REVIEW PAPER Responsible estuarine finfish stock

REVIEW PAPER

Responsible estuarine finfish stock enhancement: an

Australian perspective

M. D. TAYLOR*†, P. J. PALMER‡, D. S. FIELDER§ AND

I. M. SUTHERS*

*School of Biological, Earth and Environmental Science, University of New SouthWales, 2052, Australia, ‡Bribie Island Aquaculture Research Centre, QueenslandDepartment of Primary Industries and Fisheries, Woorim, Queensland, 4507,

Australia and §Port Stephens Fisheries Centre, New South Wales Department ofPrimary Industries, Taylors Beach, New South Wales, 2316, Australia

(Received 19 July 2004, Accepted 1 March 2005)

The responsible approach to marine stock enhancement is a set of principles aimed at maximising

the success and benefits of artificially re-stocking depleted fisheries. The benefits of such an

approach are evident in the 400% increase in survival of stocked striped mullet in Hawaii through

refinement of release techniques, however financially or temporally constrained stocking pro-

grams in Australia have not adhered to all principles. A pragmatic approach to address these

principles is proposed, using international examples and Australian marine finfish pilot stockings

of barramundi, mulloway, sand whiting, dusky flathead and black bream. Biological ranking of

candidate species by estuarine residency, a low natural-mortality to growth ratio, a large L1 and

comparison by recreational value and available rearing technologies, show that mulloway,

barramundi and sea mullet are ideal species for stocking in Australia. Australian intermittently

closed opening landlocked lagoons and recreational fishing havens, especially near cities, provide

experimental opportunities to apply this approach and stock suitable species through small-scale

pilot experiments. This would allow evaluation of production and carrying capacity, and density

dependent processes with respect to optimal stocking strategies unconfounded by emigration and

commercial fishing practices. Twenty per cent of Australians fish each year, and harvest approxi-

mately 27 000 t of finfish. Stocking recreationally important species in Australia should give a

greater financial benefit, which is spread across a larger cross-section of the community, com-

pared to stocking to enhance commercial fisheries. The pragmatic application of the responsible

approach, and stocking of fast growing estuarine residents into recreational fishing havens would

enhance the benefit from marine stocking. # 2005 The Fisheries Society of the British Isles

Key words: estuary; finfish; recreational fishing; responsible approach; stock enhancement.

INTRODUCTION

Fisheries managers may seek stock enhancement to restore depleted popula-tions of recreationally and commercially significant fish species (Masuda &Tsukamoto, 1998; McEachron et al., 1998; Svasand, 1998). Stock enhancement

†Author to whom correspondence should be addressed. Tel.: þ612 9385 2118; fax: þ612 9385 1558;

email: [email protected]

Journal of Fish Biology (2005) 67, 299–331

doi:10.1111/j.1095-8649.2005.00809.x,availableonlineathttp://www.blackwell-synergy.com

299# 2005TheFisheries Society of theBritish Isles

of marine species is a controversial method of fisheries management fromeconomic (Hilborn, 1998), genetic (Utter, 1998) and environmental (Cooney& Brodeur, 1998) perspectives, and gains made from stock enhancement maynot be sustainable (Leber, 1999). Nevertheless, there is significant recreationalfishing interest in stock enhancement (Hilborn, 1999; Huggan, 2001), and theapproach is politically preferable to introducing harsher and less popularconservation measures, such as catch and gear restrictions (Travis et al.,1998). In Australia, the lack of any substantial upwelling (Rochford, 1979)means that nutrient input from estuaries may represent a large proportion oftotal production. This, coupled with the demonstrated lack of success in stock-ing oceanic species (Hilborn, 1998; Svasand et al., 2000), indicates that stockenhancement in Australia should be confined to estuaries and estuarineresidents.Many fish species use estuarine habitats for all or part of their life cycle, and in

many cases estuaries are essential for completing a stage of a species life history(Blaber, 1997; Costello et al., 2002). This estuarine dependence is largely aresponse to the availability of food in estuaries that is absent in offshore waters,and the presence of complex habitats such as mangroves and seagrass to provideshelter from predation and adverse physical conditions for smaller fish (Blaber,1997). The provision of habitat, and productivity within estuaries has led toongoing recreational, commercial and subsistence fisheries worldwide, howevermany estuaries have been adversely affected by pollution, land reclamation andthe reduction of fish passage through dam building (Cattrijsse et al., 2002). Theflow-on effects from these and other impacts like stocking and habitat restora-tion are not only relevant for estuarine residents. Those oceanic species that useestuaries throughout their life, such as pilchards Sardinops sagax neopilchardis(Steindachner) and anchovy Engraulis australis (White) (Kailola et al., 1992) willalso be affected by activities undertaken in estuaries.Blankenship & Leber (1995) propose a ten-step responsible approach to

marine stock enhancement (Table I), that encourages the application of small-scale experiments. Due to the highly variable nature of the marine environmentthese experiments are best confined to estuaries. The benefits of such anapproach are evident in the successful stock enhancement of sea-mullet Mugilcephalus (Linnaeus) in Hawaii (Leber, 1999) and red-drum Sciaenops ocellatus(Linnaeus) in Texas (McEachron & Daniels, 1995). Whilst some propose furtherscientific evaluation of stock enhancement technology (Hilborn, 1999) andadvocate that it can be used responsibly (Blankenship & Leber, 1995), othersclassify the approach as techno-arrogant and a halfway technology (Frazer,1992; Meffe, 1992). Despite these criticisms, estuarine stock enhancement canbe a stop-gap measure, and can potentially be used to temporarily supplementrecruitment until habitat restoration and stock rebuilding can occur. Habitatrestoration may never satisfactorily occur in ports, harbours and other urbanizedareas, and in this case stock enhancement may be one pragmatic approach toaddress declining fish stocks. Successful use of stock enhancement in the futurerelies on a responsible and cautious approach. Large scale economic and biolo-gical failures from stocking programs, such as the salmonid programs in thePacific Northwest (Hilborn, 1998), show that this should be achieved in astepwise fashion guided by small-scale research projects to reveal the underlying

300 M. D. TAYLOR ET AL .

# 2005 The Fisheries Society of the British Isles, Journal of Fish Biology 2005, 67, 299–331

mechanisms of stock dynamics and resolve any effect stocking may have.Combining a responsible approach with a sound knowledge of the dynamicsand productive capacity of the target ecosystem will help ensure that appropriatespecies are stocked and sustained by the environment. By drawing on the

TABLE I. Responsible approach to developing, appraising and managing marine stockenhancement proposed by Blankenship & Leber (1995)

Principles

1) Prioritize and select target species for enhancement

� Initial workshop to define and rank selection criteria

� Community survey to solicit opinions on selection criteria and identify candidatespecies

� Rank candidate species with respect to selection criteria and seek consensus fromstakeholders on most appropriate species

2) Develop a species management plan

� Identify harvest opportunity, stock rebuilding goals and genetic objectives

� Consider goals and objectives in the context of the management plan for candidatespecies

� Evaluate strategies to use in conjunction with stock enhancement3) Define quantitative measures of success

� Develop benchmarks against which to measure enhancement success

� Benchmarks should relate to stock rebuilding goals and genetic objectives4) Use genetic resource management

� Identify the genetic risks and consequences of enhancement

� Define an enhancement strategy

� Outline research needs and objectives

� Develop a feedback mechanism

� Implement genetic controls in the hatchery and a monitoring and evaluation pro-gram for wild stocks

5) Use disease and health management

� Adopt responsible hatchery practice

� Certify fish are free from viral, parasitic and bacterial infections6) Form enhancement objectives and tactics

� Evaluate stock enhancement in an ecological context

� Evaluate behavioural and physiological deficiencies that may be present in stocked fish7) Identify released fish and assess stocking effects

� Develop efficient methods for marking fish

� Evaluate interactions between hatchery fish and wild stocks and competitors8) Use an empirical process for defining optimum release strategies

� Optimise stocking strategies through pilot-scale releases

� Use empirical data from pilot releases to control enhancement impacts9) Identify economic and policy guidelines

� Assess value of enhancement in terms of costs and benefits10) Use adaptive management

� Adopt a continuing assessment process that allows improvement over time

� Allow integration of new ideas and strategies into the management process

This approach was designed to maximize the chance of successful stock enhancement and reduce

the probability that failures are repeated.

Each step includes a brief summary of the key points proposed by Blankenship & Leber (1995).

MARINE FINFISH STOCK ENHANCEMENT IN AUSTRALIAN ESTUARIES 301


experiences of successful and failed marine stock enhancement projects else-where, the design of sustainable stocking programs may be possible.Only nine of the 300 commercially fished species in Australian waters may

sustain higher catches with natural recruitment (Kailola et al., 1992). Thereforerecent developments in spawning technology and extensive aquaculture techni-ques for the large-scale rearing of over 20 Australian marine finfish species(Battaglene & Fielder, 1997) may provide for future growth. Australia is takinga cautious approach to stock enhancement before investing in infrastructure orlarge-scale enhancement projects. Increases of recreational fishing effort inAustralia (up to 7�5% per year, Gwynne, 1994), is putting additional pressureon fish stocks, and stocking of marine finfish into estuaries is progressivelygaining favour as a management option (Huggan, 2001).This review examines the status and future prospects of marine finfish stock

enhancement in Australia, in the context of the 10-step responsible approachdescribed by Blankenship & Leber (1995). It demonstrates the advantages thatintermittently open-closed estuarine lagoons provide as experimental units toassess stocking, the relatively greater benefit for stocking to enhance recreationalfisheries over commercial, the selection of suitable species based on growth, andthe pragmatic application of these ten guiding principles.

PRAGMATIC APPLICATION OF THE RESPONSIBLE APPROACH

The Blankenship & Leber (1995) responsible approach to marine stockenhancement (Table I) is designed to reduce the chance of a past failure beingrepeated. One economic failure is the stocking of pink salmon Oncorhynchusgorbuscha (Walbaum) in Prince William Sound, due to declines in survival andpoor market prices (Hilborn, 1998). The stocking of cod Gadus morhua(Linnaeus) in Masfjorden was a biological failure, where competition for foodresources led to low survival of hatchery-reared fish (Svasand et al., 2000). Theresponsible approach embodies a framework with which aquaculture technologycan be used to expand and enhance natural resources, however there are fewexamples where all principles have been covered (Leber & Arce, 1996; Ziemann,2004). Many programs may be temporally or financially constrained, and theseprograms need to identify and address the most pressing points within the 10principles.

PRIORITISE AND SELECT TARGET SPECIES FORENHANCEMENT

Selection of species for stock enhancement could be based on the availabilityof aquaculture technology or the immediate needs of a lobby group or stake-holder in the community. To remove this bias a framework involving input fromthe community, and the ranking of candidate species according to some expli-citly defined criteria should be employed (Blankenship & Leber, 1995). Somesuggested criteria are shown in Fig. 1, however ranking of these primarilydepends on the goals, duration and level of funding available for the stockingprogram. The first step is to determine which species are present or occurredhistorically in the area to be stocked. There should be evidence of a decrease in



catch due to recruitment limitation from either removal of spawners or physicalbarriers to recruitment, or evidence of additional carrying capacity (from habitatrestoration). Munro & Bell (1997) identify some important biological character-istics of species to be stocked, including fast growth and narrow habitat prefer-ences. Fast growth is important to ensure benefit from stocking is obtained in 2–4 years. Habitat preferences will indicate how many fish to release, and where torelease and harvest the fish. Species that are highly migratory, oceanic or non-estuarine residents cannot be effectively stocked, as high rates of dispersal, ordilution confound effective harvest. Ideal candidates for stocking are estuarineresidents, at least until they enter the fishery and can be harvested. From afinancial perspective, the existence of aquaculture technology for the species, andthe demonstrated success of stocking particular species elsewhere can minimizethe costs of stocking, whilst enhancing recreational fisheries generally has abetter cost-benefit ratio and greater funding potential.Estuarine resident species for which culture technology is available or is under

investigation in Australia are listed in Table II, with some of the above criteriaapplied for these species. These species are ranked according to number caughtin the recreational fishery in 2001 (Henry & Lyle, 2003), and market value isincluded as an indication of the value of the species to the commercial fishery(but not to the recreational fishery). The growth coefficient (K), asymptotic size(L1), and natural mortality (M) to K ratios are provided where possible. M/Kratios usually lie between 1�12 and 2�5 for all fish species (Ofori-Danson et al.,2001), and lower ratios indicate lower natural mortality and higher growth rate.

Species Selection

• Estuarine resident

•Fast growth to minimum legal length

• Aquaculture technology

• Recruitment limited

• Success elsewhere

• Evidence fordecline in catch

• Habitat restoration

Biological

Other Financial

• Popular recreational

• Impacted/urban estuaries

FIG. 1. Suggested criteria for selecting species for stock enhancement. Criteria can be broadly divided into

three categories: financial considerations, biological considerations and other considerations invol-

ving the motivation for stocking a particular species.



TABLEII.Summary

ofestuarinefinfish

speciesforwhichaquaculture

technologyexists,orisunder

investigationin

Australia

Scientificname

Family

Commonname

Population

structure

Legalsize

(cm)

Value

K(M

/Kratio)

L1

Ranked

recreational

catch

Comments

Salm

osalar

Salm

onidae

Atlanticsalm

on

Known

–3

0�1

(11)

39

8Non-native

Oncorhynchus

mykiss

Salm

onidae

Ocean/rainbow

troutInconclusive

38*

20�5

(2�8)

58

8Non-native

Rhombosolea

tapirina

Pleuronectidae

Greenback

flounder

Unknown

23**

1–

45#

14

Mainly

commerciallyfished

Ammotretis

rostratus

Pleuronectidae

Long-snoutflounder

Unknown

23**

1–

25#

14

Mainly

commerciallyfished

Latrislineata

Latridae

Striped

trumpeter

Unknown

25*

3–

120#

10

Highly

desired

but

difficultto

produce

Cheilodactylus

spectabilis

Cheilodactylidae

Banded

morw

ong

Unknown

–1

–100#

13

Growsto

largesize,

butlittle

inform

ation

knownaboutthespecies

Acanthopagrus

butcheri

Sparidae

Black

bream

Under

investigation

25

20�19

41

3Verypopularangling

species,more

common

tothewestcoast

Acanthopagrus

australis

Sparidae

Yellowfinbream

Inconclusive

25

20�51

30

3Verypopularangling

fish,usuallyhasstrong

recruitmenton

east

coast

Macquaria

novemaculeata

Percichthyidae

Australianbass

Known

35

20�22

(1�14

)37

12

Commonly

stocked

in

freshwatersystem

s

Pagrusauratus

Sparidae

Snapper

Known

30

30�29

108

6Swim

soutofestuaries

Argyrosomas

japonicus

Sciaenidae

Mulloway

Under

investigation

45

3–

172

11

Fast

growingestuarine

resident,successfultrials

Sillagociliata

Sillaginidae

Sandwhiting

Inconclusive

27

20�39

39

1Verypopularangling

fish,usuallyhasstrong

recruitment,

successfultrials

Sillagomaculata

Sillaginidae

Trumpeter

whiting

Inconclusive

27

1–

30

1Verystrong

naturalrecruitment



Acanthopagrus

berda

Sparidae

Pikey

bream

Unknown

23*

20�38

(0�81

)38

3Largeinshore

species,

limited

tonorthernAust.

Latescalcarifer

Centropomidae

Barramundi

Known

58*

21�82

178

15

Iconic

statuswith

recreationalfishers.

Verypopularanglingfish,

successfulstockings,

limited

tonorthernAust.

Lutjanusjohnii

Lutjanidae

Golden

snapper

Unknown

35*

20�38

96

9Lim

ited

timein

estuary

Lutjanus

argentimaculatus

Lutjanidae

Mangrovejack

Unknown

35*

20�19

(1�31

)105

9Popularanglingfish,

butslow

growingand

difficultto

produce

Mugilcephalus

Mugilidae

Mullet

Unknown

30

10�40

(0�83

)50

5Predominately

commerciallytargeted

Anguilla

australis

Anguillidae

Shortfinned

eel

Known

30

1–

––

Mainly

freshwater

Sillaginodes

punctata

Sillaginidae

KingGeorge

whiting

Known

27

21�17

53

4Highly

popularboth

commerciallyand

recreationally

Platycephalus

fuscus

Platycephalidae

Duskyflathead

Unknown

36

10�22

85

2Verypopularangling

fish,estuarineresident,

successfultrials

Caranxspp.

Carangidae

Trevally

Unknown

–1

0�30

45

7Highly

migratory,

driftsin

andoutof

estuaries

Lethrinusspp.

Lethrinidae

Emperors

Under

investigation

38

20�50

(0�58

)43

13

Occasionallyin

estuaries,

more

targeted

to

rockyreefs

Thislisthasbeenupdatedfrom

anearlierlistofspeciesin

Battaglene&

Fielder

(1997).Thestatusofthepopulationstructure

isgiven

foreach

species.Although

technologyisavailableto

culture

thesefish,manyofthesespecieslisted

are

lackingin

crucialinform

ationonpopulationstructure.Legalsizesare

forNew

South

Wales,Queensland(*)orVictoria(**).Valuerepresents

ranges

from

$AU1–5kg�1(1),$AU6–10kg�1(2)or$AU11–15kg�1(3)from

Sydney

orMelbourne

FishMarketsin

2003.Allnaturalmortality

(M)andgrowth

(K)coefficients,andmaxim

um

length

(L1)values

are

taken

from

Froese&

Pauly

(2003),exceptfor

(#)whichare

maxim

um

reco

rded

lengthsfrom

Kuiter

(2002).M/K

values

are

provided

forspeciesforwhichM

wasavailable

throughFroese&

Pauly

(2003).

M/K

values

are

aratioofnaturalmortality

(M)to

growth

(K)coefficients

(after

Munro

&Bell,1997).A

low

M/K

valueandalargeL1

are

goodbiological

attributesforacandidate

stock

enhancementspecies.Ranked

recreationalcatchrepresents

arankofthelisted

speciesbytotalnumberscaughtduringthe12

monthsto

2001(H

enry

&Lyle,2003),thisinform

ationisnotavailableforallspecies.Those

speciesreceivingequalrankhavehadtheirdata

grouped

inHenry

&

Lyle

(2003).Note

thatalthoughrelevant,geographicalrangeorstock

statusare

notconsidered

here.



Low M/K ratios and high asymptotic size are additional attributes that may beused to define ideal candidate species (Munro & Bell, 1997).Successful enhancement has been achieved elsewhere for several identical or

related species to those in Table II. For example, striped mulletM. cephalus havebeen successfully stocked in Hawaii (Leber, 1994). Small-scale releases of cul-tured fish (20 000–81 000 individuals) into nursery habitats in Kaneohe Bay in1991 led to an increase in abundance by up to 33% at some release sites (Leberet al., 1995). By optimizing release strategies survival of released M. cephalusincreased over 400% (Blankenship & Leber, 1995) and provided a 20% con-tribution to catch in recreational fisheries in Hawaii (based on estimates fromcoded-wire-tagged individuals, Blankenship & Leber, 1995; Leber et al., 1995).Australian M. cephalus (sea mullet) has an important commercial fishery forboth local and export markets, with a national catch of 5100 t for 2003 worthover $AU12 million (ABARE, 2004), and there is evidence for a decline in thestock in NSW waters at present (Smith & Deguara, 2002). The relatively loweconomic value of M. cephalus (Table II) does not take into account the exportof roe and the value of this species to many rural communities in Australia. Inaddition, M. cephalus can be cultured at low cost using wastewater from prawnaquaculture (Palmer et al., 2002).The Texas Parks and Wildlife Department (TPWD) implemented a program

that aimed to significantly (P ¼ 0�10) increase landings of red drum S. ocella-tus by sport-boat anglers over historic catch rates (Matlock, 1990), through acombination of stocking and bag/size limits (McEachron & Daniels, 1995;McEachron et al., 1995). Currently, the TPWD releases between 20 and 30million red drum fingerlings (25 mm TL) annually into Texas bays (Silva &Bumguardner, 1998), and post-1990 this has contributed to an increase of upto 30% in recreational catch rates (McEachron & Daniels, 1995; McEachronet al., 1998). Red drum have similar growth rates and life history to the jewfishor mulloway Argyrosomus japonicus (Temminck & Schlegel), which are ende-mic to the waters of southern Australia (Kailola et al., 1992). Both speciesexhibit growth up to 1 mm d�1 (Silva & Bumguardner, 1998; Fielder et al.,1999), and remain in estuaries until they can be harvested (Kailola et al., 1992;McEachron et al., 1995). Catches of this species in Australia have been steadilydeclining over the past 20 years from 250 t in 1980/81 to 64 t in 1999/00(ABARE, 2001).Several other Australian species may prove viable candidates for stock

enhancement (Fig. 1 and Table II). Sillago ciliata (Cuvier), Platycephalus fuscus(Cuvier), and Acanthopagrus butcheri (Munro) and A. australis (Gunther) areideal enhancement candidates because they are common residents of estuaries,and are heavily targeted recreational species, thus are more likely to produce ahigher return on investment in stocking than for commercial species or speciesless targeted. Unfortunately these species take >5 years to reach legal size, andare not demonstrably recruitment limited. Lethrinus sp. (Bloch & Schneider) hasa relatively low M/K ratio, but they migrate in and out of estuaries and are notas common in the recreational catch. Species such as Lates calcarifer (Bloch) andA. japonicus are valuable and highly sought after sportfish, and M. cephalus isimportant to both recreational and commercial fisheries (Table II). These threelatter species are fast growing estuarine residents for the majority of their lives,



and L. calcarifer and A. japonicus have been successfully stocked previously inAustralia (Table III), and M. cephalus in Hawaii (Leber & Arce, 1996).

DEVELOP A SPECIES MANAGEMENT PLAN

The development of individual species management plans will evaluate theuncertainties, assumptions and expectations about the performance of theenhancement program (Blankenship & Leber, 1995). Australian fisheriesresources are generally managed by fishery, rather than at the species level, butreviewing the biology of the target species in the context of the overall fisherymanagement plan will enable enhancement efforts to be targeted toward areaswhere success will be maximized. For example, a closure in the NSW EstuaryPrawn Trawl fishery for part of the year may provide the opportunity to stockspecies that use the trawling grounds as a nursery area. Although this approachdeviates from the responsible approach (which advocates individual speciesmanagement plans), management by fishery allows the consideration of theimpacts of stock enhancement on all aspects of the fishery (ecosystem basedmanagement). Stock enhancement can also help address the objectives of thefishery management strategy, such as performance targets. Management plansusing stock enhancement should be designed so that stocked fry or fingerlingsare protected by closed seasons surrounding release times, or stocking intonursery areas that are closed to fishing, and/or protection from destructivefishing methods.In March 2001 a saltwater recreational fishing license was introduced in NSW,

generating funds for a recreational fishing trust to improve recreational fishingin NSW. A large proportion of the initial funds generated by this license havebeen used to buy back commercial fishing licenses, and create 30 estuarinerecreational fishing havens (RFHs), which are estuaries closed to commercialfishing (NSWF, 2002). The advent of recreational fishing havens in Australiaprovides an opportunity to stock into areas that are not susceptible to commer-cial fishing with destructive gear types like beam or otter trawling (Gibbs et al.,1980), cast-netting and beach-hauling (Otway & Macbeth, 1999). In addition,stocking projects may be completed alongside restoration of habitat that hasbeen damaged by commercial fishing or urbanization.Management plans involving stock enhancement may also include habitat

restoration to assist stocking efforts (Blankenship & Leber, 1995). Habitatrestoration is often advocated in place of stocking, however in urbanized areasit may never occur to a level where the fishery is actually enhanced (Elliott &Hemingway, 2002). In Australia, there are several discouraging examples ofhabitat restoration in urbanized areas. One such example is the transplantationof Zostera capricornia seagrass beds to compensate for the environmental effectsof construction of the third Sydney airport runway in Botany Bay. Naturalrecolonization or the large-scale transplanting of seagrass failed to produceany sustained increase in seagrass biomass or shoot density due to high waveenergy and water movement as a result of the runway (Gibbs, 2001). Americanshad Alosa sapidissima (Wilson) restoration in the Susquehanna River is apromising example of habitat restoration being used in conjunction with stock-ing of fingerlings to rebuild fish stocks. American shad populations declined



TABLEIII.

Pilotmarinefinfish

stockingprojectsundertaken

inAustraliato

date,and

adherence

totheten

principlesofmarinestock

enhancement

Species

State

Duration

Fishreleased

size

(mm)

Number

Marking

method

Number

ofprinciples

addressed

Sillagociliata

Sth.Qld.

3years

22–101

346250

SPA

1,5,7&

9Butcher

etal.(2003)

Platycephalus

fuscus

Sth.Qld.

3years

29–58

86000

SPA

1,5,7&

9Butcher

etal.(2003)

Argyrosomus

japonicus

Nth.NSW

3years

40–106

75000

OTC

5,7&

8Fielder

etal.(1999)

Sth.&

Nth.

NSW

Ongoing

50–100

127000

OTC

ALC

5,7,8&

9Tayloret

al.(unpubl.data)

Acanthopagrus

butcheri

WA

3years

<203

Severalthousand

T-bar

7Lenantonet

al.(1999)

Latescalcarifer

Nth.Qld

9years

30–300

108000

CWT

5,7,8&

9Rim

mer

&Russell(1998)

Russellet

al.(2004)

Sth.Qld.

2years

10

600000

Notmarked

Nil

Palm

er(1995)

Amaxim

um

offouroftheten-principlesofBlankenship

&Leber

(1995)wereaddressed

orpartiallyaddressed

byanAustralianstudy(numberscorrespondto

principlesin

Table

I).Sillagociliata

andPlatycephalusfuscusstockingwerepartofthesameproject.NomonitoringwascarriedoutfortheSouth

Queensland

Latescalcariferstockings.

SPA,scale

patternanalysis;OTC,oxytetracyclinehydrochloride;

CWT,coded

wiretags;ALC,alizarincomplexone.

Sth.Qld.,South

Queensland;Nth.Qld.,NorthQueensland;Sth.NSW,South

New

South

Wales;

Nth.NSW,NorthNew

South

Wales;

WA,Western

Australia.



dramatically after the construction of four hydroelectric dams along the courseof the river (Hendricks, 2003; St. Pierre, 2003). Between 1985 and 2000, fishladders and fish lifts have been constructed at each of the dams to re-openapproximately 750 km of spawning habitat, over 166 million American shadlarvae and fingerlings have been released into the river, and over 266 000individuals have been transported upstream past the power stations (St. Pierre,2003). Over this time period American shad counts in the Conowingo Dam(16 km upriver from Chesapeake Bay) increased from 300 year�1 to over 250000 year�1 (St. Pierre, 2003).Stock enhancement may also be used to address the objectives of aquaculture

management plans. For example, the culture of fingerlings for release (e.g.M. cephalus) using waste nutrients in Australian prawn farm settlementponds would have a two-fold benefit of minimising the waste released intothe environment and producing fingerlings at a relatively low cost (Palmeret al., 2002).

DEFINE QUANTITATIVE MEASURES OF SUCCESS

Carrying capacity is a measure of the biomass of a given population thatcan be supported, in terms of available food and habitat (including availablerefugia) in the ecosystem (Cooney & Brodeur, 1998). It varies among speciesdepending on the behaviour and bioenergetic efficiency of the fish. Carryingcapacity may be under-exploited if the stock is recruitment limited (Svasandet al., 2000), but exceeding the carrying capacity of an ecosystem can lead tothe displacement of other individuals that share the resources, or a shift inthe ecosystem (Molony et al., 2003). Habitat restoration or creation may beused to increase carrying capacity to historic levels, and enhance the capacityof the ecosystem to support additional recruits or mitigate anthropogeniceffects. Defining enhancement measures of success and objectives concern thedegree to which a system can support additional recruits in terms of habitatand food, which is largely on the carrying capacity of a system. This notionalconcept can be pragmatically assessed by the growth and survival of releasedfish, a result of density dependent processes of predation, growth, cannibal-ism and competition (Myers & Cadigan, 1993; Kellison et al., 2002), orthrough linking an estimation of available resources with growth in the targetspecies. Results can often be confounded by migration in and out of thesystem, and changes to the system caused by stocked fish (Rutledge, 1989).In addition, wild or competitor species may be displaced if density is toohigh. Munro & Bell (1997) propose that knowledge of the carrying capacityof the target habitat is required to make effective use of juveniles and preventoverstocking, as shown by the failed experience with cod in Western Norway(Moksness, 2004) and salmon in the Pacific Northwest (Cooney & Brodeur,1998). Enhancement objectives and measures of success should therefore bedefined by the modelled carrying capacity in terms of available food andhabitat resources, or by growth and survival targets for released fish, ratherthan historical catch rates.Several ecological risks associated with marine stocking are reviewed by

Molony et al. (2003), and grouped into three broad areas. Species-specific risks



include genetic and disease risks, increased intra-species competition, shifts inprey consumption and the resulting potential displacement of wild conspecifics(Molony et al., 2003). Interspecific risks include increased interspecific competi-tion and potential displacement of competing species (Molony et al., 2003). On alarger scale, ecosystem-wide risks include shifts in prey abundance, shifts in thedistribution or biomasses of other species and resulting extinctions, and physicalenvironmental damage from the actual stocking (Molony et al., 2003). With theexception of genetic and disease risks (described in later sections) and physicalenvironmental damage, most of the risks described above can be alleviated by asuitable assessment of the carrying capacity for the target species in the targetsystem and small-scale pilot experiments to evaluate in situ the effects of stockingon conspecifics, competitors and prey.Carrying capacity for higher trophic levels is often estimated from primary

production in a system. In marine systems production can be regulated bynutrient upwelling (Aksnes et al., 1989), and from terrestrial sources (Luoet al., 2001). Australian oceanic waters are characteristically nutrientdepleted, as there are no northward moving currents to transport nutrientrich sub-Antarctic waters to the continental shelf. In addition, there is limitedterrestrial runoff to estuaries in southern Australia, and the majority ofcoastal soils around Australia are deficient in phosphates (Rochford, 1979).The primary nutrient deficiency may constrain the capacity of some estuariesto support additional recruits (Kearney & Andrew, 1995). Australia also hasa large number of eutrophic estuaries resulting from nutrient runoff fromagricultural/urban land usage, and poor tidal flushing due to constrictedopenings. In these situations, constricted openings can also limit recruitmentto the estuary from ocean spawners. Production in estuarine systems can beestimated by water quality models, such as the Simple Estuarine ResponseModel (SERM, Baird et al., 2003). Primary and secondary production esti-mates from these models can be linked through the trophic cascade todetermine both ideal stocking density, and potential production of thestocked species through bioenergetic models for the target species (e.g.Pauly, 1986; Giske et al., 1991; Salvanes et al., 1992; Luo et al., 2001).This approach can provide a baseline for setting quantitative measures ofsuccess based on the productive capacity of the ecosystem. Pilot-scale releasescan be used to refine this baseline to account for actual density-dependentprocesses in the field. Pilot-scale release-recapture experiments can also beused to test assumptions about the carrying capacity of a target ecosystemand enhancement tactics (Leber et al., 1995), linking stocking density andsurvival with estimated carrying capacity. These programs can be expensive,and success may be hindered when stocking open systems as fish have theopportunity to emigrate from the stocking site. The selection of a suitablesite to test stocking tactics should be primarily based on the inability for fishto move large distances away from the release site, and the selection of a sitewithin the natural habitat range for the species. This pilot-scale releaserequirement is minimized through a modelling approach to theoreticallyassess ideal stocking density. If stocking occurs close to the level the systemcan sustain, high growth and survival should follow and the need for a largeseries of pilot-scale releases may be reduced.



USE GENETIC RESOURCE MANAGEMENT

Stock enhancement has a range of potential effects on the genetics of wildpopulations of marine finfish. The Blankenship & Leber (1995) approachinvolves five key points to minimize deleterious genetic effects (Table I).All stock enhancement programs pose some risk to the effective population

size (Tringali & Bert, 1998). The higher fecundity of marine species may leadto a potentially higher susceptibility to genetic problems than for less fecundsalmonids and freshwater species as there is a greater opportunity for fortuitoussurvival of offspring from very few matings (Utter, 1998). Marine/estuarine spe-cies are typically more genetically homogenous than freshwater/catadromousspecies and often show relatively little stock separation (Blankenship & Leber,1995). For example, the common estuarine species in southern Australia A.japonicus (Black & Dixon, 1992) and A. butcheri (Farrington et al., 2000) exhibitpanmictic populations, while northern Australian catadromous species L. calcar-ifer (Shaklee & Salini, 1985; Salini & Shaklee, 1988) and Polydactylus sheridani(Gunther) (Garrett, 1997) exhibit geographic genetic differentiation. Stock-specificmanagement practices should be applied when species display geographic differ-entiation (Shaklee et al., 1993) to prevent deterioration of localized genetic char-acteristics, and stocking programs involving such species need to closely monitorthe effective size of the hatchery broodstock. To minimize potential erosion oflocalized genetic characteristics as a result of stocking, L. calcarifer fingerlingsstocked in northern Queensland were produced using only broodstock that weretaken from the population targeted for enhancement (M. Rimmer, pers. comm.).The first four points for responsible genetic resource management (Table I) may

be applied in the planning stage of the enhancement project, however geneticallymonitoring and controlling hatchery and wild populations is both costly anddifficult to implement. Aquaculture facilities in Australia are limited in size andnumber, and maintenance of sufficient numbers of effective breeders as brood-stock to preserve genetic diversity may prove too expensive for many operators. Itis accepted that between 100 and 200 breeders with an equal sex ratio is sufficientto maintain most genetic variation in hatchery populations (Bartley et al., 1995;Carvalho & Cross, 1998), and the successful application of this is observed in theculture of white seabass Atractoscion nobilis (Ayres) in California (Bartley et al.,1995) and of red drum S. ocellatus in Texas (King et al., 1995). Where themaintenance of large numbers is not feasible, the strip spawning of wild indivi-duals from the population to be stocked may provide a viable alternative, depend-ing on the ease of capture and response of the species to handling. This methodhas been used successfully for red drum (Colura et al., 1990) and the Black Seabass Centropristis striata (Linnaeus) (Chappell et al., 2001), and with severalAustralian species including snapper Pagrus auratus auratus (Tabata &Taniguchi) (Cleary et al., 2002), black bream A. butcheri (Haddy & Pankhurst,2000) and striped trumpeter Latris lineata (Forster) (Ruwald et al., 1991).

USE DISEASE AND HEALTH MANAGEMENT

Stocking of diseased fish into the wild could contaminate wild stocks or resultin low survival of released fish (Johnson & Jensen, 1986; Bakke et al., 1990).



High nutrient and organic loads, and low flushing of wastes in culture situationshave the potential to lead to bacterial, viral and/or protozoan proliferation.Handling stress, exposure to unnatural conditions and high rearing densitiesincrease the vulnerability of fish to pathogens. In addition, the use of antibioticssuch as oxytetracycline in hatcheries may increase antibiotic resistance in bac-teria. Several diseases are prevalent in the aquaculture of Australian marinefinfish including pilchard herpesvirus in Sardinops sagax neopilchardis, flounderherpesvirus in Rhombolsolea tapirina (Gunther) and barramundi nodavirus in L.calcarifer (Munday & Owens, 1998).The disease and health guidelines implemented in Florida in association with

red drum stockings require that all groups of fish pass certified bacterial, viraland parasite inspections before release (Blankenship & Leber, 1995), whereinfection levels in healthy wild populations are used to determine maximumacceptable levels in fish for release. The health assessment index (HAI) used byPalmer et al. (2000a) to provide a health profile for fish destined for release in theMaroochy Estuary stocking program in Queensland, accounted for many ofthese concerns, and could provide measures of fingerling quality for covariateanalysis of survival from different batches released. Sub-samples of each batch offingerlings were examined macroscopically and rated with a HAI score, scoring adegree of normality (0–3) of fins, eyes, gills, liver, spleen, kidney, gall and thepresence of mesenteric fat, whitespot and trematodes (Palmer et al., 2000a).Numerical values for all parameters are summed for each fish in a sample andaveraged for the population, the best score being 0 and the worst score being 30.The use of HAI should be supplemented where necessary with veterinary inspec-tions to detect such things as vacuoles in the central nervous system of larvalfish, which are evidence of a nodavirus infection (Munday et al., 1992). Inaddition, all activities involving the use of vertebrate animals should haverelevant animal care and ethics approval, to ensure ethical and humane handlingand euthanasia of infected or diseased animals.

IDENTIFY RELEASED HATCHERY FISH AND ASSESSSTOCKING EFFECTS

Recognizing stocked fish is essential to assess the effectiveness of enhance-ment, as natural fluctuations in fish stocks can mask successes or failures(Blankenship & Leber, 1995). For the performance of stocked and wild fish tobe comparable, tags must not affect behaviour, biological functions or survival(Buckley & Blankenship, 1990). Three cheap, simple and effective methods oftagging used for marine species in Australia are coded-wire tags, scale patternanalysis and chemical marking of otoliths.Coded-wire tags (CWT) implanted in snout cartilage (Jefferts et al., 1963), the

gut-cavity or various muscles (Ingram, 1989; Russell et al., 1991) using auto-matic injectors, are detected by portable or stationary X-ray or electronic metaldetectors. To read the tag’s binary code it must be removed from the fish (Ebel,1974; Wooley et al., 1990). Coded-wire tags were successfully used in the evalua-tion of coastal enhancement efforts of barramundi, L. calcarifer, in NorthQueensland (Russell et al., 1991; Russell & Hales, 1992; Rimmer & Russell,1998), however set-up costs were relatively high. This project allowed insertion of



up to 270 tags per hour, 93% retention after two months, with no decrease in tagretention after 394 days at liberty (Russell & Hales, 1992).Patterns on scales or otoliths have many applications in species and stock

discrimination (Anas & Murai, 1969; Major et al., 1972; Ross & Pickard, 1990;Barlow & Gregg, 1991; Willett, 1993, 1996; Silva & Bumguardner, 1998). Severalstudies have shown that intercirculi distances on scales are dependent on growthrates, which in turn can be manipulated in hatcheries through environmentalfactors that influence metabolic processes (feeding rates, water temperature,stress, Pepperell, 1989; Volk et al., 1990). Sudden drops in water temperaturehave been shown to produce optically dense zones, and unique patterns havebeen induced with regularly repeated thermal cycles and feeding regimes (Volket al., 1990), however natural variations in growth can create interpretationdifficulties so the induced marks must be distinctive. Scale pattern analysis wasapplied to the sand whiting S. cilliata and dusky flathead P. fuscus during thepilot stocking program in Queensland in 1995. This technique allowed 75–89%correct classification of fish as stocked or wild (Palmer et al., 2000b; Butcheret al., 2003).Captive fish populations can be marked en-masse by immersion in chemicals

that produce fluorescent marks on otoliths, including tetracycline, calcein, ali-zarin compounds, and strontium (Brothers, 1990). Immersion in fluorescentchemicals can also produce marks in fin-spines (Fig. 2), which are ideal forsampling fisheries as marks can be detected without mutilation of the fish(Taylor et al., 2005). Oxytetracycline (OTC) is an antibiotic regularly used in

OE A

FIG. 2. Transverse anal fin spine section from a mulloway (Argyrosomus japonicus) 120 days after release

(100 mm TL) showing an alizarin complexone mark when the fingerling was 100 mm (OE ¼ outer

edge of fin spine, A ¼ ALC mark). Chemical marks such as alizarin complexone that are incorpo-

rated and maintained in the fin spine allow non-invasive detection of stocked fish. Scale bar

represents 100 mm.



hatchery practice, and has been successfully used to mark cod G. morhua inenhancement experiments in Norway (Svasand, 1993), and hatchery-producedlarval and juvenile striped bass Morone saxatilis (Walbaum) (Secor et al., 1991)with minimal mortality. Dilution of seawater is necessary since OTC hydro-chloride chelates with Mg2þ and Ca2þ ions which reduces the amount of chemi-cal available for uptake (Hettler, 1984; Lunestad & Goksøyr, 1990). Tetracylinemarks can persist for up to four years (Drawbridge et al., 1993), however markretention in calcified structures exposed to sunlight (e.g. scales) is minimal sincetetracycline degrades in UV light (Blom et al., 1994). Marking of Australianspecies by immersion in OTC has met with mixed success. Immersion of sandwhiting S. ciliata and dusky flathead P. fuscus in OTC generally resulted in lowmark quality and high mortality (Palmer et al., 2000b; Butcher et al., 2003), whileOTC immersion of mulloway A. japonicus in diluted seawater resulted in highmark quality and negligible mortality and retention of marks in stocked fish 420days after marking (Taylor et al., 2005).Alizarin compounds have been used to mark otoliths in concentrations from 3

to 1000 mg L�1. (Tsukamoto et al., 1989; Blom et al., 1994). Generally, markingusing alizarin complexone has no detectable effect on growth and mortality(Tsukamoto, 1988; Beckman & Schulz, 1996; Sanchez-Lamadrid, 2001), andmarks have been retained for over two years (Tsukamoto et al., 1989), but it iscomparatively expensive (>$AU12 g�1). Alizarin red S is a cheap alternative toalizarin complexone (�$AU0.50 g�1), but has been shown to cause mortality ineggs and larvae at concentrations 100–400 mg L�1 (Blom et al., 1994). Alizarincomplexone was also successfully used to batch mark A. japonicus, and markswere retained in stocked fish up to 120 days after marking (Fig. 3, Taylor et al.,2005). Double immersions also provide the opportunity to identify individualsfrom different release cohorts or treatments.

Prey species Stocked species Competitor species

Cha

nge

in c

atch

rat

e

• Displacement due tostocking may be occurring

• Recruitment failure

• Adverse conditions

• High prey:predator ratio, stocking density may be increased

• Stocking may have failed

• Stocking level too high

• Recruitment failure

• Adverse conditions

• Stocking level adequate at present

• Stocking level ineffectual, consider changing stocking strategy

• Stocking level adequate at present

•Exceptional recruitment/conditions, potentially stock at a greater density

• Stocking successful, evaluate change in prey/predator abundance

• Exceptional recruitment/conditions, potentially stock at a greater density

–ve

+ve

0

FIG. 3. Hypothetical system development matrix for stock enhancement of a finfish species. Performance

of the stocking activity is evaluated in terms of the abundances of the three groupings shown (prey

species, stocked species and competitor species), and possible strategies for future stocking activities

adjusted in response (matrix structure adapted from Thom, 1997).



Some enhancement projects have examined genetic marking as a means toidentify stocked fish. Lower levels of genetic divergence in many marine fishspecies (Baduge & Gunnar, 2001) make cultured populations attractive candi-dates for intentional genetic marking, however selective breeding for specificgenotypes may affect performance traits in the cultured population, thus in thelong term affecting the performance of augmented populations (Utter & Seeb,1990). A relatively small number of founder individuals with the desired geno-type can cause a narrow genetic base in fish cultured for release, as was found forG. morhua in Western Norway (Utter & Seeb, 1990; Jørstad, 1994). Markers alsoneed to be selectively neutral, and usable markers may be difficult to obtain. Thedangers, difficulty, and cost involved in this approach do not support the use ofintentional genetic marking.

USE AN EMPIRICAL PROCESS TO DEFINE OPTIMUMRELEASE STRATEGIES

It is logistically difficult to quantify survival of stocked fish in coastal envir-onments (Leber et al., 1996), but this information is central to the successfulimplementation and evaluation of a stock enhancement program (Blankenship &Leber, 1995). The relative survival of fish can have significant implications forthe size at release, the quantities of fish that are stocked, and the season, timeand habitat suitabilities. For example, several red drum releases in Texas(McEachron et al., 1998), Florida (Willis et al., 1995) and South Carolina(Smith et al., 1997) have shown variable survival in response to salinity andtemperature, the effects of which are amplified with decreasing size-at-release.Survival can be maximized by timing releases so that size modes betweenhatchery and wild stocks were similar (Leber et al., 1997), and stocking fish ata density that ecosystem production can support.Release strategies should be refined to maximize survival through pilot-scale

releases (Blankenship & Leber, 1995). If monitored effectively, small-scalerelease experiments can point to operational procedures that optimize survivaland cost-benefit, and ultimately minimize any adverse ecological effects. This isevident in the successful stocking of striped mullet M. cephalus in Hawaii (Leber& Arce, 1996) and red drum S. ocellatus in Texas (McEachron et al., 1998) wherepilot-scale experiments were used to refine techniques. All marine releases con-ducted in Australia to date (Table III) have been pilot studies with broad aimsthat mainly concern evaluating whether stocked fish can survive and recruit tocommercial or recreational catches. The next step in Australian enhancementstudies is to resolve optimal habitat, season and size of release in a closed system,un-confounded by emigration. There are few completely closed marine systems,however 92% of estuaries in New South Wales (NSW) have restricted entrances(Griffiths, 2001a), and 54% of south-east Australian estuaries are classified ashaving intermittently opened entrances (ICOLLs, Roy et al., 2001). An experi-mental approach was used by Kellison et al. (2003) to refine release strategiesand evaluate pilot enhancement for the summer flounder Paralichthys dentatus(Linnaeus), however this was in an open river system. As ICOLLs are not alwaysopen to the sea, they can serve as temporary experimental units to both assesscarrying capacity and define optimum release strategies in the absence of



emigration. The opportunity also exists to genetically evaluate whether naturalpopulations are augmented or replaced by stocking activities in a semi-closedsystem (Hilborn, 1999).ICOLLs are often eutrophic (Roy et al., 2001), with large abundances of

forage fish species (e.g. Atherinidae, Clupeidae and Gobiidae) and Crustacea(Robinson et al., 1982; Gray et al., 2000). The restricted or closed entrancesproduce a physical barrier to recruitment that can result in recruitment limita-tion of species that spawn at sea or at the mouths of estuaries (Griffiths, 2001b).Recruitment limitation in these ICOLLs from both physical barriers andremoval of spawners may justify enhancement of some species. Furthermore,40% of recreational fishing havens are classified as having restricted entrances orbeing ICOLLs, and this has several implications for stock enhancement. In theabsence of commercial trawling and beach hauling in estuaries, additionalprawns and other forage resources may be available, and juvenile fish are lesslikely to become by-catch of commercial fishing gear. Experimental manipula-tion of size/cost at release and stocking density could be achieved in ICOLLs,although these systems can unpredictably open to the sea with heavy rainfall.

IDENTIFY ECONOMIC AND POLICY GUIDELINES

The goals of a stocking program should also be evaluated in terms of programcost against perceived or calculated benefit. Economic models not only weigh thecosts against the benefits of enhancement programs, but may also aid policymakers, and create additional funding opportunities through reprioritization,legislation, and user fees (Blankenship & Leber, 1995). Cost-benefit analysis(Rutledge, 1989) is a pragmatic way of deriving economic objectives and pre-dicting the value of enhancement (Table IV), however the aesthetic value ofcatching a fish and associated dollar value of a fish to a recreational fishermay be over-estimated. Possible costs and benefits of stocking, and examplesof some cost-benefit evaluations are shown in Table IV. Motivational character-istics change for different angler groups, preventing a general formula forestimating the aesthetic value of fishing (Fedler & Ditton, 1994). Evaluatingenhancement of stocks that are predominantly commercially fished may result inmuch higher cost/benefit ratios (e.g. Hilborn, 1998) as there is little aestheticvalue, and the dollar value is usually limited to the market price of the species.More detailed bioeconomic models are available for cost/benefit analysis, suchas that developed for prawn stock enhancement in Western Australia(Loneragan et al., 2003). In any case, clear financial goals should be definedalongside quantitative measures of success for enhancement projects, providingan additional benchmark against which the success of a program can be gauged.These benchmarks should be set before commencement of the program.

USE ADAPTIVE MANAGEMENT

Adaptive management is a process for changing both production and manage-ment to control the effects of enhancement, thus allowing improvement overtime (Blankenship & Leber, 1995). An effective adaptive management processmay be difficult with many different stakeholders that are involved in a stock



TABLEIV

.Financialconsiderationsofstockingin

thecontextofcost/benefitanalysis

Stepsin

developingcost/

benefitanalyses*

Costsofstocking

Benefitsofstocking

Examplesofcost/benefitanalyses

1)Separate

development

cost

from

productionand

Initialcapitalandongoing

investm

ent

Valuingrecreationalfishing

Stocked

barramundi

inQueensland**

monitoringcosts

�Buildinghatcheryfacilities

�Aesthetic

values†

�64,50050mm

fingerlings

�Hatcherymaintenance

�Willingnessto

payand

stocked

inanim

poundment

(equipmentþ

healthsatandards)

contingentvaluation

�Each

recapturedfish

�Broodstock

managem

ent

analysis‡

valued

at$AU153

�Break-even

atc.1%

survival

2)Decidetheproportion

Planning

Valuingcommercialfishing

Stocked

reddrum

inTexas§

ofdevelopmentcoststhatare

�Runningworkshops

�Market

valueoffish

�15millionfingerlings

usable

inother

projects

�Developingmanagem

entplans

releasedper

year

orto

industry

�Pre-stockingsurveys

�Each

recapturedfish

valued

at$US445

�Break-even

at

c.0�01

%survival

3)Place

amonetary

value

Stocking

Other

benefits

Flatheadandwhiting

ontheharvestedproduct

from

�Healthassessm

ent

�Employmentin

inQueensland***

allsectors

involved

inthefishery

�Effectivetaggingoffish

ruralcommunities

�See

Table

IIIfor

�Fishtransport

�Creationof

numbersstocked

�Optimizationofreleases

new

industries

�Recapturedfish

cost

$AU17–24each

�Each

recaptured

flatheadvalued

at

c.$AU2.70

�Each

recapturedwhiting

valued

atc.

$AU1.70



TABLEIV

.Continued

Stepsin

developingcost/

benefitanalyses*

Costsofstocking

Benefitsofstocking

Examplesofcost/benefitanalyses

4)Monitorthenet

effect

Monitoring

ofstockingfora

�Fisheryindependentsampling

sufficientperiod

�Fisherydependentsampling

�Genetic

monitoring

�Resultsanalysis

�Communicationofresults

�Adaptivemanagem

ent

5)Estim

ate

regional/state

effectsasaresultofstocking

6)Convertallaesthetic

and

environmentalgainsto

monetary

values

inarobust

way

*Taken

from

Butcher

etal.(2000b).Forfurther

inform

ationsee†Fedler&

Ditton(1994),‡Cantrellet

al.(2004),**Rutledgeet

al.(1991),§R

utledge.

(1989)

and***Butcher

etal.(2000b).



enhancement program. A single body should be appointed by stakeholders tooversee and manage the program, especially if the program operates across stateor national boundaries.A system development matrix (Thom, 1997) is one practical approach to

evaluating the performance of a stocking project in an adaptive managementcontext. A simple example of this approach applied to a stocking project(Fig. 3), is for a situation where changes in the catch (or abundance) of prey,predator and stocked species provide the input for making management deci-sions. If the abundance of prey, stocked or competitor species alters from areference condition (catch rates immediately prior to stocking), then the matrixprovides some output to assist the management decision. A code of practice forstock enhancement in Australia, adapted as a flow chart (Butcher, 2001, Fig. 4),shows an adaptive management approach to marine stock enhancement. Suchan approach should ideally involve an initial assessment of the stock, evaluationof the ecosystem to determine if stocking is feasible, the development of thestocking program and consideration of the risks, and the monitoring of thestocking program. The key point of the framework (Fig. 4) is the feedbackloop from the monitoring and evaluation stage back into various stages of theprocess. The use of this code of practice (Fig. 4), combined with a matrix toassess the existing situation in the stocking program and provide feedback fordecision making (Fig. 3), will provide a feasible way to integrate adaptivemanagement into the stocking program. An alternative, more complex flow-chart is described in Molony et al. (2003), however this model does not allowpilot investigations of stocking to proceed before legislative changes are imple-mented. The potentially time-consuming process of legislative change may beuseless if pilot studies later reveal stocking to be unsuitable or unsuccessful.

AUSTRALIAN MARINE FINFISH ENHANCEMENT

Enhancement of freshwater fisheries in Australia began in Tasmania in 1861(Dix, 1987) and developed into stock enhancement programs undertaken byfishing clubs and governments in most states. Despite the relative success offreshwater projects, the enhancement of marine fisheries in Australia is still in itsinfancy and at present there are no ongoing marine finfish-stocking programs.There have been seven intentional releases of marine finfish into Australianestuaries all of which released <600 000 fingerlings over the course of the trials(Table III). Only four were monitored and can be considered as pilot studies(Fielder et al., 1999; Lenanton et al., 1999; Butcher et al., 2000a; Russell et al.,2004).

BARRAMUNDI IN NORTHERN QUEENSLAND

Barramundi (L. calcarifer) were the first marine finfish to be stocked andmonitored in Australia, beginning in 1986 for impoundments, and 1993 in opensystems (Rimmer & Russell, 1998). Fish were released into artificial impound-ments or inland lakes in an effort to create inland recreational fisheries, wherestocked fish did not reproduce naturally. Since the inception of this program



Define objectives ofresource management

Are there known production constraints?

Fisheries related constraints

Environmental/habitat related constraints

Is stocking an option?

Develop stocking strategy

Rearing techniques: •Growth rate

•Genetic integrity •Broodstock availability/

sufficient broodstock •Adequate

infrastructure

Conduct pilot-stocking trial & appraise results

Maintain status quo or consider alternative strategies

Implement stocking program

Monitoring & evaluation

Analyse cost-benefit

Define: • Stocking objectives

• Target species • Density/size

• Quality • Release strategy

Is stocking feasible?

Assess stock status Assess habitat status

Habitat modifications/ improvements

Review fisheries regulations

YES

YES

YES

NO

YESNO

REJECT ACCEPT

Assess status of stock

Plan, develop refine stocking

Stocking program

Is resource achieving set objectives?

Evaluate potential risks:

•Ecological •Genetic

•Environmental

FIG. 4. Stock enhancement code of practice (modified from Butcher, 2001). The process of stock enhance-

ment involves assessing the status of a fishery, planning and developing techniques for stocking.

Once this has been done, an adaptive management structure can provide for considerable refine-

ment of techniques and policies to increase both financial and environmental benefits, or avoid

future detrimental effects. Dashed lines represent areas where feedback can assist future manage-

ment decisions.



over 21 million fingerlings have been released and inland recreational barra-mundi fisheries have been created (A. Hamlyn, pers. comm.).Experimental stockings of barramundi in the Johnstone River aimed to pro-

vide information on size- and site-specific survival and cost-benefit. Almost 110000 coded-wire tagged fish (30–300 mm) have been released between 1993 and1999 (Table III, Russell et al., 2004). Early experiments indicated that size-at-release did not affect probability of recapture (Rimmer & Russell, 1998), how-ever the 1997–1999 stockings demonstrated that maximum survival was obtainedfrom releases of fish 300 mm long in an upper estuarine habitat, compared tofreshwater or estuarine habitats (Russell et al., 2004). Cost-benefit analysishowever, showed that to recoup the costs of the program as few as 0�8% ofthe 30 mm fish that were released would need to be recaptured (Rimmer &Russell, 1998) compared with 9�8% of the 300 mm fish (Russell et al., 2004).

SAND WHITING AND DUSKY FLATHEAD INQUEENSLAND

The Maroochy Estuary fish-stocking program was the largest marine stockingprogram undertaken in Australia, with approximately 432 000 sand whiting (S.ciliata) and dusky flathead (P. fuscus) released over three years (Table III,Butcher et al., 2000a). This study was based on some of the principles ofBlankenship & Leber (1995), and aimed to develop rearing technologies for thetarget species, and to stock and undertake a full-scale monitoring program toassess the effectiveness of stocking. Mass production of both S. ciliata and P.fuscus was achieved using controlled green-water larval rearing and extensivepond culture. Post-stocking mortality after one month was as high as 67 � 15%(mean; 39 � 11%), however the project examined alternative release strategies(i.e. stocking habitats) to minimize this. Oxytetracycline (OTC) marking trialswere unsuccessful, and scale-circuli analyses were developed to assess the originof recaptured fish. Recruitment to the commercial catch was as high as 28% forP. fuscus and 52% for S. ciliata, however the estimated cost of each fish wasaround 680% of the retail value (financial value of stocked fish to recreationalfishers was not monitored in this study). Although the stated aims were achieved,the project failed to show any increase in population size over the numbersestimated prior to stocking. The results may have been confounded by a largefish kill in the Maroochy estuary experienced during the project (Butcher et al.,2000b).

MULLOWAY IN NEW SOUTH WALES

A project was undertaken in 1997 by New South Wales Fisheries to evaluatethe production of mulloway (A. japonicus) juveniles using intensive and extensivetechniques, and to stock three intermittently closed-opening landlocked lagoons(ICOLLs) with approximately 75 000 A. japonicus juveniles (Table III, Fielderet al., 1999). This project was successful in rearing large numbers of A. japonicususing extensive techniques involving large (1 ha) earthen outdoor ponds.Hatchery reared fish were successfully labelled with OTC and released intothree coastal lagoons on the New South Wales coast (<5 m deep, <10 km2



area). Heavy post-stocking predation was experienced in one lake, and juvenilefish were observed swimming to sea after heavy rainfall in another, such that norecaptures were obtained from two estuaries. Fish were recaptured from SmithsLake at six, seven and nine months after stocking, and entered the commercialand recreational fishery 18 months post release. Fish grew at around 1 mm d�1

regardless of season, and recaptured fish were successfully verified as of hatcheryorigin by OTC marks. The small-scale release had an evident effect on the fisheryin Smiths Lake for several years following the stocking, with a 1500% increase intotal catch (catch averaged for four years before and four years after fish enteredfishery), compared to an overall decrease in total estuarine catch over the yearsfollowing the stocking (D. Makin, pers. comm.).

BLACK BREAM IN WESTERN AUSTRALIA

This pilot study aimed to determine the survival and growth rate of hatchery-reared black bream (A. butcheri) in the wild, and whether they entered therecreational fishery (Dibden et al., 2000). The study followed on from the releaseof 200 000 A. butcheri fingerlings into inland saline and freshwater impound-ments in Western Australia, to investigate the conditions that provided optimumgrowth and survival (Table III, Lenanton et al., 1999). Open system stockingconsisted of the release of 767, 14 month-old fish (�150 mm) tagged withexternal T-bar tags into the Upper Swan River. Twelve percent of these taggedfish were recaptured up to three years later by recreational fishers. The recap-tured fish showed a growth rate significantly higher than wild fish of the sameage, however the extent to which the stocked fish contributed to the recreationalfishery could not be determined as the number of wild A. butcheri caught was notmonitored throughout the experiment.Whilst these four projects addressed their respective aims, none have

addressed all 10 principles of the responsible approach (Table III). All but oneproject undertook marking and monitoring of stocked fish, two projects didsome economic modelling, and three attempted to optimize release strategies fora species (Table III). These pilot projects were aimed at addressing specific areasof the responsible approach, and this information could potentially be synthe-sized to form a larger study incorporating all of the 10 principles. Future stock-ing with suitable species in Australia should now aim to expand the preliminaryknowledge gained from these projects to address the core factors that are para-mount to successful stocking: stocking the appropriate environment with asuitable density of the correct species.

STOCK ENHANCEMENT: ECOLOGY IN A MANAGEMENT

CONTEXT

It is not an aim of this review to detail how stock enhancement should fit intothe overall management objectives for a fishery or ecosystem (Molony et al.,2003). Australia has recently adopted an ecosystem based management (EBM)approach to facilitate the ecologically sustainable use of Australia’s oceanresources (Alder & Ward, 2001). Molony et al. (2003) propose that stockenhancement be included in EBM by considering stock enhancement within a



hierarchy comprising individual fish stocks on the lowest level, and ecosystem orbioregion at the highest, with enhancement being targeted at individual fishstocks only. A four-component approach can be used to achieve this: (1) reviewall information about the ecosystem, fishery and stock involved; (2) compare andidentify fishery management tools available to be applied; (3) if stock enhance-ment is appropriate, develop objectives and processes along with experimentalpilot trials; and (4) if pilot work is successful, then full-scale stock enhancementcan proceed (Molony et al., 2003).Whether stocking can be undertaken in a sustainable fashion remains to be

seen, however it is possible that a correctly managed stocking program mayeventually overcome a recruitment bottleneck such that a stock can support itselfonce again. The stocking of marine finfish also provides the unique opportunityto address many core ecological assumptions and hypotheses that underpinfisheries management strategies (Miller & Walters, 2004). Precautionaryapproaches to stocking marine species (Molony et al., 2003) may often meanthat nothing is done in view of the potential risks. Rather than applying the strictprecautionary principle (Anon, 2000), a responsible approach to marine stockenhancement should allow stocking to proceed in a fashion that minimizes therisks of stocking on the ecosystem, satisfies the principles of EBM, and achievessocial and economic objectives especially in rural areas.

CONCLUSION: MAXIMISING THE BENEFIT AND SUCCESS

FROM STOCKING

The initial step in designing a stock enhancement program should be toidentify those ecosystems where there may be additional carrying capacity, andthen addressing which species to stock into that environment based on recruit-ment limitation and factors described in step one of the responsible approach(Fig. 1).While Australia’s commercial fishing production is low, representing only

0�2% of the world total (Kearney & Andrew, 1995), the Australian recreationalfishing industry is important to the economy. Almost 20% of the populationfished at least once during the 12 months prior to 2001, harvesting almost 27000 t of finfish. The industry was valued at $AU1800 million for that time period(for all recreational fishing, including �3000 t of invertebrates harvested, Henry& Lyle, 2003), while wild caught commercial fisheries for 2001 were valued at$AU1790 million (for all wild caught fisheries), with over 100 000 t of finfishharvested (ABARE, 2002).Examining the responsible approach in an Australian context reveals several

criteria that have the potential to both maximize the success and benefit ofreleases, and facilitate the further application of the ten-principles of marinestock enhancement. Whilst stock enhancement projects elsewhere have oftenconcentrated on stocking fish for capture in commercial fisheries, cost/benefitanalyses show that stocking of recreationally important species should increasethe benefit obtained from money invested (Rutledge, 1989; Rutledge et al., 1990,1991; Rimmer & Russell, 1998). With lower cost-benefit ratios, and the impor-tance of the recreational fishing industry in Australia, stocking recreationalspecies in urbanized ICOLLs protected from commercial fishing is feasible. By



stocking fast growing, estuarine residents such as mulloway and barramundi, atan acceptable density into recreational fishing havens, and refining techniquesusing ICOLLs as experimental units, Australia can apply responsible principlesto marine fish stock enhancement and achieve the maximum benefit fromstocking.

Thanks to A. Butcher at the Queensland Department of Primary Industries andFisheries for his helpful advice and comment through the preparation of this manuscript.This paper was funded in part from a grant from the New South Wales RecreationalSaltwater Fishing Trust and an ARC linkage project (grant #LP0219596). Many thanksto those individuals in other various government departments for assistance in assessingthe status of stock enhancement in Australia. Thanks also to two anonymous referees fortheir helpful suggestions.

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