (bottom). In 2004,

individuals were caught in 10.2 and 15.2 cm gill nets and trammel

nets. In 2005, gill nets were replaced with experimental gill nets

constructed from 7.6, 10.2, and 15.2 cm panels......................................... 38

Figure 3.2. Monthly catch per unit effort (CPUE) of shortnose sturgeon

in the Altamaha River in 2004 and 2005. (Sampling not conducted

ix

during months denoted with an asterisk.) ................................................... 40

Figure 3.3. Nominal age frequency of shortnose sturgeon captured in the

Altamaha River, Georgia in 2005. Ages of individual fish were

determined from pectoral fin ray sections and interpreted by 3

independent observers period 1 ................................................................. 44

Figure 3.4. Age-bias graph for 2 interpreters of sampled fin rays from Altamaha

River shortnose sturgeon. The dashed line designates the 1:1

ratio line. Age estimation bias is present ................................................... 46

Figure 3.5. Growth of shortnose sturgeon (both sexes) in the Altamaha River,

Ogeechee River, and Hudson River ........................................................... 47

Figure 3.6. Weight – length relationship of shortnose sturgeon (both sexes)

from the Altamaha River, Georgia .............................................................. 48

Figure 3.7. 2004 uncorrected catch curve for ages 4 – 12 of Altamaha River

shortnose sturgeon..................................................................................... 51

Figure 3.8. 2005 uncorrected catch curve for ages 4 – 12 of Altamaha River

shortnose sturgeon..................................................................................... 52

Figure 3.9. Size composition of shortnose sturgeon captured in trammel

nets and gill nets from the Altamaha River, Georgia in 2004.

Catch per unit effort is the number of shortnose sturgeon captured

per net per slack tide .................................................................................. 52

x

Figure 3.10. Size composition of shortnose sturgeon captured in trammel nets

and experimental gill nets (constructed from 7.6, 10.2, and 15.2 cm

stretched mesh) from the Altamaha River, Georgia in 2004. Catch

per unit effort is the number of shortnose sturgeon captured per net

per slack tide .............................................................................................. 53

Figure 3.11. Indirect selectivity of trammel nets, 10.2 cm, and 15.2 cm

stretched mesh gill nets from the Altamaha River, Georgia in 2004........... 54

Figure 3.12. Indirect selectivity of trammel nets, and experimental gill nets

composed of 7.6, 10.2, and 15.2 stretched mesh panels from the

Altamaha River, Georgia in 2005) .............................................................. 55

Figure 3.13. Confirmed and suspected spawning areas of shortnose sturgeon in

the Altamaha River, GA (2005)................................................................... 60

Figure 3.14. Non-spawning habitat of shortnose sturgeon in the Altamaha River, GA

(April-December 2005) ............................................................................... 61

xi

CHAPTER 1

INTRODUCTION AND LITERATURE REVIEW

The family Acipenseridae is composed of 27 species dispersed among 4 genera with

a life history characterized by a long life span, delayed maturity, and protracted

spawning periodicity (Artyukhin 1995, Bemis and Kynard 1997, Billard and Lecointre

2001). The shortnose sturgeon (Acipenser brevirostrum) (Figure 1.1) is the smallest

species within this family. Although no historically large populations have been

described, shortnose sturgeon were nevertheless exploited along with the sympatric

Atlantic sturgeon (Acipenser oxyrinchus) (LeSueur 1818, Smith et al. 1984). Shortnose

sturgeon became sufficiently scarce that they were declared an endangered species in

the United States in 1967, and are considered a species of special concern in Canada

(Dadswell et al. 1984, COSEWIC 2005). Today, few healthy populations exist and

many anthropogenic factors continue to impede restoration efforts (Kynard 1997).

Hydroelectric dams are perhaps the most significant limiting factor because they

obstruct access to spawning grounds and alter many critical habitats (Auer 1996,

Kynard 1997).

Taxonomy and Systematics

The earliest known appearance of acipenserids within the fossil record dates to the

Upper Cretaceous with possible ancestors originating during the Lower Jurassic, some

Figure 1.1. Lateral view illustrations of two adult shortnose sturgeon, Acipenser

brevirostrum. (Illustrations by Paul Vecsei)

2

200 million years ago (Gardiner 1984, Findeis 1997, Bemis and Kynard 1997,

Choudhury and Dick 1998). Though many aspects of sturgeon phylogeny remain

uncertain (Artyukhin 1995), most taxonomists have categorized the genus Acipenser as

monophyletic (Bemis et al. 1997), although recent studies have disputed the validity of

this classification (Birstein et al. 1997, Choudhury and Dick 1998, Birstein et al. 2002).

More recently, genetic analyses have been used to further refine phylogeny as well as

taxonomy within the Acipenseriformes. The shortnose sturgeon has been of particular

interest because of its unique 16N ploidy, which has given rise to conflicting theories

regarding the relationships and phylogeny of the order. Contrary to Birstein et al.

(1997), who considered shortnose sturgeon a young species, Choudhury and Dick

(1998) regarded the shortnose sturgeon as ancestral to all interior eastern North

American acipenserids resulting from glacially induced isolation. Further complicating

these phylogenetic arguments, Artyukhin (1995), Choudhury and Dick (1998), and

Krieger et al. (2000) suggested that the shortnose sturgeon and the lake sturgeon (A.

fulvescens) are sister species. Regardless of which of these arguments are correct,

researchers agree that acipenserids are an ancient group and that surviving lineages

are best explained by more recent geological and climatic changes (Choudhury and

Dick 1998). However, determining actual relationships among species will continue to

be problematic for years to come.

Morphology

Acipenserids are distinctive in morphology with characteristics such as trunk

armoring scutes, a ventral mouth, rostral chemosensory barbels, spiral valve intestine,

3

and a swim bladder that has retained some of the lung-like characteristics of early

actinopterigeans (Dadswell et al. 1984). The shortnose sturgeon is distinguished from

other North American sturgeons by a wide mouth, absence of a fontanelle, nearly

complete absence of postdorsal scutes, and preanal scutes often arranged in a single

row (Scott and Crossman 1973, Dadswell et al. 1984). Dorsal, lateral, and ventral scute

counts vary from 7-13, 21-33, and 6-11, respectively. Dorsal fin rays number 38-42 and

anal fin rays number 19-22 (Scott and Crossman 1973, Dadswell et al. 1984). The

rostrum is disproportionately large in juveniles, exceeding postorbital distance in

individuals <39 cm FL, gradually decreasing as individuals age (Vladykov and Greeley

1963). Shortnose sturgeon have a large, transverse mouth averaging 74% of

interorbital width (Vladykov and Greeley 1963). Mouth shape and size is similar to that

of lake sturgeon (A. fulvescens) and is a prominent characteristic used to distinguish the

shortnose sturgeon from the sympatric Atlantic sturgeon (A. oxyrinchus) (Figure 1.2)

(see Vladykov and Greeley 1963, Dadswell et al. 1984). Barbels are situated closer to

the tip of the snout than to the mouth. Gill rakers are long and triangular, usually

numbering 22-29 on the first branchial arch (Vladykov and Greeley 1963, Scott and

Crossman 1973).

Body armoring is extensive in shortnose sturgeon, although weakly developed in

adults compared to that of other North American sturgeons (Vladykov and Greeley

1963, Dadswell et al. 1984). Sharp, apical hooks are prominent on scutes of juveniles

but are gradually lost as adults. The body lacks scales, and adults are generally

smooth-skinned. Body coloration is typically dark brown along the dorsal surface,

4

Figure 1.2. Head and mouth variations of adult shortnose sturgeon, Acipenser

brevirostrum. (Illustrations by Paul Vecsei)

5

becoming a yellowish-brown laterally, and white or cream colored ventrally. Scutes are

uniformly colored and are much lighter than the surrounding dorsal and lateral tissue.

Scott and Crossman (1973) and Dadswell et al. (1984) noted that juveniles exhibited

black blotches over much their body, although this has not been observed in juveniles of

similar size observed from the Altamaha River.

Genetics

Polyploidy is currently thought to have had an important role in the evolution of the

Acipenseriformes (Blacklidge and Bidwell 1993, Ludwig et al. 2001). All acipenserids

can be genetically categorized into one of two groups: those with 112-120

chromosomes, those with 240-250, and those with more than 250 (Blacklidge and

Bidwell 1993, Birstein et al. 1997, Fontana et al. 1999, Kim 2004). Within the

acipenserids, the shortnose sturgeon and the Sakhalin sturgeon (A. mikadoi) are the

only two known allopolyploids, having derived from 2 different ancestral species

(Birstein et al. 1997). There currently is much debate on the specific ploidy number of

shortnose sturgeons. Blacklidge and Bidwell (1993) categorized shortnose sturgeons

as dodecaploid (12N), and proposed that this species originally derived from the

hybridization between 4N and 8N species. Birstein et al. (1997) however, proposed that

shortnose sturgeons were instead 16N because allopolyploidy was unknown in other

sturgeon species. Ludwig et al. (2001) and Kim et al. (2005) disputed both these

theories, with the former proposing that shortnose sturgeons were instead octoploids.

Kim et al. (2005) however agreed with Blacklidge and Bidwell (1993) that the number of

chromosomes possessed by shortnose sturgeon (362-372) was actually far less than

6

the 500 proposed by Birstein et al. (1997). Blacklidge and Bidwell (1993) also argued

that the number of chromosomes was more indicative of dodecaploidy. Regardless of

whether the chromosomal number is 500 or the more probable ~360, the shortnose and

Sakhalin sturgeons have among the highest number of chromosomes yet reported for

any vertebrate (Birstein et al. 1997).

Recent genetic studies also have attempted to explain shortnose sturgeon

population stock structures. Wirgin et al. (2005) found that southern populations

displayed genetic differences among rivers and argued that this could be explained by

relatively small population sizes and their inherent susceptibility to stochastic drift. The

large degree of genetic variation among southern rivers also may be explained by lack

of influence of Pleistocene glaciation. Recolonization of northern rivers would have

occurred over the past 10,000 years and genetic differentiation would not be as

pronounced as in southern rivers (Wirgin et al. 2005). This pronounced difference in

genetic stock structure among populations, particularly in southern rivers, indicates

minimal gene flow among populations and genetic similarities may actually be indicative

of environmental similarities (Quattro et al. 2002, Waldman et al. 2002). Gene flow,

however, may be a function of population size rather than adjacent river proximity. For

example, Kynard (1997) and Walsh et al. (2001) argued that the Hudson River was a

possible source of individuals to other regional rivers because of its large population

size.

7

Life History

The first studies focusing on shortnose sturgeon were conducted until the late

nineteenth-early twentieth century. These studies were initiated primarily to investigate

aquacultural techniques (Ryder 1890, Meehan 1910). More recent studies have

focused primarily on life history, population dynamics, and habitat utilization. These

studies have primarily originated in the northern extent of the range, where several large

populations now exist as a result of conservation and recovery efforts (Dadswell 1979,

Pekovitch 1979, Taubert and Dadswell 1980, Hastings et al. 1987, Hoff et al. 1988, Bain

et al. 1995, Kynard et al. 2000, Secor and Woodland 2005). Studies of southern stocks

have revealed a slightly different life history pattern in terms of spawning periodicity and

migrational patterns (Heidt and Gilbert 1978, Marchette and Smiley 1982, Hall et al.

1991, Collins and Smith 1993).

Eggs

Shortnose sturgeon eggs are darkly colored, usually dark brown, black, or olive

gray (Meehan 1910, Dadswell 1979, Hoff, 1988, Kynard 1997). Egg diameter is

typically 3.00-3.20 mm (Dadswell 1979) and does not change after fertilization or

immersion in water (Buckley and Kynard 1981, Dadswell et al. 1984). Fecundity

estimates range from 76,000 to 95,200, but averages 11,600 eggs per kg of fish (Heidt

and Gilbert 1978, Dadswell 1979, COSEWIC 2005). Eggs are not adhesive when first

spawned. Special protuberances on the egg membrane that maximize surface area

available for attachment develop within a few minutes after water exposure (Meehan

1910, Markov 1978, Dadswell et al. 1984). Development of fertilized eggs is directly

8

related to water temperature (Wang et al. 1985, Hardy and Litvak 2004). Meehan

(1910) found that eggs in water temperatures of 8-12 oC hatched 13 days after

fertilization—however incubation time was reduced to 8 days at 17 oC (Buckley and

Kynard 1981).

Yolk-sac larvae

At hatching, yolk-sac larvae are between 7-11 mm TL. Larvae are dark gray, with a

large, slightly pigmented yolk-sac, unpigmented eyes, undeveloped fins and an unopen

mouth (Meehan 1910, Taubert 1980a, Taubert and Dadswell 1980, Buckley and Kynard

1981, Dadswell et al. 1984, Bain 1997). They are benthic and photonegative, often

forming dense aggregations with other larvae when hiding (Buckley and Kynard 1981,

Dadswell et al. 1984, Richmond and Kynard 1995, Bain 1997). Dorsal and lateral

pigmentation is well developed by 15 mm TL and is most pronounced in the caudal

region (Taubert and Dadswell 1980).

The spiral valve is discernable in individuals ≤11.6 mm and rudimentary gill

structures are visible on specimens ≤9.5 mm TL (Bath et al.1981). At hatching, the

mouth is merely a small indentation, but begins to develop at 8.4 mm TL and small,

unicuspate teeth are present by 15 mm TL (Bath et al.1981, Taubert and Dadswell

1980, Richmond and Kynard 1995). Barbels first appear as tiny buds at 9.7 mm TL, but

are well developed by 15 mm TL (Bath et al.1981, Taubert and Dadswell 1980). The

eyes, fin buds, gills, and lateral line are either undeveloped or poorly developed in newly

hatched yolk-sac larvae, but are well defined by 15 mm TL (Bath et al.1981, Taubert

and Dadswell 1980, Richmond and Kynard 1995).

9

Post yolk-sac larvae

The larval stage begins with initiation of active feeding. Active feeding of larval

shortnose sturgeon begins with the depletion of the yolk, which typically occurs after 12

days, or at 15 mm TL at 15-17 oC (Taubert and Dadswell 1980, Bath et al.1981, Buckley

and Kynard 1981, Kynard 1997). The finfold increases with size, gradually separating

into the median fins, dorsal and anal fin ray basal supports, and dorsal and anal scutes

(Bath et al.1981). Spiracles, dermal ossification and scutes as well as fin rays, which

were absent earlier, begin to develop at 18-19 mm TL (Bath et al.1981, Gilbert 1989).

Larvae become photopositive after yolk sac depletion and can become lighter or darker

in response to changes in light intensity (Buckley and Kynard 1981, Richmond and

Kynard 1995, Kynard and Horgan 2002). The duration of downstream drift by larval

shortnose sturgeon is brief, usually about 2 days, and typically occurs at about 20 mm

TL (Richmond and Kynard 1995, Bain 1997). Richmond and Kynard (1995) postulated

that downstream movements of larvae serve to help disperse larvae from spawning

grounds and to help them find suitable cover.

Larvae larger than 15 mm TL are active swimmers, but are only capable of short

bursts of movement. At this stage most individuals are associated with the deepest

water available (Taubert and Dadswell 1980, Bath et al. 1981, Hoff et al. 1988, Dovel et

al 1989, Richmond and Kynard 1995, Kynard and Horgan 2002). Swimming activity

increases after 9-14 days (14-17 mm TL), possibly signifying that individuals would be

migrating from the spawning areas (Richmond and Kynard 1995). This movement is

most likely nocturnal to take advantage of low light levels and the increased cryptic

coloration of the larvae (Buckley and Kynard 1981, Richmond and Kynard 1995).

10

Juveniles

Juveniles are morphologically similar to adults, possessing a full complement of

rayed fins. At the onset of the juvenile stage, the tooth-filled mouth becomes toothless

and protrusible (Richmond and Kynard 1995). The scutes, which are sharply tipped as

juveniles, are maintained throughout the life of the sturgeon, demonstrating the

relationship between the need for body armoring and the presence of large predators.

As juveniles, the only confirmed predator of shortnose sturgeons is the yellow perch,

Perca flavescens (Dadswell et al. 1984). In southern populations alligators (Alligator

mississippiensis), sharks, or other fishes (e.g. catfish) also may be potential predators;

however, predation on adult shortnose sturgeon has not been documented (Scott and

Crossman 1973, Gilbert 1989).

Metamorphosis into the juvenile stage is complete by 31.5 mm TL. The juvenile

stage continues until the fish matures after 3-10 years (Gilbert 1989, Richmond and

Kynard 1995). Immature individuals remain primarily within river channels and

commonly feed on aquatic insects, isopods, and amphipods (Dadswell 1979, Carlson

and Simpson 1987, Bain 1997). Downstream migration continues throughout the first

year and individuals age 1 and older utilize the same habitats as adults (Dovel et al.

1989, Kynard 1997). Juveniles older than 1 year also make seasonal migrations,

moving upriver during warmer months where they shelter in deep holes, before

returning to the fresh/salt water interface when temperatures cool (Flournoy et al. 1992,

Collins et al. 2002a).

11

Adults

Although adult shortnose sturgeon may attain maximum lengths of 143 cm TL and

weights greater than 20 kg, they rarely exceed 122 cm TL (Dadswell 1979, Gilbert

1989). However, maximum size varies with latitude with southern individuals attaining

smaller maximum sizes (Dadswell 1979, Gilbert 1989). Growth rates and maximum

ages also are thought to vary with latitude. Dadswell et al. (1984) and Heidt and Gilbert

(1978) both assert that southern stocks grow faster and reach maturity earlier than do

their northern counterparts. Contrary to the 67-year old shortnose sturgeon captured in

the Saint John River, Canada by Dadswell (1979), the oldest reported individual from a

southern population was 14 years old and measured 98.5 cm FL in the Ogeechee

River, Georgia (Fleming et al. 2003).

Adult shortnose sturgeon also exhibit a latitudinal gradient relative to age of

maturation, spawning time, and migratory behavior (Dadswell et al. 1984, Gilbert 1989,

Rogers and Weber 1994). In Georgia waters, male sturgeon are thought to mature at 2-

3 years while females mature by age-6 (Dadswell et al. 1984, Kynard 1997). In more

northerly populations, such as the St. John River population, males may mature at 10-

11 years of age and females at age 12-18 (Dadswell et al. 1984, Bain 1997, Kynard

1997).

Feeding Behavior

The shortnose sturgeon is a benthic invertivore that finds prey by using its barbels as

tactile receptors and vacuuming either the substrate or plant surfaces with its

protuberant mouth (Dadswell et al. 1984, Gilbert 1989). Juveniles feed indiscriminately,

12

often ingesting large amounts of mud, stones, and plant material along with prey items

(Curran and Ried 1937, Dadswell 1979, Carlson and Simpson 1987). Several studies

have documented juveniles with up to 90% of the gut content containing non-food

material (Curran and Ries 1937, Dadswell 1979, Marchette and Smiley 1982). The diet

of juveniles includes small insects and cladocerans (Dadswell 1979, Marchette and

Smiley 1982, Dadswell et al. 1984, Carlson and Simpson 1987, Gilbert 1989). Adults

also appear to feed indiscriminately, but may be more capable of separating food and

non-food material prior to ingesting, depending on substrate (Dadswell 1979, Dadswell

et al. 1984, Gilbert 1989). Studies of gut contents show that the diet of adult shortnose

sturgeon typically consists of small bivalves, gastropods, polychaetes, and even small

benthic fish (McCleave et al. 1977, Dadswell 1979, Marchette and Smiley 1982,

Dadswell et al. 1984, Gilbert 1989, Moser and Ross 1995, Kynard et al. 2000).

Adult shortnose sturgeon feed throughout the year; however, Dadswell (1979) found

that females ceased feeding nearly eight months before spawning. Conversely, males

continue to feed throughout the fall and winter as long as they are located in saline

waters (Dadswell et al. 1984). Dadswell (1979) also documented individuals of both

sexes actively feeding immediately after spawning. Feeding occurs primarily at night in

water 1-5 m deep, although depth is directly related to temperature with feeding

occurring deeper during warmer months (Dadswell et al. 1984, Gilbert 1989).

13

Habitat and Movements

Habitat

Shortnose sturgeon use several distinct habitats throughout their life cycle with each

stage of development requiring a specific habitat. Adult and juvenile habitats differ

depending on seasonal and stochastic variables. Seasonal changes in habitat have

been well documented, but vary with latitude (Kynard et al. 2000). In northern

populations, both juveniles and non-spawning adults use deep segments of rivers, often

deeper than 10 m, during fall and winter months. In warmer months, they forage widely

throughout the river and estuary (Dadswell 1979, Hastings et al. 1987, Geoghegan et al.

1989, O’Herron et al. 1993, Kynard et al. 2000, Welsh et al. 2001). In southern

populations, individuals take refuge in deep, freshwater habitat during the summer,

rarely moving from them, and forage widely throughout the estuary during winter

months (Collins and Smith 1993, Rogers and Weber 1994, Weber et al. 1998). Small

juveniles, however, are much less tolerant of salinity and grow more slowly in a saline

environment and therefore remain primarily within freshwater habitats (Jenkins et al.

1993, Jarvis et al. 2001).

Shortnose sturgeon can be found over a variety of substrates, but probably select

areas based on food availability and thermal tolerances (Crance 1986). Riverine

habitats often are characterized by sandy-mud substrates, although shortnose sturgeon

do not avoid vegetated areas as evidenced by the presence of ingested plant material

likely consumed while foraging for gastropods (Dadswell 1979, Marchette and Smiley

1982). Specific data on the thermal preferences of shortnose sturgeon is limited, the

best data relating only to spawning adults and small juveniles.

14

Migrational Behavior

Shortnose sturgeon display both random and non-random movements (Dadswell et

al. 1984, Buckley and Kynard 1985). Although some populations are known to remain

within the tidally influenced portions of their home rivers, only Taubert (1980b)

described a population home range. Populations with access to the sea roam freely

throughout estuarine and riverine environments although these movements are often

dictated by temperature (Gilbert 1989). As water temperatures increase during

summer, individuals typically move upstream and remain near the fresh-salt water

interface until temperatures begin to fall (Dadswell et al. 1984, Buckley and Kynard

1985, Rogers and Weber 1994, Weber 1996, Collins and Smith 1997, Palmer 2001).

All sturgeon species undertake some type of spawning migration (either in the form

of anadromy or potomodromy), and all spawn in freshwater (Auer 1996, Fontana et al.

2001). Upstream migrations usually are associated with spawning behavior, while

downstream migrations normally are associated with feeding behavior (Bemis and

Kynard 1997). Gerbilskiy (1957) and Bemis and Kynard (1997) described spawning

migrations as either “one-step” or “two-step” movement patterns; the former typified by

a long, uninterrupted spring migration followed immediately by spawning; the latter

characterized by an abbreviated fall migration followed by an overwintering period near

the spring spawning site. This distinction also can be used to differentiate sympatric

subpopulations in many river systems (Bemis and Kynard 1997). Throughout the

southern portion of the range of the shortnose sturgeon, single-step migrations are

typical. Single-step migrations have been well documented in the Cape Fear (Moser

and Ross 1995), Cooper (Palmer 2001), Savannah (Hall et al. 1991, Collins and Smith

15

1993), and Altamaha (Heidt and Gilbert 1978, Flournoy et al. 1992, Rogers and Weber

1994) rivers. Among northern coastal rivers, two-step migrations have been

documented for shortnose sturgeon in the Hudson (Pekovitch 1979, Dovel et al. 1989),

Connecticut (Buckley and Kynard 1985), and Delaware (O’Herron et al. 1993) Rivers,

however, Kieffer and Kynard (1993) documented both migration types in the Merrimack

River. Regardless of which pattern is used, each of these studies has shown that

dispersal from the spawning site occurs immediately after spawning.

Distribution and Legal Status

Shortnose sturgeon inhabit large coastal rivers of the Atlantic coast of North America

from the St. John River in Canada to the St. John’s River in northeast Florida (Vladykov

and Greeley 1963, Moser and Ross 1995, Waldman et al. 2002, Collins et al. 2003). At

present, most stocks are depleted or extirpated over much of this range (Collins et al.

2002). Within the United States, shortnose sturgeon currently are protected under the

Endangered Species Act of 1973, having been listed by the U.S. Fish and Wildlife

Service as endangered in 1967. In 1980, Canada listed the shortnose sturgeon as a

species of special concern. The World Conservation Union (IUCN) has given the

shortnose sturgeon Red Book status as a vulnerable species throughout the range.

Mechanisms Leading to Declines

Overharvest

Sturgeon have long been harvested for both their flesh and roe, which is typically

processed for caviar. Klyszejko et al. (2004) found evidence that sturgeons were

16

commercially harvested in Europe dating back at least 1,000 years. Archeological

evidence from North America indicates that indigenous Americans also used sturgeons

as food for many centuries (Ritchie 1969). Beginning in the 1600’s, North American

sturgeon were commercially harvested for export to Europe (Murawski and Pacheco

1977). During the 1800’s, sturgeon were harvested not only for their roe and flesh, but

also used to make other products such as isinglass and paint additives (Scott and

Crossman 1973, Smith et al. 1984). In 1870, demand for sturgeon increased

dramatically and coastal stocks suffered serious declines. Landings fell from 2.9 million

kilograms 1892 in the Delaware Bay area to only 0.11 million by 1901 (Cobb 1900,

Gilbert 1989). After 1901, southern stocks became the major source of sturgeon in the

United States with harvest peaking in 1969 with 78,471 kg landed throughout the South

Atlantic Bight before declining once again (Murawski and Pacheco 1977, Smith et al.

1984, van den Avyle 1984, Gilbert 1989).

The importance of shortnose sturgeon to total landings prior to 1973 cannot be

evaluated because no distinction between shortnose sturgeon and Atlantic sturgeon

was made (Murawski and Pacheco 1977, Smith et al. 1984). LeSueur (1818)

commented that fishermen valued shortnose sturgeon more highly than the sympatric

Atlantic sturgeon because they had a higher market price. However, by 1890 the

shortnose sturgeon had virtually no economic importance because of its small size and

scarcity relative to the larger, more profitable Atlantic sturgeon (Ryder 1890). Today,

Atlantic sturgeon continue to be more sought after than shortnose sturgeon in Canadian

waters, where harvest continues on a limited basis (Trencia et al. 2002).

17

Since the shortnose sturgeon was listed as an endangered species in 1967, concern

over the frequency of incidental bycatch of shortnose sturgeon by commercial fisheries

has increased. Spawning migrations of shortnose sturgeon and American shad overlap

in time and space and commercial and recreational shad fishermen often catch the

migrating shortnose sturgeon in their nets (Dahlberg and Scott 1971, Scott and

Crossman 1973, Heidt and Gilbert 1978, Boreman et al. 1984, Collins et al. 1996,

Weber 1996, Collins and Smith 1997, Collins et al. 2000). Moser and Ross (1995) and

Weber (1996) reported that female shortnose sturgeon aborted eggs and returned

downstream when captured more than once. Collins et al. (1996) found that shrimp

trawlers, while routinely capturing juvenile Atlantic sturgeon, rarely encountered

shortnose sturgeon, however the commercial shad fishery had much higher encounter

rates (52 and 83% respectively) for both species.

Habitat Degradation

Shortnose sturgeon require specific habitats during various life stages and hence are

sensitive to habitat alterations. Construction of dams restricts movements and often

cuts off access to historic spawning grounds. Impoundments may also alter natural

river flow and temperature regimes needed for successful spawning (Kieffer and Kynard

1996, NMFS 1998, Cooke and Leach 2004). Though shortnose sturgeon apparently

are incapable of using modern fish ladders, fish lifts have been employed with limited

success in some rivers. For example, the fish lift located at Holyoke Dam on the

Connecticut River passed less than 5 shortnose sturgeon annually over a period of 21

years (Kynard 1998). With the loss of historic migratory routes, individuals downstream

18

of impoundments utilize spawning habitat similar to what had been historically utilized

and may spawn in close proximity to the impoundment (Kynard 1997, Cooke and Leach

2004, Duncan et al. 2004). Additionally, reproduction and recruitment within the

downstream segment of these impoundments is often poor, possibly prohibiting

recovery of these populations (Kynard 1997, Cooke and Leach 2004, Cooke et al.

2004).

Shortnose sturgeon also are thought to be sensitive to contaminants, which are

associated with impaired reproduction (Cameron et al. 1992, Longwell et al. 1992), early

survival (Dwyer et al. 2000) and susceptibility to disease (Sindermann 1979).

However, few studies have been conducted that examine these impacts. As long-lived,

benthic feeders, shortnose sturgeon are susceptible to bioaccumulation of heavy metals

and other contaminants (Dadswell 1979, Ruelle and Keenlyne 1993).

Other threats affecting recovery of shortnose sturgeon populations include dredging

and poor water quality. Dredging of navigation channels can destroy feeding habitats,

and there is documentation of mortalities from hydraulic pipeline operations (NMFS

1998). Industrial and agricultural discharge often contains contaminants that promote

high biological demand that results in lowered dissolved oxygen levels (NMFS 1998).

Low dissolved oxygen levels are of particular concern during early development of

shortnose sturgeon. Jenkins et al. (1993) found high mortality of juveniles less than 100

days old when dissolved oxygen concentrations were less than 2.5 mg/L. Although

shortnose sturgeon tolerance of low dissolved oxygen appears to increase with age,

Flournoy et al. (1992) reported that adults were stressed during periods of high

temperature and low dissolved oxygen levels. Over these periods, sturgeon often

19

congregate in deeper, cooler river regions that help alleviate the physiological stress

associated with high temperatures (Flournoy et al. 1992, Mason and Clugston 1993).

Absence of habitat that provide such refugia, especially in southern populations, has

been attributed to high juvenile mortality and extirpation of some populations (Collins

and Smith 1993, Rogers et al. 1994, Rogers and Weber 1995, Collins et al. 2000).

Management Approaches

Stocking and Reintroductions

Over the past two decades, increasing interest in shortnose sturgeon restoration has

spurred debate over whether supplemental stocking is an effective method for

recovering populations. From 1984-1992, the South Carolina Department of Natural

Resources supplemented the Savannah River shortnose population with nearly 100,000

mostly juvenile individuals in response to low juvenile recruitment (Smith and Collins

1996, Smith et al. 2002). Subsequent captures of released hatchery-reared shortnose

sturgeon in neighboring rivers revealed that many individuals did not remain within the

Savannah River system. Those stocked individuals may now constitute a portion of the

total population within those rivers in addition to the Savannah (Smith et al. 2002).

Despite the augmentation of the Savannah River population of shortnose sturgeon, no

increase in juvenile recruitment has been documented in either the Savannah or the

adjacent Ogeechee River suggesting a recruitment bottleneck as juveniles mature

(Collins et al. 2002a, Fleming et al. 2003). Based on the results of this stocking event,

the National Marine Fisheries Service (NMFS) developed guidelines to determine if

augmentation was feasible. Their effort focused on the population status, habitat quality

20

and availability, and availability of natal population broodstock (NMFS 1998). However,

these guidelines have not yet been applied because many rivers with populations in

imminent danger of extirpation continue to have significant anthropogenic factors

prohibiting natural recovery (NMFS 1998). Because of the susceptibility of small

populations to anthropogenic factors, there have been no approved stocking events

since the Savannah River was augmented.

Habitat Protection and Restoration

Habitat loss and degradation threaten the continued survival of shortnose sturgeon

in many rivers. To date, restoration efforts that failed to address the issue of habitat

degradation have generally been unsuccessful (Beamesderfer and Farr 1997). These

efforts have included supplemental stocking and habitat restoration. Because

shortnose sturgeon are more susceptible than many other fish species to

overexploitation because of their longevity, delayed maturation, and spawning

periodicity (Beamesderfer and Farr 1997), they may serve as indicators for system

degradation.

Research Objectives and Justification

Information about the shortnose sturgeon population in the Altamaha River system is

meager. Heidt and Gilbert (1978), Flournoy et al. (1992) and Rogers and Weber (1994)

provide some qualitative information about the status of the Altamaha River population

prior to implementation of the National Marine Fisheries Service (NMFS) recovery plan.

Because there are no current data, the effectiveness of the recovery plan for increasing

21

recruitment and protecting adults has not been evaluated. Additional quantitative data

on population size and structure are needed to allow regulatory agencies, such as

NMFS, to evaluate the effectiveness of the current recovery plan for the Altamaha

shortnose sturgeon population. To date, implementation of this plan has been limited.

Areas of interest have focused primarily on field research (mark-recapture, telemetry,

essential habitat quantification, bycatch assessment, stock augmentation assessment,

etc.). More recent studies have examined the genetic relationships among rivers.

However, because not all populations are currently being investigated, information on

many smaller populations may be outdated or absent.

Protection of spawning habitat is also a crucial component of the NMFS plan for

recovering shortnose sturgeons. Although spawning habitats of shortnose sturgeon

have not been identified in the Altamaha River, previous studies have shown that

spawning shortnose sturgeon select habitats with suitable flow and substrate

characteristics. For spawning to occur, current velocity of 37-125 cm/s is needed

(Pekovitch 1979, Taubert and Dadswell 1980, Buckley and Kynard 1985). Slower flow

allows eggs to clump together while higher velocity currents may prevent the eggs from

adhering to the substrate (Dadswell 1979, Buckley and Kynard 1985, Kynard 1997).

Substrates typically used by spawning shortnose sturgeon consist of sand, gravel,

cobble, or rubble bottoms (Dadswell et al. 1984, Gilbert 1989, Hall 1991, Kynard 1997)

Given the general lack of knowledge regarding the current status of Altamaha River

shortnose sturgeon, this study had three primary objectives: 1) to estimate the number

of shortnose sturgeon, 2) to evaluate the current population age structure, and, 3)

identify spawning sites of shortnose sturgeon in the Altamaha River. This population

22

assessment will help quantify what is thought to be a critically endangered population of

shortnose sturgeon while providing insight into possible trends in abundance.

Identification of spawning habitat will allow local management agencies to protect these

areas in the Altamaha as specified in the NMFS recovery plan.

23

CHAPTER 2

STUDY AREA AND METHODS

Study Site Description

Located entirely within Georgia, the Altamaha River and its main tributaries, the

Oconee and Ocmulgee Rivers, flow over 800 km from the headwaters near Atlanta,

Georgia to the Atlantic Ocean near Darien and drains nearly one-third of the state

(Figure 2.1). Encompassing approximately 36,000 km2, this river system is one of the

largest watersheds on the east coast of the United States and was recently listed as the

seventh most endangered river in the United States by the advocacy group American

Rivers. The Altamaha River is also second only to the Pascagoula River in Mississippi

in length of unimpounded stretch of river from the ocean east of the Mississippi River.

Dynesius and Nilsson (1994) attributed the more than 600 km of unimpounded river to a

lower rate of exploitation by a smaller regional population. The Altamaha is formed at

the convergence of the Ocmulgee and Oconee Rivers 215 river kilometers (rkm) inland.

It averages 50-70 m in width and 2-3 m in depth with a maximum depth of 18 m (Heidt

and Gilbert 1978). The Oconee and Ocmulgee Rivers contain the only impoundments

within the watershed; however, none are found farther downstream than 361 rkm, which

is well upstream of the known habitat of shortnose sturgeon in this system (Rogers and

Weber 1994). Vegetation along the lower reaches of the watershed progresses from

mixed hardwood to cypress swamp to salt marsh (Spartina spp.) near the estuary.

Lloyd Shoals Dam

rkm 604 Sinclair Dam rkm 444

Juliette Dam rkm 573 Oconee

River

Ocmulgee River

Altamaha River

Figure 2.1 The Altamaha River watershed (gray) including the headwater tributaries,

the Ocmulgee and Oconee Rivers with impoundments.

25

26

The average gradient over the lower 200 rkm is 0.13 m per km (GEPD 2003). Average

annual discharge is 381 m3s-1, or 18% of the entire freshwater input to the South

Atlantic shelf (Rogers and Weber 1994).

The sampling area of this study included the entire tidally influenced portion of the

lower river from Altamaha Sound upstream to rkm 40 when (Fig 2.2). I chose net

sampling locations based on the amount of woody debris on the river bottom. Input

from individuals with prior experience in capturing sturgeon also was an important factor

in site selection. To identify potential sampling sites, I first surveyed the river bottom

with a Furuno LS-6100 depth finder prior to gear deployment to ensure that the river

bottom was clear of debris or structure that might otherwise damage sampling gear.

Sites where sampling was not possible either through loss of gear or having extensive

bottom structure were eliminated from sampling. Water quality variables such as

dissolved oxygen, temperature, conductivity, and salinity were measured with a YSI-85

® meter.

Materials and Methods

I sampled the Altamaha River tidal zone from 14 November 2003 to 18 December

2005. I captured shortnose sturgeon were captured with 94.4 m long, 3 m deep

monofilament gill nets and trammel nets hung in a 2:1 ratio. Gill nets were constructed

from single 10.2 cm or 15.2 cm stretched mesh panels and experimental gill nets from

3-30.5m panels of 7.6, 10.2, and 15.2 cm stretched mesh hung in varying orders of

arrangement. Trammel nets were constructed from a single inner panel of 7.6 cm

stretched mesh surrounded by 2-30.5 cm stretched mesh panels. Nets were deployed

Figure 2.2 Shortnose sturgeon capture sites in the tidally influenced lower 40 rkm of the Altamaha River (sampling sites

27

Study Area

are denoted by o).

only during slack tides—typically 45-90 minutes—due to the large tidal amplitudes and

resulting currents. Nets were deployed perpendicular to the current, with net ends

anchored on the river bottom by a 6.8 kg navy anchor attached to the net end by a 0.9

m bridle. Soak time was reduced to 25-30 minutes during summer months when

temperatures exceeded 27 oC to minimize stress and reduce the chance of heat-related

mortalities of shortnose sturgeon (Moser et al. 2000). During net retrieval, all shortnose

sturgeon captured were placed in floating net pens until processing. Each fish was

measured—total length (TL) and fork length (FL) to the nearest mm, weighed to the

nearest 2 g (20 g for individuals heavier than 1.2 kg), and checked for tags. If a tag was

not present, fish were injected with a passive integrated transponder (PIT) tag under the

forth dorsal scute (125 kHz, Biomark). One centimeter segments also were removed

from the leading left pectoral fin ray of a subsample of shortnose sturgeon to estimate

age.

Abundance Estimates

I estimated population size using POPAN-5 within Program MARK (White and

Burnham, Colorado State University). The POPAN-5 program used to estimate

population size in this study is a robust parameterization of the Jolly-Seber model.

Model selection in POPAN is determined by Akaike’s Information Criteria (AIC).

Maximum Likelihood Estimation (MLE) addressed heterogeneity within the models

(Williams et al. 2002). Assumptions with the models vary with the parameterization;

however, the assumptions used in my study were 1) the population was closed to gains

and losses during the each sampling period, 2) tags were not lost or overlooked and are

28

correctly recorded, 3) all fish had equal capture probabilities during all sampling periods,

and 4) survival of each individual was independent of capture probability.

To compare this model with previous estimates for the Altamaha River shortnose

sturgeon population, I conducted a Schnabel estimate for the summers of 2004 and

2005. The assumptions of the Schnabel estimator were: 1) the population was closed

to gains and losses during the sampling periods, 2) marked and unmarked fish were

equally vulnerable to sampling gear, 3) marked fish mix randomly with unmarked fish,

and 4) tags were not lost and marks were not overlooked.

Data used both for the POPAN and the Schnabel estimates were for June-August of

2004 and 2005 only. This was because capture and recapture rates for the remainder

of the year was very low comparatively and because Program MARK can not account

for continuous sampling.

Population Age Structure

Age Determination

I evaluated population age structure using cross sections of pectoral fin spine

samples collected from a stratified subsample of 68 shortnose sturgeon. Age of each

shortnose sturgeon in the subsample was determined from a 1-2 cm segment of the left

leading pectoral fin ray which was removed using a small coping saw (Fleming et al.

2003). This procedure was performed only during cooler months when water

temperature was below 27 oC to minimize the risk of mortality associated with additional

handling. Once removed from the fish, each segment was either allowed to air dry for

45 days or dried in an oven at 65.5o C for 4 hours. Once dry, a Buehler low-speed saw

29

was used to cut the segments to a thickness of 0.50-0.75 mm. Each cross section of

each fin ray segment was mounted on an individual glass slide and viewed by two

independent readers without prior knowledge of fish size, date, or capture location at

30x magnification on a Leica MZ6 dissecting microscope. All disagreements in

assigned ages were reconciled by mutual agreement between observers.

I evaluated the precision of age estimates by coefficient of variation (CV) as given in

the equation:

CV = 100 x XjR

XjXijR

i∑= −

−

1

2

1)(

where R is the number of reads per sample, Xij is the i th determination of the j th fish,

and Xj is the mean age of the j th fish (Chang 1982). This formula gives a single value

for each sample and reader which were averaged across of all spines to give a mean

estimate of precision. The index values were used to evaluate whether error increased

with older fish and to compare the error rate with reported values from other studies on

long-lived fish. Differences in age estimates among readers were plotted and compared

to a line where the slope is equal to 1 (complete agreement) to detect reader bias

(Campana et al. 1995).

An age-frequency histogram was constructed to illustrate the age structure of the

population. Annual mortality was calculated from the catch curve constructed from

these data by linear regression.

I also used the von Bertalanffy growth equation to estimate both the growth

coefficient and the maximum size potential of shortnose sturgeon in the Altamaha River.

The von Bertalanffy growth model is described by the equation:

30

⎥⎥⎦

⎤

⎢⎢⎣

⎡ −−−∞=

⎟⎟⎠

⎞⎜⎜⎝

⎛

0ttKexp1TLtTL

where TLt is the mean predicted length (mm) at age t, TL∞ is the average asymptotic

length of shortnose sturgeon, t0 is the x-intercept associated with the predicted age at

which size is 0 mm, and K is the Brody growth coefficient (Ricker 1975). Parameters

were estimated using the program FiSAT II © (FAO-ICLARM Fish Stock Assessment

Tools 2000), which uses regression to estimate the parameters TL∞, t0, and K.

Predicted weight-at-age from the von Bertalanffy growth model was obtained using the

equation:

Wt = a(TL)b

where the growth parameter b was fitted by regression. The von Bertalanffy growth

model for weight is:

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡ −−−∞=

⎟⎟⎠

⎞⎜⎜⎝

⎛ b0ttK

exp1WtWt

where Wt is the mean predicted weight (g) at age t, W∞ is the average asymptotic

weight (g) of shortnose sturgeon, and t0 and K are parameteritized as per the length-at

age model above. I used this equation to evaluate the growth rates of shortnose

sturgeon in the Altamaha River over time.

Gear Selectivity

Because age data can be biased by gear selectivity, I also evaluated the effect that

the sampling gear may have had on the size of shortnose sturgeon captured. I

estimated mesh selectivity values through manipulation of the equation:

Cm,l = ql,m Nl Pm Sm,l

31

where Cm,l is catch by mesh size m for a given length class l; ql,m is catchability of

length class l in mesh size m; Nl is the abundance of fish of length class l; Pm is the

fishing power or efficiency of mesh size m; and Sm,l is the selection of mesh size m for

length class l (Hovgård and Lassen 2000).

For gear selectivity bias analysis, I used the Baranov model, which assumes that

each mesh size will be the most efficient at capturing a fish of length, lo. I also used the

NORMSEP process within the program FiSAT II © (FAO-ICLARM Fish Stock

Assessment Tools 2000) to generate selectivity curves under the assumptions of the

Baranov model. This procedure uses maximum likelihood estimates to divide length-

frequency classes for each mesh size into normally distributed selectivity curves. All

curves were scaled to a maximum value of 1 (Hamley 1975).

Data Analysis

I evaluated gear selectivity separately for 2004 and 2005. Based on the results from

2004, evaluating gear selectivity became a secondary objective to this study. In 2004, I

compared lengths of shortnose sturgeon captured in trammel nets with those captured

in 10.2 cm and 15.2 cm gill nets. In 2005 I substituted the 10.2 cm and 15.2 cm gill nets

for two experimental nets of 7.6, 10.2, and 15.2 cm stretched mesh hung in different

arrangements and compared lengths of shortnose sturgeon to those captured in

trammel nets only in 2005. To compare sampling efficiency among net types in the

2004, I used a two-way ANOVA with a factorial arrangement of treatments to compare

the effects on catch per unit of effort (CPUE) of net type, tidal stage, and possible

interaction of these variables. CPUE was calculated by determining the number of

32

sturgeon caught per net set. To evaluate potential size selectivity of different net types,

I used Tukey’s honestly significant difference (hsd), which is a conservative means

comparison test, to compare the mean size captured for each net type. Juveniles were

considered to be all fish less than 600 mm TL. This number was derived using linear

regression stipulating the size at maturity as reported by Rogers and Weber (1994). In

2005, I used a two-way ANOVA with a factorial arrangement of treatments to compare

the effects of net types, tides, and possible interactions on CPUE of each net type and

tidal stage for both shortnose sturgeon and other non-target species. To contrast size

selectivity of the net types in 2005, I used t-tests to compare the mean sizes of

shortnose sturgeon captured for each net type for juvenile and adult shortnose

sturgeon. Juveniles and adults were analyzed separately to evaluate susceptibility of

both life stages to the sampling gear. All statistical tests were conducted with an alpha

of 0.05.

Identification of Critical Habitat

To identify potentially critical habitat locations of shortnose sturgeon, I used radio

telemetry to monitor seasonal movements of 12 adult shortnose sturgeon. The radio

tags, manufactured by Advanced Telemetry Systems (Isanti, Minnesota) measured 68

mm in length, 32 mm in width, and weighed 25 g in air. Each tag was programmed to

operate on a 12-hour duty cycle at 48-49 MHz. The battery life of the tags was

approximately 5 years. Tags were surgically implanted into adult shortnose sturgeon

after each tag was coated with an inert elastomer to reduce rejection potential. Adult

shortnose sturgeon selected for radio tracking weighed a minimum of 1,250 g to ensure

33

that weight was <2% of the fish’s body weight as recommended by Winter (1983). I

performed surgeries on shortnose sturgeon in the fall and early winter after water

temperature had fallen to 10.9 o - 21.4 oC, to minimize handling stress (Moser and Ross

1995, Moser et al. 2000). Individuals implanted with tags were first anesthetized in a

250 mg/L solution of tricaine methanesulfonate (MS-222). The fish were then placed on

a portable surgical table equipped with a recirculating pump that maintained a constant

flow of anesthetic (85 mg/L MS-222 and 170 mg/L NaHCO3 buffer in 60 L of water) over

the gills during the procedure. Sex and reproductive condition was determined using a

Karl Storz model 26006 AA laparoscope to examine the gonads of each fish as

described by Hernandez-Divers et al. (2004). Only those fish observed to be in

spawning condition were selected for insertion of radio tags.

This surgical procedure was performed by first making an incision about 4.5 cm long

to allow for insertion of a transmitter. A cordless drill was used to drill a 2 mm hole into

a ventral-lateral scute (located slightly posterior to the incision). A metal catheter was

then inserted through this hole until it reached through the body wall and into the body

cavity. The antennae was inserted through the catheter, the catheter removed, and the

rest of the tag inserted into the abdomen. The incision was closed with a 3/0 cutting

needle attached to a non-absorbable braided nylon suture. The entire procedure

typically required less than 3 minutes. Prior to release, each fish was allowed to

recover by holding the fish in non-treated river water and slowly moving the fish around.

The fish was released once it had regained its balance and could swim without

assistance.

34

35

Tracking of radio-tagged fish was conducted on a weekly basis from a small boat

equipped with a scanning receiver and loop antenna. The area surveyed extended from

10 rkm above the confluence of both the Oconee and Ocmulgee rivers to the coast

(Figure 2.3). Locations of radio-tagged fish were marked to the nearest meter possible

using a handheld GPS receiver. GIS mapping of these data was used to identify

potential spawning sites based on 1) the relative number of fish using an area and 2),

the relative duration of each fish’s stay. I also used a ponar grab to determine bottom

composition where each fish was located.

To confirm spawning at suspected spawning sites, I deployed artificial egg-sampling

mats during February and March 2005. The egg mats were constructed from 40 cm x

20 cm x 10 cm cinder blocks wrapped with hog-hair filter material. Pairs of egg mats

were placed 1 m apart and marked by a single buoy. The number of egg mats

deployed at each site ranged from 5-15 and varied with current velocity and bottom

composition. The egg mats were retrieved and visually examined every three days.

Recovered eggs were preserved in 70% ethanol.

Figure 2.3. Altamaha River basin covered on a weekly basis by boat equipped with a scanning receiver and loop

Head of tide rkm 40

Doctortown rkm ~97

Confluence

36

rkm 215

Baxley rkm 180

Study Area

antennae.

CHAPTER 3

RESULTS

Abundance Estimates

In late 2003 and throughout 2004, I set a total of 612 nets and captured 644

shortnose sturgeon, 49 of which were later recaptured. In 2005, effort was reduced to

276 net sets, yet 283 shortnose sturgeon were captured with an additional 40

recaptured. In total, 929 nets were deployed and 927 captured shortnose sturgeon and

89 subsequently recaptured. Sizes of captured shortnose sturgeon ranged from 290 to

1166 mm TL (Figure 3.1). CPUE averaged 1.16 fish per net set (274.2 m of

entanglement gear fished for 1 slack tide), but varied with season and gear type (Table

3.1). CPUE during July 2004 was greater than at any other time during the study, with a

range of 1.0—23.9 fish/net set (Figure 3.2).

Population estimates ranged between 3400-8233 with the Schnabel method and was

6320 (95% C.I. 4387-9249) using POPAN (Table 3.2). The POPAN estimate assumed

that apparent survival and recapture probability varied temporally and entry probability

was constant. Initial population size did not affect the model through either temporal

variation or constancy.

2004

0.00

0.05

0.10

0.15

0.20

0.25

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

CPU

E

2005

0.00

0.05

0.10

0.15

0.20

0.25

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

TL (mm)

CPU

E

n = 323

Figure 3.1. Size distributions of captured shortnose sturgeon from the Altamaha River, Georgia in 2004 (top)

and 2005 (bottom). In 2004, individuals were caught in 10.2 and 15.2 cm gill nets and trammel nets. In 2005,

n = 685

gill nets were replaced with experimental gill nets constructed from 7.6, 10.2, and 15.2 cm panels.

38

Year Net No. Net Sets

No. Shortnose Captured CPUE Relative

Efficiency

2004 Trammel Net 144 252 1.75 100.0

2004 10.2 cm Gill Net 144 52 0.36 20.6

2004 15.2 cm Gill Net 144 104 0.72 41.3

2005 Trammel Net 48 112 2.33 100.0

2005 Experimental Gill Net 96 136 1.42 60.7

39

Table 3.1. Trammel net and gill net capture comparison in 2004 and 2005. Trammel

nets were constructed from an inner panel of 7.6 cm and 2 outer panels of 30.5 cm

stretched mesh. Gill nets were constructed from 10.2 and 15.2 cm stretched mesh.

Experimental gill nets were constructed from 7.6, 10.2, and 15.2 cm stretched mesh.

CPUE is defined in terms of number of shortnose sturgeon captured per net set.

Figure 3.2. Monthly catch per unit effort (CPUE) of shortnose sturgeon in the Altamaha River for 2004 and 2005.

(Sampling not conducted during months denoted with an asterisk.)

2004

0.000

2.000

4.000

6.000

Jan Feb Mar Apr May June July Aug Sept Oct Nov DecMonth

CPU

E

2005

0.000

2.000

4.000

6.000

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

Month

CPU

E

* *

40

Table 3.2. Estimates of shortnose sturgeon abundance in the Altamaha River, Georgia.

Population Estimator (Model)

Model Type

N 95%

Confidence Interval

Sample Period

Schnabel closed 8233 5083 – 21656 1 June 2004 – 31 August 2004

Schnabel closed 3400 2008 – 11074 1 June 2005 – 31 August 2005

POPAN open 6320 4387 – 9249 1 June 2004 – 31 August 2004,

1 June 2005 – 31 August 2005

^

41

Population Age Structure

Age and Growth

Nominal ages determined for 68 fish ranged between 1 - 14, with a modal age of 4

and a mean age of 5.9 (Figure 3.3). Interpretation of annuli was difficult and agreement

among observers was only 55%. However, disagreements of one year (37%)

constituted the majority of the remaining fin ray samples. The greatest age discrepancy

encountered was 2 years, which occurred in 5 individuals. Precision among observers

was variable with a coefficient of variance of 4.58 across both observers and all age

groups. A visual assessment of age-bias plots between observers (Figure 3.4)

indicated that age estimates were relatively precise and that error rates did not increase

with older fish.

Using the von Bertalanffy growth equation, I developed a single growth curve (Figure

3.5) for the Altamaha River population of shortnose sturgeon. The weight to length

relation was

Wt = 775( )

⎥⎦⎤

⎢⎣⎡ −−−

3.401.58t0.09exp1

(Figure 3.6).

Total annual mortality based on uncorrected catch curves (Figures 3.7 and 3.8) was

estimated to be 29% and 37%, respectively. This rate was estimated for fish between

ages 4-12 only because fish from older age classes were rarely captured and because

of the presence of a large cohort of juvenile fish (Tables 3.3 and 3.4). In 2005, this

cohort began to affect the slope of the catch curve, indicating a higher mortality rate

than expected. When the mortality rate was recalculated without this cohort, the

42

43

estimate fell to 34%. Maximum average life span, based on the uncorrected catch

curves was estimated to be 14-15 years.

Gear Selectivity

Each net type and mesh size had a unique lo that corresponded with mesh size

(Figures 3.9 and 3.10). The trammel net, with a 7.6 cm inner panel, had a lower lo in

both sampling periods and lo increased with mesh size. Experimental gill nets and

trammel nets had similar lo’s and selectivity curves. Trammel net lo’s increased from

2004 to 2005 as growth occurred over time.

Trammel nets caught a wider size range of shortnose sturgeon (Figure 3.11) than

either the 10.2 cm or 15.2 cm gill nets in 2004. The results of the ANOVA show that

trammel nets catch a significantly smaller mean size for both juvenile and adult

shortnose sturgeon than did either the 10.2 cm or 15.2 cm gillnets (juveniles:

F2,178=16.00, p<0.0001; adults: F2,166=6.87, p=0.0014). The 10.2 cm or 15.2 cm gill nets

were also found to capture significantly different sizes of both juvenile and adult

shortnose sturgeon (juveniles: mean difference=118.72, 95% confidence limit=15.65-

221.787; adults: mean difference=75.77, 95% confidence limit=20.11-131.42).

Trammel nets caught significantly smaller individuals of juvenile shortnose sturgeon

(Figure 3.12) than did the experimental gill nets (t191=2.59, p=0.0102) in 2005. Trammel

nets and experimental gill nets caught similar size ranges of shortnose sturgeon

individuals, but experimental gill nets caught a higher number of individuals larger than

600 mm TL.

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Age (years)

Freq

uenc

y

Figure 3.3. Nominal age frequency of shortnose sturgeon captured in the Altamaha River, Georgia in 2005. Ages of

individual fish were determined from pectoral fin ray sections and interpreted by 3 independent observers.

44

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14 16

First interpreter estimates

Seco

nd in

terp

rete

r est

imat

es

CV = 4.58%

Figure 3.4. Age-bias graph for 2 interpreters of sampled fin rays from Altamaha River shortnose sturgeon. The

dashed line designates the 1:1 ratio line.

45

0

200

400

600

800

1000

1200

0 4 8 12 16 20

Age

Tota

l Len

gth

(mm

)

AltamahaHudsonOgeechee

TL = 1389 (1-exp -0.09 ( t-1.58 ))

Figure 3.5. Growth of shortnose sturgeon (both sexes) in the Altamaha River, Ogeechee River, and Hudson River.

46

0

2000

4000

6000

8000

10000

12000

0 200 400 600 800 1000 1200 1400

TL (mm)

Wei

ght (

g)

R2 = 0.9847n = 1012

Figure 3.6. Weight – length relationship of shortnose sturgeon (both sexes) from the Altamaha River, Georgia.

47

Table 3.3. Age-frequency key for shortnose sturgeon captured in the Altamaha River system in 2004. Ages were

determined from the first pectoral fin ray. Final ages from each individual subsample were applied proportionally across

the same length-group. Note: age-2 or age-13 individuals were not obtained during this study.

Age 1 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8 Age 9 Age 10 Age 11 Age 12 Age 14

≤ 300 1 1(1) 1301 - 400 277 5(1) 277401 - 500 39 2(3), 8(4) 8 31501 - 600 29 8(4), 8(5), 3(6) 12 12 5601 - 700 37 2(5), 3(6), 4(7) 8 12 16701 - 800 21 3(6), 2(7), 1(8) 11 7 4

801 - 900 24 4(7), 2(9), 2(11) 12 6 6

901 - 1000 14 1(7), 2(8), 1(9), 1(10), 1(12) 2 5 2 2 2

1001 - 1100 2 1(8), 1(10), 1(12), 1(14) 1 1 1 1

1101 - 1200 2> 1200

Total 446 278 8 43 20 28 37 10 8 3 6 3 1

Length group (mm)

Number in

sample

Number (age) in subsample

Sample allocation per age - group

48

Table 3.4. Age-frequency key for shortnose sturgeon captured in the Altamaha River system in 2005. Ages were

determined from the first pectoral fin ray. Final ages from each individual subsample were applied proportionally across

the same length-group. Note: age-2 or age-13 individuals were not obtained during this study.

Age 1 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8 Age 9 Age 10 Age 11 Age 12 Age 14

≤ 300 1(1) 4301 - 400 4 5(1) 23 92401 - 500 115 2(3), 8(4) 43 43 16501 - 600 103 8(4), 8(5), 3(6) 5 7 10601 - 700 22 2(5), 3(6), 4(7) 7 4 2701 - 800 13 3(6), 2(7), 1(8) 10 5 5

801 - 900 20 4(7), 2(9), 2(11) 1 3 1 1 1

901 - 1000 8 1(7), 2(8), 1(9), 1(10), 1(12) 2 2 2 2

1001 - 1100 6 1(8), 1(10), 1(12), 1(14)

1101 - 1200> 1200

Total 291 4 23 135 48 30 25 6 6 3 5 3 2

Length group (mm)

Number in

sample

Number (age) in subsample

Sample allocation per age - group

49

y = -0.3441x + 5.1842R2 = 0.8076

n = 158

0.0

1.0

2.0

3.0

4.0

5.0

6.0

3 4 5 6 7 8 9 10 11 12 13

Age

Ln N

umbe

r Cau

ght

M = 0.291Maximum Age = 15

Figure 3.7. 2004 uncorrected catch curve for ages 4 – 12 of Altamaha River shortnose sturgeon.

50

y = -0.4731x + 6.3189R2 = 0.8984

n = 291

0.0

1.0

2.0

3.0

4.0

5.0

6.0

3 4 5 6 7 8 9 10 11 12 13

Age

Ln N

umbe

r Cau

ght

M = 0.377Maximum Age = 13

Figure 3.8. 2005 uncorrected catch curve for ages 4 – 12 of Altamaha River shortnose sturgeon.

51

Trammel nets

0.00

0.20

0.40

0.60

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

CPU

E

Gill nets

0.00

0.20

0.40

0.60

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

TL (mm)

CPU

E

10.2 cm15.2 cm

Figure 3.9. Size composition of shortnose sturgeon captured in trammel nets and gill nets from the Altamaha River,

Georgia in 2004. Catch per unit effort is the number of shortnose sturgeon captured per net per slack tide.

52

Trammel nets

0.00

0.20

0.40

0.60

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

CPU

E

Experimental gill nets

0.00

0.20

0.40

0.60

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

TL (mm)

CPU

E

Figure 3.10. Size composition of shortnose sturgeon captured in trammel nets and experimental gill nets (constructed

from 7.6, 10.2, and 15.2 cm stretched mesh) from the Altamaha River, Georgia in 2004. Catch per unit effort is the

number of shortnose sturgeon captured per net per slack tide.

53

lo = 501

lo = 673 lo = 835

0

0.2

0.4

0.6

0.8

1

200 300 400 500 600 700 800 900 1000 1100

TL (mm)

Sele

ctiv

ity

Trammel net ( ) n = 252 10.2 cm gill net ( o ) n = 52 15.2 cm gill net ( ) n = 104

Figure 3.11. Indirect selectivity of trammel nets, 10.2 cm, and 15.2 cm stretched mesh gill nets from the Altamaha

River, Georgia in 2004.

54

Figure 3.12. Indirect selectivity of trammel nets, and experimental gill nets composed of 7.6, 10.2, and 15.2 stretched

55

0

0.2

0.4

0.6

0.8

1

200 300 400 500 600 700 800 900 1000 1100

TL (mm)

Sele

ctiv

itylo = 537 lo = 597

Trammel net ( ) n = 112 Experimental gill net ( o ) n = 136

mesh panels from the Altamaha River, Georgia in 2005.

Habitat and Seasonal Movements

When water temperatures exceeded 27 oC, all radio tagged shortnose sturgeon were

located above the salt-fresh water interface. In 2004, the interface was located as far

inland as rkm 22. River bottom temperatures exceeded 31 oC and dissolved oxygen

(DO) levels fell as low 4.53 mg/L throughout the tidally influenced portion of the river.

Most captures (as many as 23.9 fish per net set) during this time period were in a single

river segment at rkm 22.5 referred to as Ebenezer Bend. This stretch of river reaches a

depth of 16 m at mean low tide and has large woody debris along much of the mostly

sandy bottom.

From mid-August to September of 2004, multiple tropical storm systems moved

through the area and caused discharge to increase and temperatures to decrease.

When sampling resumed in mid-October, water temperature had fallen to 20.2 oC, DO

increased to 5.82 mg/L and capture rates were lower above rkm 20 while increasing

throughout the estuary. During winter, when water temperatures fell below 14 oC,

adults were captured in Altamaha Sound in salinities greater than 18 ‰.

Eight male and 4 female (≥ 768 mm TL) shortnose sturgeon were radio-tagged

between 14 November 2004 and 14 January 2005 (Table 3.5). Nine of these were

tracked until the end of 2005. The remaining individuals were censored after movement

was not detected, or they were not relocated, after a period of 4 months. Periodic

checks for an additional 2 months also showed no movement. There were no known

mortalities directly attributable to the implantation procedure; however, the status of

individuals that were not relocated is unknown.

56

Upstream movement of radio tagged fish, possibly associated with spawning runs,

commenced in mid-December when water temperature was 10.2o C. I observed

ripening females as early as mid-November. Of the 4 females I radio-tagged, at least 3

of these made upstream migrations. The first radio tagged female left the estuary 4

December 2004 and was located near Doctortown (rkm 89). Additional movement was

only 7 rkm upstream 5 days after it was initially located. Further movement was not

observed. Two other females completed runs into the Ocmulgee and Oconee rivers

(individually) and remained there for a period of one week prior to moving downstream

at a rate of 40 km/day. One of these females traveled a distance of at least 340 rkm

over 6 weeks and moved at a rate of nearly 5 km per hour (as determined by monitoring

for a period of 1.5 hours) during downstream migration.

When tracking both of these females, contact was lost at the confluence of the

Ocmulgee and Oconee rivers. This area is characterized by a sandy substrate with a

deep hole excavated by the fast, converging currents. Eggs mats were deployed

throughout this area and 2 eggs were recovered on 20 March, 2005, when the water

temperature was 12 oC. I located two other individual shortnose sturgeon between rkm

159.6 – 178.4 prior to them returning downstream. A single male moved upstream to

rkm 133.2 in late spring of 2006, but returned downstream to rkm 92-94, where it had

resided for the previous year. Based upon these individuals, I was able to identify 1

confirmed and 2 suspected spawning sites (Figure 3.13)

Non-spawning habitat was located in 2 discrete areas: the tidally influenced portion

of the lower river (rkm <40) and slightly below Doctortown (rkm 90-95) (Figure 3.14).

This area was categorized as non-spawning habitat because individuals were present

57

throughout the year and attempts to recover eggs at this location were unsuccessful.

This upstream habitat is much deeper (7.6 m) relative to the surrounding stretches of

river (~3 m depth) and Ponar grabs revealed that the substrate is composed of sand

with large numbers of small bivalves and aquatic insects. Movements greater than 2

rkm were not observed in either summering area while river temperatures exceeded

27 oC.

58

59

49.771 mal

49.781 mal

49.791 mal

49.801 mal

49.811 femal

49.831 femal

49.841 femal

49.871 femal

49.881 mal

49.891 mal

49.901 mal

49.921 mal

Days at Lar

Table 3.5. Radio tagged shortnose sturgeon release dates and number of relocations in

the Altamaha River, Georgia. The * denotes an individual tag that did not change

locations after an initial ~100 km upstream migration after tag implantation. ** indicates

a censored individual after x days at large.

geNo.

RelocationsRadio

Frequency Sex Date Released

e 11 Nov. 2004 15 340

e 22 Jan. 2005 0 unknown **

e 16 Dec. 2004 17 328

e 18 Nov. 2004 25 265

e 22 Jan. 2005 1 125 **

e 10 Dec. 2004 22 352

e 22 Jan. 2005 25 326

e 12 Nov. 2004 29 * 327 **

e 14 Jan. 2005 19 277

e 14 Jan. 2005 16 270

e 17 Dec. 2004 14 364

e 6 Jan. 2005 15 345

Suspected spawning area

rkm 160 -170 I-95

Confirmed spawning site (rkm 215)

rkm 110-120

U.S. 1

Figure 3.13. Confirmed and suspected spawning areas of shortnose sturgeon in the Altamaha River, GA (2005).

60

Figure 3.14. Non-spawning habitat of shortnose sturgeon in the Altamaha River, GA (April-December 2005).

61

3 fish 42 relocations (rkm 95-100)

8 fish

I-95

Head of tide

73 relocationsU.S. 1

CHAPTER 4

DISCUSSION

Abundance Estimates

Since shortnose sturgeon were initially listed as endangered in 1967, most

populations have remained depressed (Moser and Ross 1995); however, the

abundance estimate of 6320 (95% C.I. 4387-9249) obtained in this study is nearly ten

times larger than the previous estimate of 650 reported by Kynard (1997—from Rogers

and Weber, unpublished data). My results show that the Altamaha River population of

shortnose sturgeon is probably the fourth largest in the United States, and the largest

south of Chesapeake Bay (Squiers et al. 1982, Hastings et al. 1987, Bain et al. 1995,

NMFS 1998). Although continued study is needed to determine if the population is

remaining stable in the face of ongoing environmental challenges within the Altamaha

watershed, the results of this study suggest that the Altamaha River supports one of the

largest known populations of shortnose sturgeon. Furthermore, small populations in

adjacent rivers may be sustained by immigrating Altamaha individuals in lieu of poor

reproduction by resident individuals (Wirgin et al. 2005). Northern rivers with large

populations (e.g., the Hudson and Delaware rivers) may also supplement adjacent

smaller populations through immigrants and transients (Welsh 2002); however, the

actual genetic contribution to these smaller populations is uncertain. Wirgin et al.

(2005) reported that haplotypes of shortnose sturgeon from the Altamaha and

62

Ogeechee river populations were not significantly different, which suggests at least

some gene flow between populations in these rivers. Further study is necessary prior to

assessing the actual Altamaha River component both in the Ogeechee and other

adjacent rivers.

POPAN-5 is capable of estimating abundance, survival and capture probability and

was chosen because the field data best fit the program. The primary limitation of

POPAN is that because the numbers of individuals not captured are also estimated, the

parameter N includes unknown covariates. Therefore, covariates were not considered

when calculating the population estimate in this study. The best-fitting model in this

study assumed temporal variation in survival and recapture probabilities and constant

immigration. Although these assumptions may have been met, low recapture rates had

a considerable affect on the model and caused the model fit to decrease somewhat.

The Schnabel models used in this study assumed a closed population during each

sampling period. This assumption was probably not met given the movements of radio

tagged fish I observed. Furthermore, the estimates from the Schnabel model varied

widely — 46% lower to 30% higher than those generated by the POPAN model, which

suggests that management agencies should not use the simpler Schnabel model for

monitoring future population trends.

Population Age Structure

Age and Growth

In recent years, the marginal pectoral fin ray has become the preferred structure for

estimating the age of sturgeon because of the apparent non-lethality of this technique

63

and because cross sections from it are easier to interpret than those from other calcified

structures (e.g., otoliths or scutes) (Currier 1951, Pycha 1956, Roussow 1957, Dadswell

1979, Brennan and Cailliet 1989, Dovel et al. 1989, Keenlyne and Jenkins 1993, Rien

and Beamesderfer 1994, Morrow et al. 1998). In sturgeons, these rays contain

alternating opaque and translucent bands formed by the differences in summer and

winter growth rates (Currier 1951, Roussow 1957, Dadswell 1979, Nakamoto et al.

1995, LeBreton and Beamish 2000, Paragamian and Beamesderfer 2003). The dark

bands are created by rapid deposition of connective tissue during the summer

(Nakamoto et al. 1995) whereas the translucent bands are formed during the period of

metabolic inactivity that typically occurs during the winter when growth is slow, and

mineralization of the ray is relatively poor (Chilton and Beamish 1982, Nakamoto et al.

1995). Within a typical sturgeon fin ray, the growth increments appear as consistently

spaced rings formed throughout the juvenile phase. After maturity, however, growth

slows causing the growth annuli to become more closely spaced (Dadswell 1979,

Dadswell et al. 1984). This pattern of progressive “tightening” of the annuli in adult

sturgeon often makes interpretation of growth increments more difficult in older

specimens (Dadswell 1979, Dovel et al. 1989, Nakamoto et al. 1995, Fleming et al.

2003).

Age determination of individuals in this study proved difficult, and independent

observers regularly reported different initial age estimates from the same fin ray cross-

section. The age estimates were relatively precise and were comparable to other long-

lived species (Table 4.1). Coefficient of variance is an unbiased estimator of precision

64

Table 4.1. Coefficient of variance (CV) of age estimates for between-observer precision

for reported long-lived species.

Species CV Maximum observed age

White sturgeon A. transmontanus 1 7.8 104

Atlantic sturgeon A. oxyrinchus 2 4.8 42

Shortnose sturgeon A. brevirostrum 3 4.6 14

Monkfish Lophius vomerinus 4 6.3 11

Pacific ocean perch Sebastes alutus 5 4.9 78

Pacific hake Merluccius asper 5 3.2 16

Thorny skate Amblyraja radiata 6 2.8 16

Northern pike Esox luscius 7 1.2 11

Source: (1) Rien and Beamesderfer (1994); (2) Stevenson and Secor (1999); (3) this

study; (4) Maartens et al. (1999); (5) Kimura and Lyons (1991); (6) Sulikowski et al.

(2005); (7) Laine et al. (1991)

65

and allows comparison among species (Rien and Beamesderfer 1994). Among

reported values for 8 other species, 4 had higher values for CV than my study.

Difficulty in estimating age based on fin rays is not uncommon (Kohlhurst et al. 1980,

Rien and Beamesderfer 1994, Nakamoto et al. 1995, Morrow et al. 1998, Fleming et al.

2003). Several authors have questioned the validity of estimating the age of sturgeons

based on the first pectoral fin ray, citing either low accuracy or an underestimation of

age based on fish of known age (Rien and Beamesderfer 1994, Paragamian and

Beamesderfer 2003, Hurley et al. 2004, Whiteman et al. 2004). Numerous studies of

North American sturgeons; however, have used this method; Beamish and McFarlane

(1983); Rossiter et al. (1995) for lake sturgeon A. fulvescens, Brennan and Caillet

(1991), Rien and Beamesderfer (1994), and Paragamian and Beamesderfer (2003) for

white sturgeon A. transmontanus, Stevenson and Secor (1999) for Atlantic sturgeon A.

oxyrinchus, and Hurley et al. (2004) for pallid sturgeon Scaphirhynchus albus. For

shortnose sturgeon, some studies using stocked fish or mark-recapture experiments

have attempted to validate the method (Fleming et al. 2003, Paragamian and

Beamesderfer 2003). Age validation was not possible in this study because known age

fish were not available. Despite these difficulties, age determinations from the marginal

fin ray method provide the best non-lethal means available to obtain information on

growth, recruitment, and mortality of shortnose sturgeon.

The current age structure of the shortnose sturgeon population of the Altamaha

River suggests that individuals from southern populations may not be as long-lived as

their northern counterparts. Fleming et al. (2003) reached a similar conclusion

regarding shortnose sturgeon on the Ogeechee River, where he estimated maximum

66

age to be less than 16 years. Shortnose sturgeon from southern populations, also

appear to grow much faster than in northern rivers (Dadswell et al. 1984), as evident

from both this study and that of Fleming et al. (2003). Dadswell et al. (1984) suggests

that faster growth of shortnose sturgeon in southern rivers may be offset by smaller

maximum size; however, age and growth data from both the Altamaha and Ogeechee

rivers seem to disprove this theory. Individuals larger than 1000 mm TL were routinely

captured in this study, with the largest measuring 1166 mm TL.

The current size structure of the Altamaha shortnose sturgeon population may be

interpreted in several different ways. First, the relatively high abundance of juveniles

suggests that the population is recovering. If this is the case, then the number of adults

captured should increase and the numbers of juveniles gradually decrease with time as

the population approaches equilibrium. On the other hand, the data could suggest that

mortality between the juvenile and adult stages is unusually high, possibly a result of

incidental mortality associated with the commercial shad fishery and the simultaneous

spawning migration of shortnose sturgeon. If this is the case, then the large 2001

cohort would become indistinguishable as they were harvested over the proceeding

years. Another possible interpretation is that adults are less constrained to the tidally

influenced portion of the river than are juveniles and therefore are underrepresented in

my catch data. Capture data from 2003-2005 indicates that at most, 40% of the

resident population are adults; a potential increase of 30% from results reported by

Flournoy et al. (1992).

The catch curves used to derive the mortality estimates of shortnose sturgeon in this

study were based on several assumptions: 1) mortality was constant across the

67

sampling periods, 2) recruitment was constant across the sampling periods, 3) that

mortality was equal among ages, and 4) that all age/size classes were adequately

represented within the sample. The age-frequency histogram indicates that the latter

two assumptions may not have been met. A potential source of bias in the catch curve

data was the low sample size of fish older than age-10. A larger sample size of adults

might have resulted in a lower mortality estimate. By representing older cohorts, a more

representative distribution of adult size classes relative to age could have elevated the

right side of the catch curve, thereby decreasing the angle of the regression line and

subsequent mortality estimate. While I can not discount the possibility that adult

shortnose sturgeon were inhabiting areas where I did not sample, the lack of samples of

older fish was likely a result of a lack of those individuals within the population rather

than a result of sampling bias. Other large fish captured during the course of this study,

as well as reported preferred habitat in other studies on southern rivers (Flournoy et al.

1992, Weber 1996, Collins et al. 2001) is further evidence that adults are not as

abundant in the Altamaha river population. In 2005, an unusually large 2001 cohort

began to affect the mortality rate estimates by artificially inflating the portion of the curve

represented by age-4 fish. The violation of the assumption of constant recruitment may

have resulted in a higher mortality estimate in 2005. When age-4 fish were excluded

from the catch curve analysis the mortality rate slightly decreased from 0.384 to 0.344.

Given that shortnose sturgeon are long-lived and that the population has been

protected for over 30 years, I believe that adults should have been found in higher

numbers. Telemetry data indicated that although adults do make long spawning runs

into the upper reaches of the river where I did not sample, they did not spend much time

68

there outside of the spawning season, presumably because they prefer the tidally

influenced habitats of the lower river. Similar behavior for shortnose sturgeon also has

been documented in other studies in southern rivers (Collins and Smith 1993, Rogers

and Weber 1994, Moser and Ross 1995, Weber et al. 1998). Therefore, I believe my

data are reasonably representative of the current age-structure and that a particularly

strong year class may be the reason for the relatively high abundance of juveniles

observed in this study. A total annual mortality rate of about 30% is the highest ever

reported for any shortnose sturgeon population. In contrast, Secor and Woodland

(2005) reported a mortality rate of 22% for the Hudson River population.

Gear Selectivity

Several methods are used currently to sample sturgeon populations. Passive

entanglement gears often are the most effective, but they tend to be size selective

depending on the mesh sizes used and how they are deployed (Hamley 1975). This

bias is minimized most often by fishing “gangs” of different mesh sizes or by using

experimental nets that have been constructed using several mesh sizes (Hamley, 1975,

Kieffer and Kynard 1993, Foster and Clugston 1997, Haxton 2002). Direct selectivity

estimates can be derived through mark-recapture studies if the size distribution of the

population is known (Hamley 1975). In this study, however, I employed an indirect

method for estimating size selectivity because my recapture rate was low (9.6%) and

because the size distribution of the population was unknown. The indirect method that I

used required 2 assumptions. The first is that the degree of size selectivity depends on

the geometry of a fish relative to a specific mesh size as described by Baranov (1948).

69

Hence, the width of any given selectivity curve (i.e., the size range of fish captured by

any single mesh size) is proportional to the mesh size being fished (Hamley 1975). The

second assumption of the indirect method is that each mesh size used is equally

exposed to all fishes (Hovgård 1996). Because I used a variety of mesh sizes in

standardized nets that were deployed with equal effort in each period, this assumption

was met (Hovgård and Lassen 2000).

Because the population size-structure was unknown I standardized each selectivity

curve to 1 (Hamley 1975). However, this distorted the selectivity curve for each net,

especially for the 10.2 cm gill net. A total of 52 individuals were captured in this net,

and the length frequency histogram had 3 peaks occurring at 200 mm intervals, with

each peak comprised of only 5 fish. The effective range of fish sizes captured by the

10.2 cm gill net may be overstated by the curve. Because of the small number of

captures in this mesh size, the modes at 375 mm and again at 850 mm more likely

exaggerates the effective size range of fish captured by this mesh size. Given these

problems I used the combined catch of trammel nets and experimental gill nets in my

analysis of the population size-structure.

In comparing size distributions shortnose sturgeon captured in each gear type, I

found that trammel nets and experimental gill nets caught a slightly wider size

distribution of fish than did the 10.2 cm and 15.2 cm gill nets when fished in tandem.

The implications of this analysis are that single-mesh gill nets can be used to efficiently

sample specific size classes of sturgeon (e.g., juvenile cohorts), whereas experimental

gill nets and trammel nets provide a much more representative sample of the

population. Although this comparison showed that each gear may impart some size

70

selective bias to my catch data, the effect was probably not biologically significant.

Furthermore, the results suggest that using both trammel nets and experimental gill nets

may provide the best representation of the true population size.

Analysis of CPUE data from each gear type showed that trammel nets are more

efficient than gill nets. In 2005, I attempted to compensate for the disparity in the size

distribution between my trammel and single-mesh gill nets by fishing experimental gill

nets constructed from 3 different mesh sizes, but twice the number of these nets were

required to catch the same number of shortnose sturgeon as were caught in a single

trammel net. Furthermore, the smallest mesh in the experimental gill nets increased

bycatch to levels similar to those of trammel nets. This finding is noteworthy because a

primary argument against the use of trammel nets in fisheries sampling is that gill nets

are thought to produce less bycatch. Because site specific variables such as current

velocity and bottom structure may affect sampling efficiency of both gill and trammel

nets, sturgeon researchers should evaluate both types of gear in specific study areas

before implementing a long term sampling program.

Habitat and Seasonal Movements

Habitat Use in Summer

During summer months when water temperatures exceeded 27 oC, shortnose

sturgeon were not captured below the fresh-saltwater interface. All captures during this

time occurred in areas deeper than the surrounding river stretches, with a maximum

depth of 12.8 m. Similar habitats were used by shortnose sturgeon during the summer

on the Savannah River (Collins et al. 2001), Ogeechee River (Weber 1996) and in a

71

previous studies on the Altamaha River (Flournoy et al. 1992). In the latter study, the

authors postulated that deepwater habitats may contain coolwater springs that provide

important thermal refugia for shortnose sturgeon during the summer months. In this

study, however, we could detect no differences in bottom temperatures in the area

between rkm 22-23. Hence, I believe that the summer aggregation of shortnose

sturgeon in this area likely resulted from the combined effects of increasing temperature

and the progressive intrusion of the salt wedge that essentially “drove” shortnose

upstream to freshwater habitats. In fact, I observed the upstream movement of several

tagged fish into this area coincident with the progressive intrusion of the salt wedge.

Hence, I believe that summer aggregations of shortnose sturgeon at rkm 22-23 occur

simply because this area contains the first deepwater habitat above the salt wedge that

forms during summer, especially during periods of low discharge. Once the fish arrived

at this site, most remained there until water temperatures began to decline in late

summer or fall.

During the summer of 2005, water temperatures were 1-2 oC degrees cooler, and

discharge was much higher than in summer of 2004. Increased rainfall during the

summer months largely diminished the upstream intrusion of salt water in that year.

Not surprisingly, shortnose sturgeon were captured throughout the summer as far

downstream as rkm 15.4 and capture rates at rkm 22-23 were much lower than in

summer of 2004. Movements of radio-transmittered fish also showed that shortnose

moved freely throughout the lower portion of the river during summer 2005.

72

Habitat use in Fall, Winter, and Spring

Adult shortnose sturgeon actively moved throughout the river and estuary during the

cool months of the year. Areas of summer aggregations were abandoned by early fall

and individuals became scattered throughout the estuary. Captures of shortnose

sturgeon occurred over a variety of substrates (e.g., mud and sand) and at salinities of

0.0 - 26.1‰. Catches of more than 5 individuals were rarely obtained from any single

site, except in late January when 11 adults were captured at rkm 7-8. Subsequent

laparoscopic examination of these individuals revealed the presence of both gravid

females and ripe males. This aggregation of pre-spawning adults in the lower river

during late winter suggests that shortnose sturgeon may gather in specific estuarine

staging areas just prior to making their upstream spawning migrations. Although this

behavior has been documented previously for shortnose sturgeon on the Hudson River

(Bain et al. 2000), it has not been observed in a southern population and it has never

been found to occur in an estuarine environment. The importance of this behavior is

unknown; however, it may help to synchronize spawning migrations and the

reproductive cycles of males and females.

Spawning Habitat

Temperature appears to be a key environmental factor governing the timing of

spawning (Dadswell et al. 1984). Numerous studies from throughout the range of

shortnose sturgeon have shown that spawning occurs at temperatures between 9o and

12 oC (Meehan 1910, Heidt and Gilbert, 1978, Dadswell 1979, Taubert 1980a, Buckley

and Kynard 1981). This study documents the first confirmed spawn by shortnose

73

sturgeon in the Altamaha River. While water temperatures in the Altamaha at this time

were consistent with preferred spawning temperatures of shortnose sturgeon reported

in other studies, spawning substrates in the Altamaha were different than those

previously described. Substrates of both confirmed and suspected spawning sites of

shortnose sturgeon in this study typically consisted of course sand. Although Rogers

and Weber (1994) suggested that shortnose may spawn at nearby sites containing

large rock and gravel substrates, these areas were not found in this study. Although I

sampled substrates in several sites in the headwater reaches of the river, it is possible

that shortnose may spawn at several specific sites in this area of the river. Further

studies are needed to identify specific spawning habitats of shortnose sturgeon in this

area of the Altamaha System, including the lower reaches of both the Ocmulgee and

Oconee Rivers.

In northern rivers, spawning migrations appear to begin in late fall with individuals

overwintering just downstream of the spawning grounds (Dadswell 1979, Buckley

1982). In hypothesizing that this two-step migration pattern may also be used by

shortnose sturgeon in the Altamaha, Rogers and Weber (1994) suggested that

spawning adults may require additional time to accumulate the energy reserves needed

to make long upstream migrations. In this study, I did find congregations of pre-

spawning adults in the lower estuary during early winter, but their upstream migrations

were rapid and continuous once they began. Although two-step spawning migrations

can not be ruled out for Altamaha River shortnose sturgeon, this pattern was not

observed in this study or in previous studies of shortnose sturgeon in other southern

rivers (Hall et al. 1991, Collins and Smith 1993, Weber 1996).

74

Management Implications

This study has documented the largest known shortnose sturgeon population in the

southern United States. Based on the criteria specified by the Shortnose Sturgeon

Recovery Team (NMFS 1998), the Altamaha River population may be a possible

candidate for future delisting from the Federal Endangered Species List. Under the

terms of the Endangered Species Act, delisting of an endangered species (or a

population of that species) can be considered only when sufficient evidence exists that

the population is large enough to prevent extinction and that the loss of genetic diversity

is unlikely (NMFS 1998). Before any such action is considered, however, several

additional years of monitoring should be completed to ensure that the Altamaha

population maintains or increases its current abundance and complex age structure.

Although the results of this study have provided important new information about the

adult population of shortnose sturgeon in the Altamaha system, additional studies are

still needed to better understand recruitment mechanisms and habitat requirements of

juveniles. Furthermore, the minimum population size required to protect genetic

diversity has not been determined for any shortnose sturgeon population. Given that

southern populations exhibit a shorter life expectancy and are subject to greater

environmental stochasticity than their northern counterparts, delisting of any southern

population is probably premature at this time.

In Georgia, the commercial fishery for American shad operates on several coastal

rivers, including the Altamaha, from 1 January until the end of March. Because this

fishery coincides with annual spawning migrations of shortnose sturgeon, the incidental

75

take of spawning shortnose sturgeon could be substantial, especially where fishermen

employ bottom set gill nets. Previous studies by Collins et al. (1996) showed that

mortality of shortnose sturgeon captured in set gill nets was 16%; however, similar

studies in the Altamaha River have not been attempted

Illegal harvest of shortnose sturgeon is also a potential threat to the shortnose

sturgeon on the Altamaha River. Kynard (1997) reported that illegal harvest of

shortnose sturgeon in southern rivers was widespread and that 80% of radio-tagged fish

in the Cooper River (S.C.) were taken by poachers. Given that shortnose sturgeon

pass through many remote reaches of the Altamaha River during their annual spawning

migrations, additional studies are needed to quantify illegal harvest and to assess this

potential threat.

Summary

Data collected in this study shows that the Altamaha River population of shortnose

sturgeon is substantially larger than previously thought; however, the estimated

mortality rate raises concerns that undocumented sources of mortality may be limiting

further population growth. Growth rates of individual fish are higher than those reported

for northern populations but maximum lifespan is substantially shorter, although this

could be a result of anthropogenic factors. Unlike shortnose sturgeon in northern rivers,

adults exhibit one-step spawning migrations in the Altamaha from early January through

March. Spawning migrations, both upstream and downstream, are rapid and extensive

with most fish moving at least 200 rkm in each direction. After spawning, most adults

return to the brackish, or tidally influenced freshwater of the lower Altamaha. As

76

summer approaches and temperatures rise above 27 oC, the fish seek deep freshwater

habitats just upstream of the salt-freshwater interface. During periods of high water

temperature and low discharge, activity is reduced and the fish form large aggregations

in these deepwater areas

Based on the information obtained in this study, the shortnose sturgeon population of

the Altamaha River appears to be in the midst of a robust recovery. Although the

annual mortality rate of the population was surprisingly high, ~30%, the population

appears to be increasing as indicated by the relatively high abundance of juveniles

present in the catch data from both year of this study. Nonetheless, additional studies

are needed to identify and quantify potential threats from both legal and illegal fishing,

and to better understand factors that affect the abundance and survival of juvenile

shortnose sturgeon in this system.

77

LITERATURE CITED

Artyukhin, E.N. 1995. On biogeography and relationships within the genus Acipenser. Sturgeon Quarterly 3(2):6-7.

Auer, N.A. 1996. Importance of habitat and migration to sturgeons with

emphasis on lake sturgeon. Canadian Journal of Fisheries and Aquatic Science 53(1):152-160.

Bain, M.B. 1997. Atlantic and shortnose sturgeons of the Hudson River: common and divergent life history attributes. Evolutionary Biology of Fishes 48:347-358.

Bain, M.B, S. Nack, and J.G. Knight. 1995. Population status of shortnose

sturgeon in the Hudson River. Phase 1 Project Report to the U.S. Army Corps of Engineers, North Atlantic Division, New York, New York.

Baranov, F.I. 1948. Theory and assessment of fishing gear. Chapter 7

Theory of Fishing with Gillnets. Pishchepromizdat, Moscow. (in Russian) Bath, D.W., J.M. O’Connor, J.B. Albert, and L.G. Arvidson. 1981. Development

and identification of larval Atlantic sturgeon (Acipenser oxyrinchus) and shortnose sturgeon (A. brevirostrum) from the Hudson River estuary, New York. Copeia 1981(3):711-717.

Beamesderfer, R.C.P., and R.A. Farr. 1997. Alternatives for the protection and

restoration of sturgeons and their habitat. Environmental Biology of Fishes 48:407-417.

Beamish, R.J., and G.A. McFarlane. 1983. The forgotten requirement for age

validation in fisheries biology. Transactions of the American Fisheries Society 112:735-743.

Bemis, W.E., and B. Kynard. 1997. Sturgeon rivers: An introduction to

acipensiform biogeography and life history. Environmental Biology of Fishes 48:167-183.

Billard, R. and G. Lecointre. 2001. Biology and conservation of sturgeon and paddlefish. Reviews in Fish Biology and Fisheries 10:355-392.

Birstein, V.J. 1993. Sturgeons and Paddlefishes: threatened fishes in need of

conservation. Conservation Biology 7:773-787.

78

Birstein, V.J., R. Hanner, and R. DeSalle. 1997. Phylogeny of the

Acipenseriformes: cytogenetic and molecular approaches. Environmental Biology of Fishes 48:127-155.

Birstein, V.J., P. Doukakis, and R. DeSalle. 2002. Molecular phylogeny of

Acipenseridae: nonmonophyly of Scaphirhynchinae. Copeia 2:287-301. Blacklidge, K.H., and C.A. Bidwell. 1993. Three ploidy levels indicated by

genome quantification in Acipenseriformes of North America. Journal of Heredity 84:427-430.

Boreman, J., W.J. Overholtz, and D.B. Sissenwine. 1984. A preliminary

analysis of the effects of fishing on shortnose sturgeon. National Marine Fisheries Service, Northeast Fisheries Center. Woods Hole Laboratory Reference Document 84-17.

Brennan, J.S., and G.M. Cailliet. 1989. Comparative age-determination

techniques for white sturgeon in California. Transactions of the American Fisheries Society 118:296-310.

Buckley, J., and B. Kynard. 1981. Spawning and rearing of shortnose sturgeon

from the Connecticut River. The Progressive Fish-Culturist 43:74-76. Buckley, J. 1982. Seasonal movement, reproduction, and artificial spawning of

shortnose sturgeon (Acipenser brevirostrum) from the Connecticut River. M.S. Thesis, University of Massachusetts, Amherst, MA.

Buckley, J., and B. Kynard. 1985. Yearly movements of shortnose sturgeons in

the Connecticut River. Transactions of the American Fisheries Society 114:813-820.

Cameron, P., J. Berg, V. Dethefsen, and H. von Westernhagen. 1992.

Developmental defects in pelagic embryos of several flatfish species in the southern North Sea. Netherlands Journal of Sea Research 29(1-3):239- 256.

Campana, S.E., M.C. Annad, and J.I. McMillan. 1995. Graphical and statistical methods for determining the consistency of age determinations. Transactions of the American Fisheries Society124:131-138.

Carlson, D.M., and K.W. Simpson. 1987. Gut contents of juvenile shortnose

sturgeon in the upper Hudson estuary. Copeia 1987(3):769-802. Chang, W.Y. 1982. A statistical method for evaluating the reproducibility of age

determination. Canadian Journal of Fisheries and Aquatic Sciences

79

39:1208-1210. Chilton, D.E., and R.J. Beamish. 1982. Age determination methods for the

fishes studied by the ground-fish program at the Pacific Biological Station. Canadian Special Publication of Fisheries and Aquatic Sciences.

Choudhury, A., and T.A. Dick. 1998. The historical biogeography of sturgeons

(Osteichthyes: Acipenseridae): a synthesis of phylogenetics, palaeontology and palaeogeography. Journal of Biogeography 25:623- 640.

Cobb, J.N. 1900. The sturgeon fishery of Delaware River and Bay. Report of

the Commissioner, U.S. Commercial Fish and Fisheries 25:369-380. Collins, M.R., and T.I.J. Smith. 1993. Characteristics of the adult segment of

the Savannah River population of shortnose sturgeon. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife Agencies 47:485-491.

Collins, M.R., and T.I.J. Smith. 1996. Sturgeon fin ray removal is

nondeleterious. North American Journal of Fisheries Management 16:939- 941.

Collins, M.R., T.I.J. Smith, and L.D. Heyward. 1994. Effectiveness of six

methods for marking juvenile shortnose sturgeons. The Progressive Fish-Culturalist 56:250-254.

Collins, M.R., S.G. Rogers, and T.I.J. Smith. 1996. Bycatch of sturgeons along

the southern Atlantic coast of the USA. North American Journal of Fisheries Management 16:24-29.

Collins, M.R., and T.I.J. Smith. 1997. Distributions of shortnose and Atlantic

sturgeons in South Carolina. North American Journal of Fisheries Management 17:995-1000.

Collins, M.R., S.G. Rogers, T.I.J. Smith, and M.L. Moser. 2000. Primary

factors affecting sturgeon populations in the southeastern United States: fishing mortality and degradation of essential habitats. Bulletin of Marine Science 66(3):917-928.

Collins, M.R., W.C. Post, and D.C. Russ. 2001. Distribution of shortnose

sturgeon in the lower Savannah River. Final Report to Georgia Ports Authority 21 pp.

Collins, M.R., W.C. Post, D.C. Russ, and T.I.J. Smith. 2002a. Habitat use and

movements of juvenile shortnose sturgeon in the Savannah River,

80

Georgia-South Carolina. Transactions of the American Fisheries Society 131:975-979.

Collins, M.R., D.W. Cooke, T.I.J. Smith, W.C. Post, D.C. Russ, and D.C. Walling.

2002b. Evaluation of four methods of transmitter attachment on shortnose sturgeon, Acipenser brevirostrum. Journal of Applied Ichthyology 18:491-494.

Collins, M.R., D. Cooke, W.C. Post, J. Crane, J. Bulak, T.I.J. Smith, T.W. Greig,

and J.M. Quattro. 2003. Shortnose sturgeon in the Santee-Cooper Reservoir System, South Carolina. Transactions of the American Fisheries Society 132:1244-1250.

Cooke, D.W., and S.D. Leach. 2004. Implications of a migration impediment

on shortnose sturgeon spawning. North American Journal of Fisheries Management 24:1460-1468.

Cooke, D.W., J.P. Kirk, J.V. Morrow, and S.D. Leach. 2004. Population

dynamics if a migration limited shortnose sturgeon population. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife Agencies 58:82-91.

COSEWIC. 2005. COSEWIC assessment and update status report on the

shortnose sturgeon Acipenser brevirostrum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa.

Crance, J.H. 1986. Habitat suitability index models and instream flow suitability

curves: shortnose sturgeon. U.S. Fish and Wildlife Service Biological Report 82 (10.129).

Cuerrier, J.P. 1951. The use of pectoral fin rays for determining fish age of

sturgeon and other species of fish. Canadian Fish Culturist 11:10-18. Curran, H.W., and S.T. Reis. 1937. Fisheries investigations in the lower

Hudson River. In A biological survey of the lower Hudson watershed. Report to the New York State Conservation Department, Supp. 26:124- 145.

Dadswell, M.J. 1979. Biology and population characteristics of the shortnose

sturgeon, Acipenser brevirostrum LeSueur 1818 (Osteiichthyes: Acipenseridae), in the Saint john River Estuary, New Brunswick, Canada. Canadian Journal of Zoology 57:2186-2210.

Dadswell, M.J., B.D. Taubert, T.S. Squiers, D. Marchette, and J. Buckley. 1984.

Synopsis of biological data on shortnose sturgeon, Acipenser brevirostrum LeSueur 1818. FAO Fisheries Synopsis No. 40.

81

Dahlberg, M.D., and D.C. Scott. 1971. The freshwater fishes of Georgia. Bulletin of the Georgia Academy of Science 29:1-64.

Dovel, W.L., A.W. Pekovitch, and T.J. Berggren. 1989. Biology of the

shortnose sturgeon (Acipenser brevirostrum Lesueur, 1818) in the Hudson River estuary, New York. Pages 187-216 in C.L. Smith, ed. Estuarine Research in the 1980’s. State University of New York Press, Albany, New York.

Duncan, M.S., J.J. Isely, and D.W. Cooke. 2004. Evaluation of shortnose

sturgeon spawning in the Pinopolis Dam tailrace, South Carolina. North American Journal of Fisheries Management 24:932-938.

Dwyer, F.J., D.K. Hardesty, C.G. Ingersoll, J.L. Kunz, and J.W. Whites. 2000.

Assessing contaminant sensitivity of American shad, Atlantic sturgeon and shortnose sturgeon. U.S. Geological Survey Final Report. Columbia Missouri.

Dynesius, M., and C. Nilsson. 1994. Fragmentation and flow regulation of river

systems in the northern third of the world. Science 266:753-762. Findeis, E.K. 1997. Osteology and phylogenetic interrelationships of sturgeons

(Acipenseridae). Environmental Biology of Fishes 48:73-126. Fleming, J.E., T.D. Bryce, and J.P. Kirk. 2003. Age, growth, and status of

shortnose sturgeon in the lower Ogeechee River, Georgia. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife Agencies 57:80-91.

Flournoy, Phillip H., S. Gordon Rogers, and Paulette S. Crawford. 1992.

Restoration of shortnose sturgeon in the Altamaha River, Georgia. United States Fish and Wildlife Service Project Number AFS-2, Segments One and Two.

Fontana, F., R. Rossi, M. Lanfred, G. Arlati, and P. Bronzi. 1999. Chromosome

banding in sturgeons. Journal of Applied Ichthyology 15:9-11. Fontana, F., J. Tagliavini, and L. Congiu. 2001. Sturgeon genetics and

cytogenetics: recent advancements and perspectives. Genetica 111:359- 373.

Foster, A.M. and J.P. Clugston. 1997. Seasonal migration of Golf sturgeon in

the Suwannee River, Florida. Transactions of the American Fisheries Society 126:302-308.

Gardiner, B.G. 1984. Sturgeons as living fossils. Pages 148-152 in N.

82

Eldridge and S.M. Stanley, eds. Living Fossils. Springer-Verlag, New York. 291 pp.

Geoghegan, P., M.T. Mattson, and R.G. Keppel. 1989. Distribution of the

shortnose sturgeon in the Hudson River Estuary, 1984-1988. Pages 217- 227 in C.L. Smith, ed. Estuarine Research in the 1980’s. State University of New York Press, Albany, New York.

GEPD (Georgia Environmental Protection Division). 2003. Altamaha River

Basin Management Plan 2003. Georgia Department of Natural Resources, Atlanta.

Gerbilskiy, N.L. 1957. Ways of development of the intraspecies biological

differentiation, types of anadromous migrants, and a question of migration impulse in sturgeons. Uchenye Zapiski Leningradskogo Gosudarstvennogo Universiteta 228:11-31. (in Russian)

Gilbert, C.R. 1989. Species profiles: life histories and environmental

requirements of coastal fishes and invertebrates (Mid–Atlantic Bight) – Atlantic and shortnose sturgeons. U.S. Fish and Wildlife Service Biological Report 82 (11.122).

Hall, J.W., T.I.J. Smith, and S.D. Lamprecht. 1991. Movements and habitats

of shortnose sturgeon, Acipenser brevirostrum in the Savannah River. Copeia 3:695-702.

Hamley, J.M. 1975. Review of gillnet selectivity. Journal of the Fisheries

Research Board of Canada 32:1943-1969. Hardy, R.S., and M.K. Litvak. 2004. Effects of temperature on the early

development, growth, and survival of shortnose sturgeon, Acipenser brevirostrum, and Atlantic sturgeon Acipenser oxyrinchus, yolk-sac larvae. Environmental Biology of Fishes 70:145-154.

Hastings, R.W., J.C. O’Herron, K. Schick, and M.A. Lazzari. 1987. Occurrence

and distribution of shortnose sturgeon, Acipenser brevirostrum, in the upper tidal Delaware River. Estuaries 10:337-341.

Haxton, T. 2002. An assessment of lake sturgeon (Acipenser fulvescens) in

various reaches of the Ottawa River. Journal of Applied Ichthyology 18:449-454.

Heidt, A.R., and R.J. Gilbert. 1978. The shortnose sturgeon in the Altamaha

River drainage, Georgia. Pages 54-60 in R.R. Odum and L. Landers, editors. Proceedings of the rare and endangered wildlife symposium. Georgia Department of Natural Resources, Game and Fish Division,

83

Technical Bulletin WL 4, Athens, Georgia. Hernandez-Divers, S.J., R.S. Bakal, B.H. Hickson, C.A. Rawlings, H.G. Wilson,

M. Radlinsky, S.M. Hernandez-Divers, and S.R. Dover. 2004. Endoscopic sex determination and gonadal manipulation in Gulf of Mexico sturgeon (Acipenser oxyrinchus desotoi). Journal of Zoo and Wildlife Medicine 35(4):459-470.

Hoff, T.B., R.J. Klauda, and J.R. Young. 1988. Contribution to the biology of

shortnose sturgeon in the Hudson River Estuary. Pages 171-189 in C.L. Smith Editor. Fisheries Research in the Hudson River. Hudson River Environmental Society. State University of New York Press, Albany.

Hovgård, H. 1996. A two-step approach to estimating selectivity and fishing

power or research gill nets used in Greenland waters. Canadian Journal of Fisheries and Aquatic Sciences 53:1007-1013.

Hovgård, H, and H. Lassen. 2000. Manual on estimation of selectivity for gillnet

and longline gears in abundance surveys. FAO Fisheries Technical Paper No. 397, Rome. 84 pp.

Hurley. K.L., R.J. Sheehan, and R.C. Heidinger. 2004. Accuracy and precision

of age estimates for pallid sturgeon from pectoral rays. North American Journal of Fisheries Management 24:715-718.

Jarvis, P.L., J.S. Ballantyne, and W.E. Hogans. 2001. The influence of salinity

on the growth of juvenile shortnose sturgeon. North American Journal of Aquaculture 63:272-276.

Jenkins, W.E., T.I.J. Smith, L.D. Heyward, and D.M. Knott. 1993. Tolerance of

shortnose sturgeon, Acipenser brevirostrum, juveniles to different salinity and dissolved oxygen concentrations. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife Agencies 47:476-484.

Keenlyne, K.D., and L.G. Jenkins. 1993. Age at maturity of the pallid sturgeon. Transactions of the American Fisheries Society 122:393-396.

Kieffer, M.C., and B. Kynard. 1993. Annual movements of shortnose and

Atlantic sturgeons in the Merrimack River, Massachusetts. Transactions of the American Fisheries Society 122:1088-1103.

Kieffer, M.C., and B. Kynard. 1996. Spawning of the shortnose sturgeon in the

Merrimack River, Massachusetts. Transactions of the American Fisheries Society 125:179-186.

84

Kim, D.S., Y.K. Nam, J.K. Noh, C.H. Park, and F.A. Chapman. 2005. Karyotype of North American shortnose sturgeon Acipenser brevirostrum with the highest chromosome number in Acipenseriformes. Ichthyological Research 52:94-97.

Kimura, D.K., and J.J. Lyons. 1991. Between-reader bias and variability in the age

determination process. U.S. National Marine Fisheries Service Fishery Bulletin 89:53-60.

Klyszejko, B., Z. Chelkowski, B. Chelkowska, and A. Sobocinski. 2004.

Identification of fish remains from early-mediaeval layers of the vegetable market excavation site in Szczecin, Poland. Acta Ichthyologica et Piscatoria 34(1):85-102.

Kohlhorst, D.W. 1979. Effect of first pectoral ray removal on survival and

estimated harvest rate of white sturgeon in the Sacramento-San Joaquin estuary. California Fish and Game 65:173-177.

Kohlhorst, D.W., L.W. Miller, and J.J. Orsi. 1980. Age and growth of white sturgeon

collected in the Sacramento-San Joaquin Estuary, California: 1965-1970 and 1973-1976. California Fish and Game 66:83-95.

Krieger, J., P.A. Fuerst, and T.M. Cavender. 2000. Phylogenetic relationships

of the North American sturgeons (Order Acipenseriformes) based on mitochondrial DNA sequences. Molecular Phylogenetics and Evolution 16(1):64-72.

Kynard, B. 1997. Life history, latitudinal patterns, and status of the shortnose

sturgeon, Acipenser brevirostrum. Environmental Biology of Fishes 48:319-334.

Kynard, B. 1998. Twenty-two years of passing shortnose sturgeon in fish lifts

on the Connecticut River: What has been learned? Pages 255-266 in S.S.M. Jungwirth and S. Weiss, eds. Fish Migration and Fish Bypasses. Fishing News Books, Oxford.

Kynard, B., M. Kieffer, M. Burlingame, and M. Horgan. 1999. Studies on shortnose

sturgeon, 1999. Final Report to Northeast Utilities Service Co., Berlin, Connecticut.

Kynard, B., M. Horgan, M. Kieffer, and D. Seibel. 2000. Habitats used by

shortnose sturgeon in two Massachusetts rivers, with notes on estuarine Atlantic sturgeon: A hierarchical approach. Transactions of the American Fisheries Society 129:487-503.

Kynard, B., and M. Horgan. 2002. Ontogenetic behavior and migration of

85

Atlantic sturgeon Acipenser oxyrinchus, and shortnose sturgeon, A. brevirostrum, with notes on social behavior. Environmental Biology of Fishes 63:137-150.

Laine, A.O., W.T. Momot, and P.A. Ryan. 1991. Accuracy of using scales and cleithra

for aging northern pike from an oligotrophic Ontario Lake. North American Journal of Fisheries Management 11:220-225.

LeBreton, G.T.O., and F.W.H. Beamish. 2000. Suitability of lake sturgeon

growth rings in chronology development. Transactions of the American Fisheries Society 129:1018-1030.

LeSueur, C.A. 1818. Description of several species of Chondropterygious

fishes in North America, with their varieties. Transactions of the American Philosophical Society 1:383-395.

Longwell, A.C., S. Chang, A. Hebert, J. Hughes, and D. Perry. 1992. Pollution

and developmental abnormalities of Atlantic fishes. Environmental Biology of Fishes 35:1-21.

Ludwig, A., N.M. Belfiore, C.Pitra, V.Svirsky, and I. Jenneckens. 2001.

Genome duplication events and functional reduction of ploidy levels in sturgeon (Acipenser, Huso, and Scaphirhynchus). Genetics 158:1203- 1215.

Maartens, L., A.J. Booth, and T. Hecht. 1999. The growth of monkfish Lophius vomerinus in Nambian waters, with a comparison of otoliths and illicia methods of ageing. Fisheries Research 44:139-148.

Marchette, D.E., and R. Smiley. 1982. Biology and life history of incidentally

captured shortnose sturgeon, Acipenser brevirostrum in South Carolina. South Carolina Wildlife and Marine Resources. Unpublished MS.

Markov, K.P. 1978. Adhesiveness of egg membranes in sturgeons (Family

Acipenseridae). Journal of Ichthyology 18:437-446. Mason Jr., W.T., and J.P. Clugston. 1993. Foods of the Gulf sturgeon in the

Suwannee River, Florida. Transactions of the American Fisheries Society 122:378-385.

McCleave, J.D., S.M. Fried, and A.K.Towt. 1977. Daily movements of

shortnose sturgeon, Acipenser brevirostrum, in a Maine estuary. Copeia 1:149-157.

Meehan, W.E. 1910. Experiments in sturgeon culture. Transactions of the

American Fisheries Society 39:85-91.

86

Morrow, J.V., J.P. Kirk, K.J. Killgore, and S.G. George. 1998. Age, growth, and

mortality of shovelnose sturgeon in the lower Mississippi River. North American Journal of Fisheries Management 18:725-730.

Moser, M. L., and S.W. Ross. 1995. Habitat use and movements of shortnose

and Atlantic sturgeons in the lower Cape Fear River, North Carolina. Transactions of the American Fisheries Society 124:225-234.

Moser, M.L., M. Bain, M.R. Collins, N. Haley, B. Kynard, J.C. O’Herron II, G.

Rogers, and T.S. Squiers. 2000. A protocol for use of shortnose and Atlantic sturgeons. NOAA Technical Memorandum NMFS-OPR-18.

Murawski, S.A., and A.L. Pacheco. 1977. Biological and fisheries data on the

Atlantic sturgeon, Acipenser oxyrhinchus (Mitchill). U.S. National Marine Fisheries Service, Technical Series Report 10, Highlands, New Jersey.

Nakamoto, R.J., T.T. Kisanuki, and G.H. Goldsmith. 1995. Age and growth of

Klamath River green sturgeon (Acipenser medirostris). U.S. Fish and Wildlife Service Project No. 93-FP-13. 20 pp.

National Marine Fisheries Service. 1998. Recovery plan for the shortnose

sturgeon (Acipenser brevirostrum). Prepared by the Shortnose Sturgeon Recovery Team for the National Marine Fisheries Service, Silver Spring, Maryland 104 pp.

O’Herron II, J.C., K.W. Able, and R.W. Hastings. 1993. Movements of

shortnose sturgeon (Acipenser brevirostrum) in the Delaware River. Estuaries 16(2):235-240.

Palmer, A.G. 2001. Seasonal, diel, and tidal movements of shortnose

sturgeon, Acipenser brevirostrum, in the Cooper River, South Carolina. Master’s Thesis. University of Charleston, Charleston, South Carolina.

Paragamian, V.L., and R.C.P. Beamesderfer. 2003. Growth estimates from

tagged white sturgeon suggest that ages from fin rays underestimate true age in the Kootenai River, USA and Canada. Transactions of the American Fisheries Society 132:895-903.

Parsons, G.R., J.J. Hoover, and K.J. Killgore. 2003. Effect of pectoral fin ray

removal on station-holding ability of shovelnose sturgeon. North American Journal of Fisheries Management 23:723-747.

Pekovitch, A.W. 1979. Distribution and some life history aspects of the

shortnose sturgeon (Acipenser brevirostrum) in the upper Hudson River estuary. Hazelton Environmental Science Corp., Northbrook, IL.

87

Pycha, R.L. 1956. Progress report on white sturgeon studies. California Fish

and Game 42:23-35. Quattro, J.M. T.W. Greig, D.K. Coykendall, B.W. Bowen, and J.D. Baldwin.

2002. Genetic issues in aquatic species management: the shortnose sturgeon (Acipenser brevirostrum) in the southeastern United States. Conservation Genetics 3:155-166.

Richmond, A.M., and B. Kynard. 1995. Ontogenetic behavior of shortnose

sturgeon, Acipenser brevirostrum. Copeia 1:172-182. Ricker, W.E. 1975. Computation and interpretation of biological statistics of

fish populations. Bulletin of Fisheries Research of the Board of Canada 191. 382 pp.

Rien, T.A., and R.C. Beamesderfer. 1994. Accuracy and precision of white

sturgeon age estimates from pectoral fin rays. Transactions of the American Fisheries Society 123:255-265.

Ritchie, W.A. 1969. The archaeology of Martha’s Vineyard. The Natural

History Press, Garden City, New York. 253 pp. Rogers, S.G., and W. Weber. 1994. Movements of shortnose sturgeon in the

Altamaha River System, Georgia. Contributions Series No. 57. Coastal Resources Division, Georgia Department of Natural Resources, Brunswick, Georgia.

Rogers S.G., P.H. Flournoy, and W. Weber. 1994. Status and restoration of

Atlantic sturgeon in Georgia. Final Report to the National Marine Fisheries Service, Southeast Regional Office, St. Petersburg, Florida.

Rogers, S.G., and W. Weber. 1995. Status and restoration of Atlantic and

shortnose sturgeons in Georgia. Final Report to the National Marine Fisheries Service, Southeast Regional Office, St. Petersburg, Florida.

Rossiter, A., D.L.G. Nokes, and F.W.H. Beamish. 1995. Validation of age

estimation for the lake sturgeon. Transactions of the American Fisheries Society 124:777-781.

Ruelle, R., and K.D. Keenlyne. 1993. Contaminants in Missouri River pallid

sturgeon. Bulletin of Environmental Contamination and Toxicology 50:898-906.

Russow, G. 1957. Some considerations concerning sturgeon spawning

periodicity. Journal of the Fisheries Research Board of Canada 14:553-

88

572. Ryder, J.A. 1890. The sturgeons and sturgeon industries of the eastern coast

of the United States, with an account of experiments bearing upon sturgeon culture. Bulletin of the U.S. Fisheries Commission 8:231-328.

Scott, W.B., and E.J. Crossman. 1973. Freshwater Fishes of Canada.

Bulletin 184, Fisheries Research Board of Canada, Ottawa. 966 pp. Secor, D.H., and R.J. Woodland. 2005. Recovery and status of shortnose

sturgeon in the Hudson River. Hudson River Foundation for Science and Environmental Research, Inc. 105 pp.

Sindermann, C.J. 1979. Pollution-Associated Diseases and Abnormalities of

Fish and Shellfish: A Review. Fishery Bulletin 76(4):717-749. Smith, T.I.J., D.E. Marchette, and G.F. Ulrich. 1984. The Atlantic sturgeon

fishery in South Carolina. North American Journal of Fisheries Management 4:164-176.

Smith, T.I.J., S.D. Lamprecht, and J.W. Hall. 1990. Evaluation of tagging

techniques for shortnose sturgeon and Atlantic sturgeon. American Fisheries Society Symposium 7:134-141.

Smith, T.I.J., and M.R. Collins. 1996. Shortnose sturgeon stocking success in

the Savannah River. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife Agencies 50:112-121.

Smith, T.I.J., J.W. McCord, M.R. Collins, and W.C. Post. 2002. Occurrence of

stocked shortnose sturgeon Acipenser brevirostrum in non-target rivers. Journal of Applied Ichthyology 18:470-474.

Squiers, T.S., M. Smith, and L. Flagg. 1982. American shad enhancement and

status of sturgeon stocks in selected Maine waters. Final Report to the National Marine Fisheries Service, Gloucester, Massachusetts.

Stevenson, J.T., and D.H. Secor. 1999. Age determination and growth of

Hudson River Atlantic sturgeon, Acipenser oxyrinchus. Fisheries Bulletin 97:153-166.

Sulikowski, J.A., J. Kneebone, S. Elzey, J. Jurek, P.D. Danley, W.H. Howell, and

P.C.W. Tsang. 2005. Age and growth estimates of the thorny skate (Amblyraja radiata) in the western Gulf of Maine. Fisheries Bulletin 103:161-168.

Taubert, B.D. 1980a. Reproduction of the shortnose sturgeon (Acipenser

brevirostrum) in the Holyoke Pool, Connecticut River, Massachusetts.

89

Copeia 1980:114-117. Taubert, B.D. 1980b. Biology of the shortnose sturgeon (Acipenser

brevirostrum) from the Holyoke Pool, Connecticut River, Massachusetts, USA. Ph.D. Dissertation, University of Massachusetts, Amherst.

Taubert, B.D., and M.J. Dadswell. 1980. Description of some larval shortnose

sturgeon (Acipenser brevirostrum) from the Holyoke Pool, Connecticut River, MA, USA, and the St. John River, NB, Canada. Canadian Journal of Zoology 58:1125-1128.

Trencia, G., G. Verreault, S. Georges, and P. Pettigrew. 2002. Atlantic

sturgeon (Acipenser oxyrinchus oxyrinchus) fishery management in Québec, Canada, between 1994 and 2000. Journal of Applied Ichthyology 18:455-462.

van den Avyle, M.J. 1984. Species profiles: life histories and environmental

requirements of coastal fishes and invertebrates (south Atlantic)—Atlantic sturgeon. U.S. Fish and Wildlife Service Biological Report 81 (11.25).

Vladykov, V.D., and J.R. Greeley. 1963. Order Acipenseroidei. Pages 24-60

in V.H. Olsen, editor. Fishes of the western North Atlantic, part III. Memoirs of the Sears Foundation for Marine Research, New Haven Connecticut. 630 pp.

Waldman, J.R., C.Grunwald, J. Stabile, and I. Wirgin. 2002. Impacts of life history and biogeography on the genetic stock structure of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus, Gulf sturgeon A. oxyrinchus desotoi, and shortnose sturgeon A. brevirostrum. Journal of Applied Ichthyology 18(2002): 509-518.

Walsh, M.G., M.B. Bain, T. Squiers Jr., J.R. Waldman, and I. Wirgin. 2001. Morphological and genetic variation among shortnose sturgeon Acipenser brevirostrum from adjacent and distant rivers. Estuaries 24(1): 41-48.

Wang, Y.L., F.P. Binkowski, S.I. Doroshov. 1985. Effect of temperature on

early development of white and lake sturgeon, Acipenser transmontanus and A. fulvescens. Environmental Biology of Fishes 14(1):43-50.

Weber, W. 1996. Population size and habitat use of shortnose sturgeon,

Acipenser brevirostrum, in the Ogeechee River system, Georgia. M.S. Thesis, University of Georgia, Athens, Georgia.

Weber, W., C.A. Jennings, and S.G. Rogers. 1998. Population size and

movement patterns of shortnose sturgeon in the Ogeechee River system, Georgia. Proceedings of the Annual Conference of the Southeast

90

Association of Fish and Wildlife Agencies 52: 18-28. Welsh, S.A., M.F. Mangold, and S.M. Eyler. 2001. Movement of shortnose

sturgeon in the Upper Chesapeake Bay, Maryland. Proceedings of the Annual Conference of the Southeast Association of Fish and Wildlife Agencies 55:298-303.

Whiteman, K.W., V.H. Travnichek, M.L. Wildhaber, A. DeLonay, D. Papoulias,

and D. Tillett. 2004. Age estimation for shovelnose sturgeon: A cautionary note based on annulus formation in pectoral fin rays. North American Journal of Fisheries Management 24:731-734.

Williams, B.K., J.D. Nichols, and M.J. Conroy. 2002. Analysis and

Management of Animal Populations. Academic Press, San Diego, California. 817 pp.

Winter, J.D. 1983. Advances in underwater biotelemetry. Pages 555-590 in

B.R. Murphy and D.W. Wells, eds. Fisheries Techniques. American Fisheries Society, Bethesda, Maryland. 732 pp.

Wirgin, I., C. Grunwald, E. Carlson, J. Stabile, D.L. Peterson, and J. Waldman.

2005. Range-wide population structure of shortnose sturgeon Acipenser brevirostrum based on sequence analysis of the mitochondrial DNA control region. Estuaries 28(3):406-421.

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