Northern Pike Investigations Final Report (2012 2014)

Northern Pike Investigations

Final Report (2012–2014)

Prepared by:

Matthew Smukall, Biologist

September 2015

This project was made possible through two Alaska Sustainable Salmon Fund grants (Project

Numbers 45927 and 44629) received from the Alaska Department of Fish and Game and

through enhancement taxes paid by the commercial fishermen in Area H, Cook Inlet and

associated waters.

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DISCLAIMER

The Cook Inlet Aquaculture Association (CIAA) conducts salmon enhancement and restoration

projects in Area H, Cook Inlet, and associated waters. As an integral part of these projects a

variety of monitoring and evaluation studies are conducted. The following final report is a

synopsis of the studies conducted as part of the Alaska Sustainable Salmon Fund grant entitled

“North Pike Investigations.” Field research was conducted by Cook Inlet Aquaculture

Association and United States Geological Survey at Whiskey, Hewitt, and Chelatna lakes.

Laboratory research was conducted in Bozeman, Montana. The purpose of this report is to

provide a vehicle to distribute the information produced by the monitoring and evaluation

studies. The information presented in this report has not undergone an extensive review. As

reviews are completed, the information may be updated and presented in other reports. Product

names used in this report are included for scientific completeness, but do not constitute a product

endorsement.

Cook Inlet Aquaculture Association maintains a strong policy of equal employment opportunity

for all employees and applicants for employment. We hire, train, promote, and compensate

employees without regard for race, color, religion, sex, sexual orientation, national origin, age,

marital status, disability or citizenship, as well as other classifications protected by applicable

federal, state, or local laws.

Our equal employment opportunity philosophy applies to all aspects of employment with CIAA

including recruiting, hiring, training, transfer, promotion, job benefits, pay, dismissal, and

educational assistance.

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ACKNOWLEDGEMENTS

Many individuals contributed to the success of the Northern Pike Investigations Project.

Appreciation is extended to United States Geological Survey for assistance in the development

and operation of this project. In particular Dr. Adam Sepulveda, Megan Layhee, Brianna

McDowell, and Dr. Jackson Gross were vital to this project. Gratitude is extended to former

Cook Inlet Aquaculture Association (CIAA) staff members Karen Osterkamp for her role of

developing this project, Amy Shaw, who was instrumental in this project from the inception as

CIAA’s lead biologist, and to the many Cook Inlet Aquaculture Association interns, seasonal

assistants, and regular staff who invested many hours in planning and executing this project

especially Ron Carlson, Caroline Cherry, John Bailey, Emily Heale, Emily Marcus, Shane Eaton,

James Barley, Ross Lindholm, Joe Bottoms, and Richard Wells. Trail Ridge Air and Pollux

Aviation provided much needed assistance with hauling gear and supplies. Many local residents

of these lakes offered a great deal of help and were vital to the project, particularly Skwentna

Roadhouse and Chelatna Lake Lodge. Gratitude is also extended to the staff at the Alaska

Sustainable Salmon Fund, in particular Debbie Mass and Theresa Tavel; the Cook Inlet

Aquaculture Association’s Board of Directors; and to current CIAA staff member, Lisa

Ka’aihue, who provided oversight of the project.

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TABLE OF CONTENTS

DISCLAIMER ................................................................................................................................ ii

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

Table of Contents ........................................................................................................................... vi

List of Figures ............................................................................................................................... vii

List of Tables ................................................................................................................................ vii

List of Appendices ....................................................................................................................... viii

ABSTRACT .................................................................................................................................... 1

INTRODUCTION AND PURPOSE .............................................................................................. 3

PROJECT AREA ............................................................................................................................ 7

Whiskey Lake .............................................................................................................................. 8

Hewitt Lake ................................................................................................................................. 9

Chelatna Lake ............................................................................................................................ 10

METHODS ................................................................................................................................... 13

Objective 1: Determine northern pike seasonal movements, physical habitat, and water quality

parameters. ................................................................................................................................ 13

Objective 2: Conduct northern pike relative abundance, relative weight, sex, size, and age

structure in three lakes of the Susitna River basin (Chelatna, Whiskey, and Hewitt). ............. 15

Objective 3: Investigate effective methods to mitigate loss of salmon habitat and production

areas through targeted northern pike harvest goals in priority lakes......................................... 16

Objective 4: Continue ongoing beaver dam surveillance and mitigation for barriers to fish

passage/prevention of flooded vegetation conducive to northern pike. .................................... 16

Objective 5: Develop and assess the ability of NEPTUN barrier technology to influence pike

movement. ................................................................................................................................. 17

Objective 6: Assess the utility of electricity in eradicating pike embryos and larvae in lab and

spawning environments. ............................................................................................................ 23

RESULTS ..................................................................................................................................... 25

Objective 1: Determine northern pike seasonal movements, physical habitat, and water quality

parameters in Chelatna, Whiskey, and Hewitt lakes. ................................................................ 25


structure in Chelatna, Whiskey, and Hewitt lakes. ................................................................... 27

Objective 3: Investigate effective methods to mitigate loss of salmon production areas through

targeted northern pike harvesting. ............................................................................................. 31

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passage and to prevent the creation of flooded vegetation conducive to northern pike............ 33

Objective 5: Develop and assess the ability of NEPTUN barrier technology to influence pike

movement. ................................................................................................................................. 36

Objective 6: Assess the utility of electricity in eradicating northern pike embryos and larvae in

lab and spawning environments. ............................................................................................... 38

DISSCUSSION ............................................................................................................................. 39

CONCLUSION ............................................................................................................................. 45

REFERENCES ............................................................................................................................. 47

APPENDICES .............................................................................................................................. 51

List of Figures

Figure 1: Northern Pike Investigations project sites in relation to Cook Inlet, Alaska. ................. 7 Figure 2: Bathymetric map of Whiskey Lake. ................................................................................ 8

Figure 3: Bathymetric map of Hewitt Lake. ................................................................................... 9 Figure 4: Whiskey and Hewitt Lakes in relation to Yentna River. ............................................... 10

Figure 5: Bathymetric map of Chelatna Lake. .............................................................................. 11 Figure 6: Release sites of radio-tagged pike. ................................................................................ 14

Figure 7: NEPTUN fish barrier at Whiskey Lake. ....................................................................... 21 Figure 8: Diagram of NEPTUN fish barrier layout. ..................................................................... 21 Figure 9: Locations of radio tagged pike. ..................................................................................... 26

Figure 10: Length at age for Whiskey and Hewitt lakes, 2014. ................................................... 29 Figure 11: Length at age for Chelatna Lake, 2014. ...................................................................... 29

Figure 12: Kernel density estimate of length (mm) for Chelatna Lake. ....................................... 30 Figure 13: Polynomial representation of weights at length for pike harvested from Chelatna,

Hewitt, and Whiskey lakes 2012–2014. ........................................................................... 30 Figure 14: Sex ratios of northern pike harvested in 2014. ............................................................ 31

Figure 15: Gillnetting CPUE for the Whiskey and Hewitt lakes system. ..................................... 32 Figure 16: Chelatna CPUE 2010–2014......................................................................................... 32

Figure 17: Stomach contents of northern pike in Whiskey, Hewitt, and Chelatna lakes. ............ 34 Figure 18: Number of smolt and fry recorded in northern pike stomachs. ................................... 35 Figure 19: Passage rate of rainbow trout with NETPUN barrier. ................................................. 37 Figure 20: Northern pike responses to interaction with NEPTUN barrier. .................................. 38

List of Tables

Table 1: PIT-tagged, recaptured and harvested northern pike in the Whiskey and Hewitt lakes

system 2012–2014. ........................................................................................................... 28

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List of Appendices

Appendix 1: Southern end of Chelatna Lake and “Pike’s Pond” ................................................. 52 Appendix 2: Kernel density estimate of length (mm) for Hewitt Lake ........................................ 53 Appendix 3: Kernel density estimate of length (mm) for Whiskey Lake. .................................... 54 Appendix 4: Gillnet hours by lake and year. ................................................................................ 54 Appendix 5: Map of beaver dam notching and surveys. .............................................................. 55

Appendix 6: Voltage gradient of Whiskey NEPTUN barrier. ...................................................... 56 Appendix 7: Pike reactions to NEPTUN barrier........................................................................... 57 Appendix 8: Responses of pike to NEPTUN barrier as percentage. ............................................ 57 Appendix 9: Pike embryo response to 20-sec direct current electroshocking. ............................. 58

Appendix 10: Pike embryo response to 30-sec direct current electroshocking. ........................... 59

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ABSTRACT

Cook Inlet Aquaculture Association and United States Geological Survey conducted a 3-year

study to determine invasive northern pike (Esox lucius) population parameters, movement

patterns, habitat usage, and effective suppression efforts at 3 lakes in the Susitna River drainage

of Alaska. Northern pike preyed heavily upon juvenile salmon (Oncorhynchus) when available,

and pike were able to shift their diet when this prey was not available. Northern pike preferred

vegetated shallow water along the perimeter of lakes. Available habitat is likely to be a limiting

factor for pike populations. Population estimates for 2 of the study lakes revealed that while

Whiskey Lake is approximately one-half the size of Hewitt Lake, it has approximately 3 times as

many pike due to more available habitat. Density was estimated at 1.9 and 12.6 pike per acre in

Hewitt and Whiskey lakes respectively. Movement data indicated that relatively low rates of

travel by northern pike between these two lakes even though they are connected by a relatively

short and slow moving creek. Only 2.5% of radio-tagged (n=119) and 1.6% of passive integrated

transponder-tagged pike (n=1,395) moved from one lake to the other. A vertical pulsed direct-

current fish barrier called NEPTUN was tested for its effectiveness in blocking pike movement

and for any impact on native trout. Rainbow trout (Oncorhynchus mykiss) were able to pass

through the barrier with minimal long-term impacts, but there was avoidance with 98% of

juveniles and 84% of adults being repelled at least once when trying to pass barrier. In Whiskey

Creek, the barrier successfully blocked 64% of pike and trapped 4%, while 30% were able to

pass and 2% were stunned in the trials performed. Gillnets were most effective at catching pike

greater than 250 mm and fyke nets had the greatest catch rate of pike between approximately 125

mm and 300 mm. It may take multiple years of intensive netting to have noticeable impact on

pike populations, but netting does not appear capable of removing all spawners and therefore

will need to be used in combination with other suppression methods.

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INTRODUCTION AND PURPOSE

Nonnative species are altering aquatic communities worldwide, with opportunistic predators

having particularly catastrophic effects (Sepulveda et al. 2013). The introduction of northern pike

(Esox lucius) to freshwater systems outside their native range has resulted in negative impacts on

resident fish populations (Lee 2001, Patankar et al. 2006, Sepulveda et al. 2013). Outside their

native range, northern pike have the potential to interfere with ecosystem function and destroy

economically-important fisheries. In Alaska, northern pike are native north of the Alaska Range

(Marrow 1980), but were illegally introduced to the Matanuska-Susitna Valley in Southcentral

Alaska in the 1950s (Rutz 1999). Pike have spread to more than 130 water bodies in the

Matanuska-Susitna Valley, Anchorage, and the Kenai Peninsula (Alaska Department of Fish and

Game 2015). The Susitna River drainage covers tens of thousands of square miles and contains a

myriad of shallow lakes, sloughs, and clear water tributaries, many of which provide prime

northern pike spawning and rearing habitats.

Pike are voracious predators and it is hypothesized their expansion is responsible for the decline

of salmonid species in many water bodies in the Susitna basin (Rutz 1999, Patankar et al. 2006,

Sepulveda et al. 2013). Once established, northern pike can be devastating to juvenile salmonids

and have impacted numerous coho (Oncorhynchus kisutch), Chinook (O. tshawytscha), and

sockeye salmon (O. nerka) runs from the Susitna River drainage (Alaska Department of Fish and

Game 2015). Continual low returns to sockeye salmon were recorded in the main stems of the

Susitna River drainage. This led to the Alaska Board of Fisheries designating the Susitna River

sockeye population as a stock of yield concern in 2007. The Policy for the Management of

Sustainable Salmon Fisheries (SSFP; 5 AAC 39 222, effective 2000 amended 2001) defines

stock of yield concern as "a concern arising from a chronic inability, despite the use of specific

management measures, to maintain specific yields, or harvestable surpluses, above a stock's

escapement needs; a Yield Concern is less severe than a Management Concern." The SSFP

further defines chronic inability as “the continuing of anticipated inability to meet expected

yields over a 4 to 5 year period.”

In response to the recorded low returns of sockeye, Cook Inlet Aquaculture Association (CIAA)

and Alaska Department of Fish and Game (ADF&G) began to monitor salmon populations at

lakes throughout the Susitna drainage. Information was lacking about the health of salmon stocks

returning to lakes that previously did not have the presence of northern pike. From 2009 to 2013,

15 lakes were monitored for numbers of salmon returning to spawn. Historically, all of these

lakes had populations of returning salmon. Monitoring indicated that 8 of these lakes now had

northern pike populations, 4 of which no longer had returning salmon, and 3 lakes were found to

have salmon populations considered to be below historical averages. After realizing the extent of

the problem invasive northern pike have caused, CIAA developed a project entitled “Northern

Pike Investigations.” It was a 3-year project intended to help meet CIAA’s ultimate goal for the

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Susitna River Valley of increasing salmon production by removal of northern pike and

rehabilitation of lakes throughout the system. This project was designed to determine northern

pike movements, habitat preferences, and the most effective sampling methods that will help

establish the best mitigation plan for individual lakes and recovery of salmon stocks in many

severely impacted systems throughout the Susitna River basin.

Efforts have been underway to suppress pike populations with gillnets in some priority systems

within the Susitna River basin. There is some evidence that gillnets may be effective to suppress

pike numbers enough to provide recovery of salmon populations (Rutz 2014). These recovery

efforts are likely to be limited in scope and require annual gillnetting efforts to keep pike

populations suppressed. Gillnets are labor intensive, indiscriminate, and typically only capture

fish greater than 200 mm (depending on the mesh size). Due to the inability to catch smaller-

sized pike, gillnets are incapable of completely extirpating the fish from a system. Continual

netting is required to maintain pike at suppressed levels. Smaller northern pike, potentially

missed by gillnetting, are the primary consumers of juvenile salmonids (Sepulveda 2012) and

targeting this size class is vital to successful suppression efforts.

The success of suppression and eradication efforts may be limited by the ability of northern pike

to recolonize systems. Suppression efforts may open niches within systems that support an influx

of pike from other areas. Eradication efforts can only be successful if there is assurance pike will

not repopulate the system from surrounding areas. The Susitna River drainage is a vast area with

highly connected swampy areas, and therefore complete eradication from the system is

improbable. However, successfully extirpating pike from priority systems may be possible

through a combination of netting and rotenone application. There is a need for the development

of alternate northern pike control technologies to prevent recolonization of water bodies where

suppression has taken place and to prevent the expansion to other connected systems.

The use of electrical fields to alter the movement of aquatic fish has occurred since at least the

1920s in North America (Baker 1928), with large-scale applications beginning in the 1950s

(Ostrand et al. 2009, Clarkson 2003). Initially, electric barriers used alternating current (Baker

1928; Applegate et al. 1952; Johnson et al. 2014) but the rapid reversals of polarity resulted in

high mortality to nontarget species (Johnson et al. 2014, Reynolds and Kolz 2012, Erkkila et al.

1956). Conversely, the likelihood of mortality is reduced when using pulsed direct current (PDC)

(Reynolds and Kolz 2012, Johnson 2014). In the 1950s, PDC was used to successfully block

upstream spawning migrations of sea lamprey (Petromyzon marinus) (Mclain 1957). Although

this early PDC array was constructed with vertical electrodes (McLain 1957), most PDC barriers

are now designed with horizontal electrodes (Johnson 2014). Both vertical and horizontal

electrode designs have advantages and disadvantages. Horizontal electrodes can be mounted to

the stream bed to allow for easier passage of boats and debris, but because the electrical field

dissipates with increased distance from the electrode there is potential for the field to be weak

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enough at the surface to allow for unintended fish passage (Johnson 2014). Vertical barriers

provide a more consistent electric field in the water column and can be quickly installed with

minimal modification to the stream bottom, but inhibit passage of watercraft (Johnson 2014).

With advancements in technology, these vertical PDC barriers are relatively portable and can be

powered with small generators. It is now possible to install these barriers on remote waterways

with very limited access.

For systems with both native and invasive species, a complete blockage of the waterway is not

feasible because the native fish need to be allowed to migrate, especially salmonids. Designing

PDC barriers that guide fish into “live-boxes,” faraday cage enclosures shielded from the

electrical field, would allow for sorting of native and nonnative fish species. Previous research

with the NEPTUN vertical electric barrier proved to successfully block sea lamprey migration

and directed them into traps (Johnson et al. 2014).

Current netting efforts predominantly capture adult pike. There is a need for effective methods to

target offspring and prevent future generations from continually replacing adult pike once

removed. Pike spawn in slow moving, shallow water bodies and after egg deposition eggs attach

to substrate or to submerged macrophytes (Mecozzi 1989). Application of electricity in these

critical spawning grounds could be an effective means of decreasing new generations of invasive

pike. Electricity has been shown to effectively induce mortality in eggs of several species of

freshwater fish (Bohl et al. 2010, Nutile et al. 2013). This research demonstrates that electric

field intensities (voltage), exposure duration, and embryo size can influence fish embryo

susceptibility to electricity. However, there is no information on the susceptibility of northern

pike embryos to electricity.

To investigate methods to maximize pike suppression efforts, CIAA and United States

Geological Survey (USGS) developed a project entitled “Northern Pike Control Investigations.”

Funding for this project was awarded to CIAA and USGS through the Alaska Sustainable

Salmon Fund. The objectives of this project were:

1. determine northern pike seasonal movements, physical habitat, and water quality

parameters,

2. conduct northern pike relative abundance, relative weight, sex, size, and age structure in

three lakes of the Susitna River basin (Chelatna, Whiskey, and Hewitt),

3. investigate effective methods to mitigate loss of salmon habitat and production areas

through targeted northern pike harvest goals in priority lakes,

4. continue ongoing beaver dam surveillance and mitigation for barriers to fish

passage/prevention of flooded vegetation conducive to northern pike,

5. develop and assess the ability of NEPTUN barrier technology to influence pike

movement, and

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6. assess the utility of electricity in eradicating pike embryos and larvae in lab and spawning

environments.

This project took place from April 2012 to April 2015. The purpose of this report is to present

the results of the Northern Pike Control Investigations Project.

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PROJECT AREA

Whiskey, Hewitt, and Chelatna lakes are located in the Susitna River drainage in Southcentral

Alaska (Figure 1).

Figure 1: Northern Pike Investigations project sites in relation to Cook Inlet, Alaska.

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Whiskey Lake

Whiskey Lake is located at 61º59’ W latitude and 151º24’ N longitude at the base of the Shell

Hills in the Susitna River drainage, approximately 118 kilometers northwest of Anchorage,

Alaska (Figure 1). It has an elevation of 45 meters and a surface area of 110 hectares (Figure 2)

(Spafard and Edmundson 2000). There is one small unnamed tributary of Whiskey Lake located

on the north side of the lake. The lake’s discharge forms Whiskey Creek, which flows into

Hewitt Creek and the Yentna River. The latest adult salmon count for Whiskey Lake was in 2010

with 59 sockeye, 1 coho, 22 pink, and 40 chum salmon returning. An aerial survey indicated

there were also a large number of salmon, potentially up to 600, spawning downstream of the

enumerating weir location (Weber 2011).

Figure 2: Bathymetric map of Whiskey Lake.

Contours in meters.

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Hewitt Lake

Hewitt Lake (Figure 3) is located approximately 0.5 km to the east of Whiskey Lake (Figure 4).

Hewitt Creek is a common outlet for both Hewitt Lake and nearby Whiskey Lake, and flows 6.4

meandering kilometers to the Yentna River. Hewitt Lake covers 226 hectares, has a maximum

depth of 34 m, a mean depth of 13.5 m, a 10.6 km shoreline, and is located at an elevation of 40

m above sea level (Spafard and Edmundson, 2000). The most recent adult salmon monitoring

project at Hewitt Lake occurred in 2006 with 2,507 sockeye salmon returning (Weber 2010).

Figure 3: Bathymetric map of Hewitt Lake.

Contours in feet.

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Figure 4: Whiskey and Hewitt Lakes in relation to Yentna River.

Chelatna Lake

Chelatna Lake is located at the base of the Alaska Range approximately 160 km north-northwest

of Anchorage (Figure 1). It has a surface area of 1,581 hectares, a maximum depth of 125 m,

mean depth of 61 m, and 27 km of shoreline (Figure 5) (Spafard and Edmundson 2000). The

outlet, Lake Creek drains south from the Chelatna Lake. Chelatna Lake is one of the 3 main

sockeye salmon producing lakes in the Susitna River drainage, with the other 2 lakes being Judd

and Larson. From 2009 to 2014, an average of 43,222 adult sockeye salmon returned to Chelatna

Lake (CIAA 2013, Munro and Volk 2014, Shields and Dupuis 2015).

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Figure 5: Bathymetric map of Chelatna Lake.

Contours in feet.

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METHODS

Objective 1: Determine northern pike seasonal movements, physical habitat, and water

quality parameters.

Seasonal movement patterns were determined at Whiskey and Hewitt lakes using radio tags and

passive integrated transponder (PIT) tag recaptures. Radio tags were Lotek MST-930 coded

internal radio tags and tracking took place with Lotek SRX 400 telemetry receivers. Biomark

12.5 mm FDXB and Oregon RFID 23 mm HDX PIT tags were used in this study. Northern pike

for tagging were captured from Whiskey and Hewitt lakes with gillnets and hook and line

fishing. Capture methods are described in greater detail under Objective 2. No seasonal

movement patterns via tagging studies were done at Chelatna Lake.

Implantation of 119 radio tags occurred in July and August of 2012. Gillnets were placed at sites

around Whiskey and Hewitt lakes in an attempt to capture pike evenly through the system.

However, certain locations had higher catch rates and therefore had more pike tagged at those

locations. Captured fish were anesthetized in a 60 L tank containing water that has been enriched

with clove oil at a concentration of 25 g/60 L. A battery powered air stone aerator was used to

ensure tank water remained oxygenated and the tank was positioned in a shady place to prevent

the water from becoming too warm. Water was refreshed in tank if it reached a temperature 2˚C

greater than the lake water. Once a fish lost equilibrium (typically 3–5 minutes), it was removed

from the anesthesia tank and placed ventral side up on V-shaped foam cradle covered with a

sterilized plastic sheet to minimize mucous loss. Clove oil-enriched water at a concentration of 4

g/60 L was circulated over the gills in order to maintain anesthesia during surgery. A 10–20 mm

incision through the skin and muscle was made using a number 10 scalpel blade on the ventral

body surface, posterior to the pelvic fins, and slightly off the midline. A scalpel was used to

penetrate the peritoneum, and straight blunt scissors were used to widen the peritoneal incision,

with extreme care taken to avoid injury to internal organs. A spinal needle was used to puncture

an exit hole for the radio antenna approximately 10 mm posterior of the incision. The transmitter

was placed in the abdominal cavity and positioned posterior to the incision to avoid placing

pressure on the sutures. The tag end of the antenna was gently pulled to help position the tag and

ensure any slack antenna was on the outside of the fish. Incisions were closed using 3–5 simple

interrupted sutures of absorbable suture material and a 24 mm curved cutting needle. Surgery

times averaged approximately 4–5 minutes. After each individual surgery instruments were

disinfected using betadine. Immediately following surgery, fish were transferred to a holding pen

in the lake. Fish were monitored after surgery to ensure that they regained equilibrium and were

ventilating properly prior to release. Once the northern pike fully recovered they were held for a

few hours before being returned to their location of capture (Figure 6).

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Figure 6: Release sites of radio-tagged pike.

Numbers indicate the number of pike released to that location.

Northern pike were released to the same location where they were captured.

Field crews used standard radio telemetry techniques to track tagged fish on average twice per

week using a 14 ft skiff. Crews slowly idled parallel to and approximately 30 m from shore.

Once the shoreline was surveyed, the remainder of the lake was covered with a grid-like pattern.

When a tag was detected, crews got as close to the exact location as possible and recorded it with

a Garmin GPS. Vegetation and water quality sampling were conducted at that location (see

physical habitat and water quality sections).

Additional information on movement patterns within and between lakes was determined by

comparing recapture locations of PIT-tagged pike to previous capture locations. For details on

PIT tagging procedures see Objective 2.

Physical habitat parameters in Whiskey and Hewitt lakes were determined at tracking locations

and predetermined sampling sites. In Whiskey Lake there were 60 predetermined sampling sites,

68 in Hewitt, and 38 in the Whiskey–Hewitt creek system. The majority of the sites were located

in the littoral zones of Whiskey and Hewitt lakes; however, there were some sites in the limnetic

zones of each lake. In Chelatna Lake and the first 4 miles of Lake Creek, 153 sites were

surveyed. Vegetation and water quality surveys were performed at each predetermined site 3

15

times per field season (May–October). Sampling events occurred once during each sampling

season—early summer (May–June), mid-summer (July–August), and early fall (September–

October). Sampling occurred at tracking locations on the day of or day after a pike was located in

that location.

Vegetation and water quality surveys were performed from a 14 ft skiff using a Garmin GPS to

ensure the crew was within 10 m of the sampling site. The boat was gently anchored as to not

disturb the sediment. Depth was determined by attaching a weight to a line with every one-half

meter marked. The weight was lowered to the bottom and the marking on the line at the surface

was recorded. A Secchi disk was then attached to the line and was lowered in the water column

until disappearing from view. It was then lowered one-third of a meter more and slowly retrieved

until it just reappeared. The disk was slowly moved up and down until the exact vanishing point

was found. Using an YSI ProODO meter, temperature and dissolved oxygen were measured

subsurface and then every one-half meter thereafter.

Physical habitat sampling was conducted using a double-sided vegetation rake and visually

determining the substrate when possible. The rake was thrown 10 m from the boat toward shore,

allowed to sink to the bottom, and retrieved to the boat. The percent of rake teeth filled and the

percent abundance of individual plant species were recorded. Vegetation was also classified as

submersed, rooted floating leaved, nonrooted floating leaved, emergent, and without vegetation.

When visible, the substrate at each sampling site was recorded as silt/clay, mostly silt with sand,

mostly sand with silt, sand, gravel/cobble, hard clay, or boulder.


structure in three lakes of the Susitna River basin (Chelatna, Whiskey, and Hewitt).

Relative abundance of northern pike was determined using capture-mark-recapture in Whiskey

and Hewitt lakes with a closed population model approach. Pike were captured in gillnets (1-in

bar, 50 ft length, and 8 ft deep). On initial capture all pike from the Whskey–Hewitt system were

PIT tagged. Once removed from the gillnet, pike were transferred to a tote filled with lake water.

Fish were secured in a V-shaped measuring board and fork lengths recorded to the nearest mm.

Fish were then rolled so that the ventral side was exposed. A PIT-tag gun with a hollow needle

was used to inject preloaded PIT tags into the abdomen. Needles were inserted at a 10 to 20

degree angle and directed to the posterior to avoid piercing any organs. Fish were scanned with a

PIT-tag reader to ensure the PIT tag was working and the number was verified. Before releasing

the fish, scales were removed from just above the midline of the fish in line with the pelvic fins.

Scales were cleaned of debris and slime and placed on a gum scale card. Aging of scales

occurred after field season. Fish were then weighed to the nearest 10 gm and released to the

original capture location. In Hewitt Lake, 325 northern pike were marked, 741 in Whiskey Lake,

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and 299 in the Whiskey–Hewitt Creek outlet. Any recaptured fish had tag number, location,

length, and weight recorded.

At Chelatna Lake, pike were captured using gillnets, fyke hoop nets, and hook and line. Pike

were harvested over the duration of the project. Captured pike were removed from the net and

quickly dispatched by striking them on the head with a small bat. Length to nearest mm, weight

to 10 gram, and sex were recorded. Scale samples and one cleithrum were removed for aging.

Stomach contents were recorded based on percent of total volume. Categories were sockeye

smolt, coho smolt, other salmonid, stickleback, partial fish, insects, leeches, snails, trout, or

other. If salmon smolts were identified in the stomach contents, a count of the number of smolts

was recorded. Weight to the nearest 0.1 g was recorded for each category. Harvested pike were

donated to local residents or cut in half and disposed of in the middle of the lake in accordance

with permits.

In 2013 and 2014, northern pike were not harvested at Whiskey and Hewitt lakes in order to

perform the tracking and abundance studies. However, in 2014, all pike captured at the

Whiskey–Hewitt system were harvested and worked up similar to the Chelatna Lake protocol.

Tag numbers for any previously tagged fish were recorded.

Objective 3: Investigate effective methods to mitigate loss of salmon habitat and production

areas through targeted northern pike harvest goals in priority lakes.

Catch per unit of effort for gillnetting, hook and line, fyke hoop nets, and minnow traps were

compared at all lakes. Capture efforts were focused on habitat types that are known to be

conductive to pike—shallow and vegetated waters. Effort time for each of these methods was

recorded to the nearest 0.25 hour and catch rates of pike were recorded.


passage/prevention of flooded vegetation conducive to northern pike.

Beaver dam surveys have been performed on tributaries in the Susitna River watershed, and

occasionally other Cook Inlet drainages for many years by CIAA. Surveys were conducted on

creeks with known histories of problematic beaver dams (that is beaver dams that impede fish

passage) or when notified by ADF&G and other organizations of potential beaver dam issues.

During this study at least 2 surveys were performed each summer for all 3 years of the study

during the adult sockeye salmon return, usually in late July or early August and again in mid-

August. Crews flew creeks at low altitude in a Robinson R44 helicopter. When a beaver dam was

spotted the helicopter hovered low enough for the crew to assess if salmon were downstream of

the dam and if the dam appeared to be blocking passage. Fish blockage was usually the result of

not enough water flowing over the dam (in that case salmon could become trapped on or in the

17

dam debris) or not a deep enough pool at the base of the dam to allow for salmon to build up

sufficient speed to jump and clear the dam. If the dam was determined to be blocking fish

passage, the helicopter landed and the crew notched the dam. The temporary notch was made

wide enough to provide sufficient water flow for salmon to jump the dam.

Objective 5: Develop and assess the ability of NEPTUN barrier technology to influence

pike movement.

Bozeman Testing

The effects of the NEPTUN fish barrier on juvenile and adult rainbow trout were tested by CIAA

and USGS. All experiments were conducted at the US Fish and Wildlife Service Bozeman Fish

Technology Center (BFTC), Bozeman, MT in January–February 2013.

Trout were housed in circular tanks (1.9 m diameter x 0.75 m height) with recirculating water at

13.77 ± 1.02 °C (mean ± 1 SD) through the duration of experiments. The care and maintenance

of these trout were in compliance with BFTC standards. Trout were tagged with PIT (Biomark,

Inc., Boise, ID) tags prior to experiments and held for 24–48 hours (henceforth, h) to ensure that

any harm (e.g., mortality, bruising) was not due to handling. Dipnets were used to transfer fish

between housing, holding and experimental tanks. Fish weight (to nearest tenth of g) and fish

length (to nearest mm) were measured prior and post (0.5, 192 h) experiments.

All experiments were conducted within an artificial oval shaped stream channel (20-m

circumference x 1.2-m deep x 1.55-m wide) that was filled with waters originating from cold and

warm springs and circulated through a re-use system. Water depth was 0.9 m, average (± 1 SD)

water temperature in the stream channel was 13.77 ± 1.02 °C, water conductivity was 409.4 ±

26.9 µS/cm, dissolved oxygen was 7.88 ± 0.51 mg/L, and pH was 7.97 ± 0.04. The stream

channel contained a cobble substrate and the channel flow velocity was near 0 m/s.

The NEPTUN barrier was installed as a symmetrical vertical barrier system. A series of 3

electrode curtains were placed across the width of the stream channel. Each electrode curtain was

separated by 1.2 m of stream channel. The 2 outermost curtains were composed of 3 positive

electrodes, each spaced 0.6 m apart, and the center curtain was composed of 2 negative

electrodes spaced 0.7 m apart. This barrier design created an electrical field on both sides of the

center curtain. The electrodes were steel pipes that were suspended from above the water’s

surface and extended to the bottom substrate. The barrier system was connected to a power

supply using a PDC waveform with a range of output voltages (V) and pulse width in

milliseconds (ms). The NEPTUN electric barrier was configured to run at three different output

voltages (V) at various pulse widths (ms) and duty cycles (%).

18

Volitional trout movement in relation to the barrier as a function of voltage, pulse width, fish life

stage and fish length was assessed. Three output voltage settings (51.4 ± 0.53, 69.0 ± 0.76, and

91.4 ± 1.65 V) were used at 3 pulse widths (with corresponding duty cycles %) including 0.1 ms

(0.3%), 0.4 ms (1.3%), and 0.7 ms (2.3%), and controls (0 V, 0 ms, 0% duty cycle) totaling 10

electrical settings (Table 1). It was not possible to evaluate voltage independent of pulse width

because voltages at 0.0 V have a 0.0 ms pulse width. Juvenile trout (92.4 ± 11.5 mm; fork length

mean ± SD) and adult trout (307.5 ± 39.6 mm) were exposed to the 10 barrier settings.

The extent and intensity of the electrical field and peak voltage gradient (V/cm) were measured

and verified using an oscilloscope and forked probe (10-cm distance between probe ends) prior

to each individual fish exposure. Peak voltage gradient was measured midway between the first

positively charged curtain and the middle negatively charged curtain. To determine when a fish

interacted with the barrier, the extent of the electric field was determined by detecting the edge

of the field with the oscilloscope.

Individual fish from the holding tank were transferred to an aquarium tank, where PIT-tag

identity was determined, fish were measured for weight and length, and assessed for condition,

defined as an individual’s general appearance and behavior. Bruising, deformities, or lesions

were noted and only fish that demonstrated appropriate responsiveness to stimuli and normal

orientation and swimming behavior were included. Fish were placed in buckets (19 L) for 2

minutes prior to being gently poured into the stream channel 1 m away from the beginning of the

electric field. Fish behavior was observed and documented by one observer for 5 minutes. Fish

behavior in relation to the barrier was volitional and recorded as “pass,” “deflect,” and “stun.” A

pass referred to a fish moving completely through all three curtains of the electrical barrier.

Deflect referred to a fish entering the electrical field, turning around and leaving the barrier the

same way it entered—a reactive detection of the electric field. A stun occurred when a fish

entered the electrical field and was unable to remove itself, showing signs of narcosis. After 5

minute, the barrier was turned off and fish were removed from the stream channel. If the fish

passed through the barrier or became stunned, the barrier was turned off and the fish was

removed from the stream channel. Fish weight, length, condition, and mortality were assessed

0.5 h and 192 h after experiments. Only injuries associated with electricity (brands) were

included in analysis.

Juvenile trout were used one time during the duration of the experiment, and adult trout were

used twice. The experimental unit was a trial, where a trial consisted of all possible voltage ×

pulse width combinations randomly assigned to 10 juvenile trout or 10 adult trout. Eight trials

were conducted on juvenile trout over 3 continuous days and 8 trials were conducted on adult

trout over 8 days. All the adult trout were used during 4 trials on day 1 of experiments and then

rested for 7 days before completing 4 additional trials with the same fish on day 8 of

experiments.

19

To test if the NEPTUN fish barrier injured juvenile trout, juvenile trout (86.8 ± 13.0 mm) were

exposed to the NEPTUN’s electrical field for 20 seconds (s) using 3 voltage settings (51.4 ± 0.3,

69 ± 0.5, and 91.5 ±0.6 Volts) at 4 different pulse widths 0.1 ms (0.3% duty cycle), 0.4 ms

(1.3%), 0.7 ms (2.3%), and 1.0 ms (3.3%) with controls (0.0 V, 0 ms, 0 %). Pilot data indicated

that 20 s was the maximum time a juvenile trout spent within the 3-curtain barrier when it was

on. The electrical field was verified and the voltage gradient determined using an oscilloscope

prior to each individual exposure. Individual fish were placed in a mesh bag and pulled through

the NEPTUN barrier at a constant velocity for a 20 s exposure time. Physical condition and

mortality were assessed 0.5 h and 192 h after experiments with the following physical

abnormalities noted; bruising (e.g., electrical brands), bleeding, loss of equilibrium, or any other

notable behaviors.

The R platform was used to conduct all statistical tests (R Studio, v. 0.98.501, R Core Team

2014) with a 95% confidence interval. The student’s t-test was used to compare the number of

control and treatment juvenile and adult trout that passed the barrier. Generalized linear models

(GLM) were used to test if fish passage (binary response—pass or no pass) was a function of

voltage, pulse width, life stage, and length. Experiment day and trial number were included in

the model as random effects. Voltage, pulse width, life stage, and length were discrete

variables. To test for overdispersion, models were run with quasibinomial distribution. The

anova function in R (with Chi-squared test option) was used to assess significance of each model

term and the change in deviance with the addition of each term. To make pairwise comparisons

between voltage and pulse width levels Tukey-HSD posthoc tests (glht function in R) were used.

Student’s t-tests were also used to compare number of deflections between juvenile and adult

trout. Analysis of covariance (ANCOVA) was used to test if the number of deflections was

related to barrier passage for juvenile and adult trout. Fish length was used as a covariate of

number of deflections. ANCOVA was also used to test for an effect of voltage, pulse width, and

volitional behavior (pass, deflect) and to test if passage and bruising in adult trout on day 8 of

experiments were a function of the voltage, pulse width, number of deflections, passing or

bruising experience by adult trout on experiment day 1. Length was the covariate. Normality for

all variables was assessed using Shapiro-Wilk tests.

Whiskey Lake Testing

To determine the utility of the NEPTUN fish barrier at blocking the movement of northern pike,

testing was conducted from mid-May through mid-July, primarily at night. To avoid any

potential negative influence on native fish the NEPTUN barrier was operated during the day

from June 1 through July 15, 2013. This study was operated in compliance with Fish Habitat

Permit FH-12-IV-1209 from ADF&G. A smolt weir was operated by CIAA at the outlet of

Whiskey Creek blocking any fish passage from the lake into the creek while the NEPTUN was in

operation and a temporary net was placed downstream of the barrier during testing. There was

20

minimal to no movement of pike from downstream into the NEPTUN testing area (A. Shaw, M.

Smukall, CIAA unpublished data) and it was assumed no fish naturally moved into the NEPTUN

study site while the tests were being conducted each day. The substrate at the study site was

primarily gravel and small stones with some debris such as logs and sticks.

The NEPTUN vertical barrier system was constructed in Whiskey Creek at a 45˚ angle from the

bank. Duckbill anchors were used to anchor ¼” galvanized cables strung across the creek. Cables

were ~20 m long with ~15 m over water. At each end, a ratchet strap or come-along was

connected between an insulated eye loop on the cable and the eye loop on the anchor. The ratchet

strap and come-along were used to tighten the cable so there was no sag in the middle, this was

checked, and adjusted daily to ensure the cable was taut. All 3 cables (2 positive, 1 negative)

were run parallel and installed in an identical manner with approximately 1.5 m spacing between

each cable. On the 2 outermost cables (positive), electrodes were hung from the cable

approximately every 1.2 m. Electrodes were hung from the center cable (negative) approximately

every 1.5 m.

A pass over PIT antenna was constructed upstream and downstream of the barrier system. The

antennas were constructed from 4 gauge copper wire (car battery cable) and each antenna loop

was approximately 20 m long (40 m total length). Each antenna began at a tuner box located on

the creek bank, the cable ran parallel to the electrodes but just outside of the electric field

(determined by oscilloscope) to avoid interference. Upon reaching the other creek bank the cable

returned to the tuner box, running parallel to itself at a distance of 1 m to form a long, slender

loop. Cable loop was held to the stream bed with fiberglass stakes. Read range for the PIT

antenna was up to a height of 0.75 m above the creek bed. The 2 tuner boxes were connected to

an Oregon RFID reader box that recorded any PIT tag passes and could be downloaded to a PC.

Two live boxes, approximately 2 m long and 1 m wide, located at each end of the barrier were

constructed with 1.9 cm galvanized pipe placed through two 7.6 cm aluminum channels per side.

Pipes were approximately 1.5 m in length with 2.54 cm between pipes. On the end of the live

box facing away from the center of the electrical field, a “V-shaped” funnel was created to guide

fish into the live box (figures 7–8). The live boxes were also wrapped with 3.8 cm wire mesh to

better act as a faraday cage and protect any fish in the live box from electrical current. The live

box on the near shore was designed to capture pike attempting to move up stream that had been

guided by the barrier system. The live box on the far shore was intended to capture pike moving

downstream and guided by the barrier.

There was minimal flow in the creek moving from left to right.

21

Figure 7: NEPTUN fish barrier at Whiskey Lake.

Figure 8: Diagram of NEPTUN fish barrier layout.

22

The NEPTUN system was powered by a gas 3000 W generator (Honda EU3000iS Inverter) and

stored in a Rubbermaid deck box to protect from weather. A grid was created with twine strung

across the creek (at a right angle from the bank) and spaced 1 m apart. Markings were placed

every 1 m on the string in order to create 1-m by 1-m cells. An oscilloscope with a forked

voltage probe (10 cm distance between probe ends) was used to measure the intensity (V cm-1

peak voltage, not the average of one cycle) of the field at the center of each cell in the grid.

Northern pike were caught from Whiskey Lake with either rod and reel or gillnets (2.54 cm bar).

Fork length (mm) and weight (nearest 10 gm) were recorded. Crew injected PIT tags into the

body cavity of each pike. Pike were held in a 1-m by 2-m pen over night at the outlet of Whiskey

Lake. Mortalities were discarded in Whiskey Lake in accordance with fish resource permits.

Injured or noticeably ill pike were not used in the study.

Prior to each trial, the PIT-tag number was recorded for each pike to be used. The fish were

transported from the holding pen in plastic “live bags” to the study site in the creek,

approximately 50 m. For each trial, 5 pike were released upstream of the barrier (within 5–10 m)

and 5 were released downstream of the barrier (within 5–10 m). Pike were allowed to acclimate

in the creek for 2 hours with the electric barrier turned off. The NEPTUN barrier was then turned

on for 2 hours and interactions with the barrier were recorded. The interactions were classified as

(1) “pass” when pike successfully made it from one side of the barrier to the other; (2) “repel”

when pike interacted with the barrier and were repelled back to the side of the creek they

originated from; (3) “trap” when pike were successfully funneled into the live box; and (4)

“stun” if pike entered the barrier and were stunned, rolled belly up, and were unresponsive.

Stunned pike were either swept downstream of the barrier by the current or removed by

observers. The NEPTUN barrier was operated at a setting of 100 voltage, with a pulse width of

2.4 ms, time between pulses of 10 ms, packet time of 50 ms, time between packets of 150 ms,

and a total duty factor of 8%.

A combination of visual observation, video recording, and PIT-tag recordings were used to

determine when pike interacted with the barrier and their response. The bank on Whiskey Creek

is fairly steep (>45˚) and observers were able to stand 3–5 m above the creek to get an adequate

vantage point. A camera was suspended from a cable approximately 10 m above the creek to

visually record pike movements. The camera was positioned above the center of the barrier with

a series of pulleys on the cable. Due to the ultra-wide angle of view (170˚), the video recordings

visually covered the entirety of the barrier system. Videos were analyzed at a later date to verify

field observations. The PIT antenna reader box also had a buzzer to alert observes when a tagged

pike was passing over the antenna. Data of the individuals passing over the antennas were

downloaded from the recorder at a later time. Pass, repel, stun, and trap rates of each trial were

taken and then averaged over all 15 trials.

23

Following the NEPTUN testing, the barrier system was turned off and the pike were removed

from the area. Fish were released back into Whiskey Lake, as part of the habitat usage and

movement studies.

Objective 6: Assess the utility of electricity in eradicating pike embryos and larvae in lab

and spawning environments.

Experiments were conducted in a laboratory facility at U.S. Geological Survey’s Northern Rocky

Mountain Science Center (NOROCK) in Bozeman, MT. to (1) determine voltages that cause

100% mortality in pike embryos and (2) determine if varying exposure duration (seconds) alters

mortality rates in pike embryos. Approximately 15,000 northern pike embryos were acquired

from Fort Peck State Fish Hatchery, Fort Peck, MT. Average embryo diameter was 2.81 mm (±

0.12; SD) and embryos were in the eyed-stage of the embryonic phase (Raat 1988). Embryos

were housed in a 50-gallon holding tank with recirculating UV-sterilized water in the laboratory

facility at NOROCK. Upon receiving the embryos, water originating from the holding tank was

slowly introduced to the transport container and water temperature was regulated in the holding

tank using a chiller to achieve optimal temperatures (9–15°C; Hassler 1982). Water quality

condition in the holding tank was monitored using YSI ProODO Plus. Dissolved oxygen levels

were on average 10.1 mg/L (± 1.0; SD), water temperature was 9.98 °C (± 0.23), and

conductivity was 162.5 µS/cm (± 5.48).

Homogenous electric fields were generated with the Aqua Shock power control box designed by

Aqua Shock Solutions. Two parallel steel electrodes (14-cm wide x 18-cm tall) were mounted in

a glass aquarium (30 cm x 15 cm x 19 cm) with 2 cm water depth. Electrodes were placed 12 cm

apart. The anode and cathode cables were connected with alligator clips from the Aqua Shocker

power control box to either electrode. The control box provided straight direct current (DC).

The power supply had 11 voltage settings. Once the appropriate voltage setting was selected, the

corresponding output voltage (V) and amperage (mA) were recorded. Before each exposure

voltage gradients were measured using a voltmeter with positive and negative probes spaced 1-

cm apart.

Pilot experiments were conducted to determine appropriate output voltages and exposure

durations. Six voltage gradients (2.9, 5.4, 8.2, 12.7, 16.3, 20.6 V/cm) with 5 replicates and

controls (n = 5) for a 20- and 30-second (sec) exposure duration were used. The procedures of

Nutile et al. (2013) for handling and exposing fish embryos to electricity were followed.

Embryos were exposed to electricity in PVC holding baskets. Holding baskets were 5-cm tall 2”

diameter PVC with mesh screen lining the bottom. There were approximately 26 holes near the

base of the PVC basket to allow electricity to flow into the basket. The outside of the basket was

lined with nylon mesh to minimize embryos escaping. Approximately 30 embryos were placed

24

in each basket just prior to exposure. Baskets were exposed individually. Prior to exposure,

approximately 5 embryos were removed from the basket and placed in a Petri dish labeled and

filled with water. These embryos were placed under a stereomicroscope (Nikon SMZ800) and

measured to the nearest 0.001 mm. Immediately following exposure the basket was returned to

the holding tank and mortality was assessed 24 hours post exposure. All embryos from each

basket (≈ 25 individuals) were observed under a microscope to determine whether each embryo

was dead. Any individuals that looked opaque or white in color were considered dead (Bohl et

al. 2010), but staff also looked for movement within the yolk sac and used light external probing

to look for a response to stimulus. The proportion of embryos from each basket that was dead

after 24 hours was calculated.

25

RESULTS

Objective 1: Determine northern pike seasonal movements, physical habitat, and water

quality parameters in Chelatna, Whiskey, and Hewitt lakes.

Radio-tag tracking occurred on 45 days during July–October of 2012, March 2013, and June–

October of 2013 (tag batteries were dead for 2014) with approximately 1,750 individual

detections recorded. In Whiskey and Hewitt lakes, northern pike were most often relocated

around the perimeter at depths < 10 ft. In Whiskey Lake, radio tagged pike used the southwest

perimeter most. In Hewitt Lake, radio-tagged pike used the south perimeter near the outlet most

(Figure 9). Use patterns cannot be used to make inferences about the larger population of pike

because most radio-tagged pike were originally captured in these areas rather than at random

locations; if anything, these data indicate that most pike have limited home ranges and high site

fidelity. Only 3 (2.5%) of the 119 radio-tagged pike were recorded as having moved between

Whiskey and Hewitt lakes. There was more movement between the southern end of Hewitt Lake

and the beginning of the creek system, with 10 pike being recorded in both Hewitt Lake and the

creek. A total of 450 recaptures of 378 PIT-tagged individuals were recorded, with some pike

being recaptured more than once. Only 6 PIT-tagged fish (1.6%) were recorded as having moved

between the 2 lakes. Movement between the lakes and the creek system was more common.

Limited geospatial vegetation data were collected during radio tracking in 2013 so inferences

about the association of relocated pike with specific vegetation are not possible. Vegetation was

noted for 194 pike relocations. Of these 194 relocations, presence of submerged vegetation was

noted at 97 (50%) relocations and presence of no vegetation was noted at 97 relocations. No

relocations noted presence of rooted floating leaved, nonrooted floating leaved, or emergent

vegetation. Vegetation was randomly sampled at 74 sites in Hewitt Lake and 61 sites in Whiskey

Lake in 2013. Vegetation was only documented at 21 (28%) sites in Hewitt Lake and 15 (25%)

sites in Whiskey Lake and vegetation type was dominated by submerged vegetation in both

lakes. Comparisons with pike relocations suggest that pike associations with submerged

vegetation were greater than expected by chance alone. The physical habitat where pike were

relocated varied little across seasons. The interquartile (25—75th) range of depth across June–

September in 2013 was 1–3 m. There were no significant differences in depth among months.

26

Figure 9: Locations of radio tagged pike.

Locations of radio tagged pike from telemetry surveys in Whiskey and Hewitt Lake systems.

Darker shades represent a higher density of relocations in that area.

The interquartile range of Secchi disk depth was 1–2.5 m across June–September in 2013; when

paired with depth, this indicates that pike were relocated in habitats that had high visibility.

Relative to other months, pike relocated in July occurred in habitats with greater Secchi depth

(2–4 m). Interquartile ranges of subsurface/maximum depth temperatures (°C) where pike were

relocated were 19.7–22.6/16.9–21.2 (June), 21.3–23.2/20.4–22.1 (July), 15.7–17.6/15.5–16.7

(August), and 12.3–13/12.3–12.9 (September). Interquartile ranges of subsurface/maximum

depth dissolved oxygen (mg/L) where pike were relocated were 10.3–11.3/10.5–12.2 (June),

10.4–10.8/10.6–11.25 (July), 10.9–11.4/10.8–11.3 (August), and 10.8–11.3/10.5–11.2

(September). Temperatures varied across seasons, but dissolved oxygen remained relatively

constant.

27

Physical habitat was also surveyed at defined sampling locations throughout each lake in June,

August, and September. These surveys represent habitat and water quality parameters at

locations used for gillnetting rather than for the lake as a whole. The majority of sampling

locations were near shore. The interquartile range of depths was 0.7–1.75 m and Secchi depth

was 0.6–1.5 m. Interquartile ranges of subsurface/maximum depth temperatures (°C) were 16.5–

19.3/7.5–17.3 (June), 17.8–19.2/13.7–19.1 (August), and 8.3–10.4/6.4–10.2 (September).

Interquartile ranges of dissolved oxygen (mg/L) were 11.5–12.6/11.5–13.6 (June), 10.3–

10.7/9.5–10.9 (August), and 11.4–11.8/7 –11.6 (September). When these available habitats are

compared to habitats where pike were relocated, the fish appear to select warmer habitats in

June, cooler habitats in August, and warmer habitats in September. There does not appear to be a

consistent pattern with dissolved oxygen; however, it is noted that temperature and dissolved

oxygen are often correlated.

Habitat and water quality parameters were also collected in Chelatna Lake, predominately along

the shore line and in shallow water areas where gillnetting of northern pike occurred. The

interquartile range of depths was 0.60–2.00 m. The interquartile range of Secchi depths was also

0.60–2.00 m. Vegetation was present at only 9.6% of the sampling locations with common water

moss (Fontinalis antipyretica) and whorled leaf watermilfoil (Myriophyllum verticillatum)

constituting the majority. Substrate consisted of sand/silt, gravel/cobble, and boulders (34%,

33%, and 33% respectively). Interquartile ranges of subsurface temperature (°C) in 2013 were

9.8–12.2 (June), 14.0–15.9 (August), and 7.3–8.3 (September) and in 2014 were 13.5–14.9 (July)

and 11.6–12.3 (August). The interquartile ranges of subsurface dissolved oxygen (mg/L) in 2013

were 9.8–10.44 (June), 9.81–10.08 (August), and 10.88–11.24 (September) and in 2014 were

10.46–10.90 (July) and 10.53–10.68 (August). Northern pike were most often captured in Pike’s

Pond (Appendix 1) where temperatures and dissolved oxygen were typically greater compared to

the remainder of the lake. Pike’s Pond is a shallow water (less than 1.5 m in depth) side slough

and constitutes the majority of the vegetated habitat in Chelatna Lake.


structure in Chelatna, Whiskey, and Hewitt lakes.

To estimate abundance, capture-mark-recapture techniques were used. All captured northern

pike > 250 mm were marked with a PIT tag in 2012 and 2013. A total of 1,365 northern pike

were PIT tagged in the Whiskey–Hewitt system in 2012 and 2013 (Table 1). In 2014, a total of

2,032 pike were harvested from the system with 299 (14.7%) having been previously tagged

(Table 1). Abundance estimates (95% CI) for pike > 250 mm are 1,046 (714–1,531) in Hewitt

Lake, 3,419 (2,569–4,550) in Whiskey Lake, and 3,496 (1,854–6,593) in the Whiskey–Hewitt

Creek outlet. Based on the estimates of 1,046 pike in Hewitt Lake (558 acres) and 3,419 pike in

Whiskey Lake (271 acres), the density of pike in this system is 1.9 pike per acre in Hewitt Lake

and 12.6 pike per acre in Whiskey Lake. Abundance estimates should be considered with low

28

confidence because of multiple assumption violations of a Whiskey–Hewitt closed system and

sampling regime, however they do provide a relative reference point for comparisons.

Table 1: PIT-tagged, recaptured and harvested northern pike in the Whiskey and Hewitt lakes system 2012–2014.

Dominant size classes varied by year in each lake and by age. Analysis of cleithra showed that

most fish were between 2 and 5 years old (y.o.) (Figure 10). In Hewitt Lake, large fish (500–700

mm) were most abundant in 2012 (Appendix 2). Based on age analyses, these pike were > 4 y.o.

The proportion of these large fish decreased in 2013 and 2014. In 2013, fish 350–450 mm (2–4

y.o.) were most abundant. In 2014, fish around 300 mm (2 y.o.) were most abundant. These 2014

data indicate that removal efforts missed larger fish (even though they were still theoretically in

the system), which have a disproportional importance to reproduction. Sampled Whiskey Lake

pike were smaller than Hewitt Lake pike. In 2014, 500 mm pike (3–6 y.o.) were most abundant.

In 2013, 300 mm (2 y.o.) and 400 mm (3 y.o.) pike were most abundant. In 2014, removal efforts

were most effective on 300–400 mm pike (Appendix 3). Whiskey Creek and Hewitt Creek pike

followed similar patterns as Whiskey Lake and Hewitt Lake, respectively. Importantly, 2014

removal efforts were not representative of the size structures observed in the Whiskey and

Hewitt lakes system during 2012 and 2013.

Whiskey Hewitt Whiskey/ Hewitt Creek Total

2012 Tagged 486 222 158 866

2012 Recap 48 33 12 93

2012 Harvest 65 27 6 98

2013 Tagged 255 103 141 499

2013 Recap 35 13 10 58

2013 Harvest 1 12 12 25

2014 No tag 1300 343 90 1733

2014 Recap 256 20 23 299"Tagged" refers to new cap tures that were PIT tagged . "Recap" is recap ture o f p revious ly tagged .

In 2014 all p ike were harves ted . "No tag" were cap tured without a PIT tag . "Recap" were harves ted ones with a PIT tag .

"Harves t" are p ike that either d ied during g ill net t ing o r workup

29

Figure 10: Length at age for Whiskey and Hewitt lakes, 2014.

Figure 11: Length at age for Chelatna Lake, 2014.

In Chelatna Lake the dominant size class reduced each year (Figure 12). In 2012, the dominant

size class for 2012 was 300 mm, in 2013 it was 225–250mm, and in 2014 it was 200 mm. In all 3

years, relatively few pike greater than 500 mm were captured in Chelatna Lake. Interestingly,

pike at Chelatna had the greatest weight at length and Whiskey had the lowest (Figure 13).

0

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1000 1200

Ag

e

Length (mm)

Whiskey and Hewitt 2014

0

1

2

3

4

5

6

0 100 200 300 400 500 600

Ag

e

Length (mm)

Chelatna 2014

30

Figure 12: Kernel density estimate of length (mm) for Chelatna Lake.

Figure 13: Polynomial representation of weights at length for pike harvested from Chelatna, Hewitt, and Whiskey

lakes 2012–2014.

31

Sex ratios varied by lake for pike harvested in 2014. Staff were not able to determine sex of all

pike, especially for pike less than 200 mm. Of the sexed northern pike, females were the

dominant sex in the Whiskey–Hewitt system with 61%, 69%, and 53% in Hewitt, Whiskey, and

the creek respectively (Figure 14). In Chelatna, the sex ratio was more evenly distributed with

49% females and 51% males.

Figure 14: Sex ratios of northern pike harvested in 2014.

“Creek” refers to northern pike harvested from the Whiskey–Hewitt creek system.

Objective 3: Investigate effective methods to mitigate loss of salmon production areas

through targeted northern pike harvesting.

Gillnet suppression efforts in the Whiskey–Hewitt complex were used to remove northern pike

in 2014. Crews removed 412 northern pike in Hewitt Lake, 1,697 northern pike in Whiskey

Lake, and 134 northern pike in the outlets. Catch per unit effort (CPUE) estimates for the

Whiskey–Hewitt system were greatest in 2012, even though the population size theoretically

remained the same until harvesting began in 2014 (Appendix 4). During the northern pike

harvest in 2014, Hewitt Lake had the greatest CPUE (Figure 15), but also had significantly fewer

total hours than Whiskey Lake. The CPUE decreased with increased fishing pressure as more

northern pike were removed. As fish are removed from the population there are fewer

individuals to be captured and catch rates are reduced.

32

Figure 15: Gillnetting CPUE for the Whiskey and Hewitt lakes system.

Multiple suppression methods were used to remove northern pike in 2012–2014 in Chelatna

Lake. Crews removed 667, 507 and 1,041 northern pike in 2012, 2013, and 2014 and removal

efforts were most effective on 2-year old pike (~ 180 – 250 mm ) that were < 1 kg. In 2012,

gillnets had a greater CPUE than fyke nets and hook and line. In 2013 and 2014, fyke nets had a

greater CPUE than gillnets and hook and line (Figure 16). Data from 2010 and 2011 were

obtained from a previous project with ADF&G and CIAA and indicate that 2010 had the highest

gillnetting CPUE for Chelatna Lake (Bill Glick, ADF&G unpublished data). Netting hours

increased each year from 2010 through 2014 at Chelatna Lake (Appendix 4) while catch rates

decreased.

Figure 16: Chelatna CPUE 2010–2014.

0

0.5

1

1.5

2

2.5

3

Whiskey Hewitt Creek

Pik

e p

er

ho

ur

Whiskey/Hewitt CPUE

2012

2013

2014

33

Stomach content analysis was conducted on harvested northern pike to determine the diet of

northern pike and their potential predation on salmonids. Northern pike in all lakes had a varied

diet, but were primarily piscivorous (Figure 17). Northern pike with salmon smolt or fry in their

stomachs often had between 1 and 5 individuals, but as many as 17 fry were recorded in the

stomach contents of a single northern pike (Figure 18). Salmon fry and smolt were not always

able to be determined to the species level. Of the 1,041 pike harvested from Chelatna in 2014, fry

were recorded in 334 (32%) and smolt were recorded in 123 (12%). Some northern pike had both

fry and smolt in their stomach and are therefore represented in both categories. In total 1,462 fry

and 184 smolt were found in northern pike stomachs.


passage and to prevent the creation of flooded vegetation conducive to northern pike.

The first survey was conducted during the peak of the sockeye migration (late July) each year to

maximize the number of salmon that were able to pass following notching. The second survey

each summer was to determine if notched dams had been repaired and required further notching,

or if additional dams had been built. If salmon were congregated at the base of the beaver dam,

they were often seen jumping and passing the dam immediately following notching. On most

streams the dams had not been repaired by the time of the second survey.

In 2012, the majority of the creeks surveyed had either no observed beaver dams or the dams

were determined to not be preventing fish passage and therefore notching was not required.

However; on Shell Creek there were 3 dams that required notching.

In 2013 one dam was notched on Three Mile Creek, 2 on Coal Creek Lake Creek, 3 on Kroto

Creek, 1 on the creek between Movie Lake and Trinity Lake, 1 on Shell Creek, and 2 on Trinity

Creek (Appendix 5).

In 2014 there was sufficient water flow on all creeks and no notching was required.

34

Figure 17: Stomach contents of northern pike in Whiskey, Hewitt, and Chelatna lakes.

Pike frequently had more than one category in their stomach contents and a single

individual may be recorded in more than one category. Partial fish

were too digested to identify to the species level. In Chelatna partial fish were predominately

salmonids and in Whiskey–Hewitt they were sticklebacks. Stomach contents were taken from

the Whiskey Hewitt system in only 2014.

34

35

Figure 18: Number of smolt and fry recorded in northern pike stomachs.

This figure displays how many pike were recorded with

various numbers of smolt and fry in their stomachs.

35

36

Objective 5: Develop and assess the ability of NEPTUN barrier technology to influence

pike movement.

Bozeman (from Sepulveda et al. in press)

Eighty juvenile trout and 40 adult trout (all adult trout exposed twice during experiments) were

exposed to the barrier, but 3 juvenile trout (4%) and 7 adult trout (9%) never approached the

barrier’s electric field; 3 of the adult trout were control fish. These 10 trout were excluded from

analyses.

Fish passage varied between pulse widths (F3,145 = 7.48, P <0.001) but not between voltages

(F3,145 = 2.53, P = 0.06). Results of post hoc tests suggested that passage differed between

control levels (0 ms) and 0.7 ms (P < 0.01) but not between control and 0.4 ms (P = 0.07) or 0.1

ms (P = 0.8). Control voltage levels did not differ from 0.24 V cm-1

(P = 0.31), 0.33 V cm-1

(P =

0.06) or 0.44 V cm-1

(P = 0.09). Five of 8 juvenile trout (63%) and 3 of 5 adult trout (60%)

swam through the entire length of the barrier when the barrier was turned off (control).

Top ranked models were used to compare fish passage to barrier settings and fish size related

juvenile and adult trout passage to pulse width. Based on the top ranking model, the probability

of juvenile and adult trout passing the barrier at 0.1 ms was 45%, and odds of passing at 0.1 ms

were 2.0 times higher than at 0.4 ms (29% probability of passing) and 6.7 times higher than at

0.7 ms (11% probability of passing). There was no voltage × pulse width setting that inhibited

100% of adult trout while allowing > 50% of juvenile trout to pass (Figure 19). The highest

percentage of juvenile trout passing (63%) was at the lowest barrier setting (0.24 ± 0.01 V cm-1

,

0.1 ms); where 50% of adult trout also passed. All adult trout that were exposed to 0.33 ± 0.02 V

cm-1

and 0.4 ms (n = 7) and 0.32 ± 0.01 V cm-1

and 0.7 ms (n = 6) did not pass the barrier, and

only 13% of juvenile trout (n = 2) exposed to those settings passed the barrier.

Deflection rates differed between 0.1 ms and 0.4 ms (β = 0.14, t = 2.7, P < 0.01) and 0.7 ms (β =

0.13, t = 2.5, P < 0.05), and by FL (β = -0.23, t = -2.8, P < 0.01) but not between 0.24 V cm-1

and 0.33 V cm-1 (β = -0.02, t = -0.3, P = 0.76) or 0.44 V cm-1 (β = 0.06, t = 1.27, P = 0.21)

(Figure 14). Ninety-eight percent of juvenile trout (n=70) made attempts to pass but were

deflected at least one time and 84% of adult trout made attempts to pass but were deflected at

least one time (n=57). Results of GLM comparing fish passage to deflection rates and fork length

suggest there was an negative effect of deflection rates and fork length (interaction) on fish

passage (β = -8.4, z = -2.33, P < 0.05). Larger fish and fish that were deflected more by the

barrier were less likely to pass the barrier.

37

Figure 19: Passage rate of rainbow trout with NETPUN barrier.

One juvenile trout (1%) and 9 adult trout (16%) demonstrated loss of equilibrium 0.5 h after

exposure. No trout died 0.5 h or 192 h post-exposure. External bruising was observed in 5

juvenile trout (7%) and 18 adult trout (25%). The sample size of bruised juvenile trout was too

small to statistically evaluate. The number of adult trout bruised did not differ across voltages

(F2,63 = 1.22, P = 0.3), pulse widths (F2,60 = 0.72, P = 0.49), passage (F1,64 = 3.88, P = 0.05), or

the number of deflections (F1,62 = 1.53, P = 0.22). There was no relationship between adult trout

bruising on day 8 (37% of trout, n = 7) with voltage (F3,12 = 1.05, P = 0.41), pulse width (F2,13 =

1.98, P = 0.18), passing (F1,15 = 0.15, P = 0.71), or number of deflections (F1,15 = 0.03, P = 0.87)

on day 1 of experiments.

No juvenile trout died 0.5 h or 192 h post-exposure. Five trout (7%) sustained external bruising

at 0.34 ± 0.01 V cm-1and 0.1 ms (n = 1), 0.34 ± 0.01 V cm-1and 0.4 ms (n = 1), 0.45 ± 0.01 V

cm-1 and 0.1 ms (n = 1), and 0.45 ± 0.01 V cm-1and 1.0 ms (n = 2). External bruising appeared

to have no long term negative effects on the survival of trout.

Whiskey

A total of 250 northern pike were used in this study over 25 trials. The average length of

northern pike used in this study was 448 mm (±84 mm). There were 330 total observed

38

interactions with the NEPTUN barrier system over the 25 trials. On average 30.4% (±10%) of

northern pike passed the barrier, 63.7% (±13.1%) were repelled, 4% (±8%) were trapped, and

2% (±4%) were stunned in each trial (Figure 20). Voltages in the barrier were less than 0.40 V

cm -1

(peak voltage, not the average of one cycle) (Appendix 6). No northern pike died following

exposure to the barrier system; however, a few lost equilibrium and were caught and consumed

by river otters. River otters appeared to not be effected by the NEPTUN barrier.

Figure 20: Northern pike responses to interaction with NEPTUN barrier.

Objective 6: Assess the utility of electricity in eradicating northern pike embryos and

larvae in lab and spawning environments.

Survival in control embryos ranged from 60–83%, but 100% mortality was not achieved at any

voltage gradients at 20-sec exposure durations (Appendix 9) but 100% mortality was achieved at

30-sec exposure at 16.3 V/cm. Embryo mortality was related to voltage gradient (one-way

ANOVA; F5, 16 = 5.67, P = 0.003) such that mortality increased with increasing voltage gradients

when exposed to electricity for 20 seconds. Mortality was also higher with increasing voltage

gradients for embryos exposed to electricity for 30 sec, however, mortality was higher at lower

voltages (≥ 5.4 V/cm) compared to 20-s exposure (Appendix 10).

Passed30%

Repelled64%

Trapped4%

Stunned2%

Pike Responses

39

DISSCUSSION

Movement data indicated that northern pike were most commonly found in the shallow water

habitat along the perimeter of Whiskey and Hewitt lakes, consistent with previous studies (Diana

et al. 1977). The majority of Whiskey Lake has optimal northern pike habitat, while only

portions of Hewitt Lake have good habitat. In Chelatna Lake, habitat appears to be a limiting

factor and northern pike were most frequently caught in a shallow water side slough with denser

vegetation. Habitat usage from this study is similar to previous research in that northern pike are

associated with aquatic vegetation of littoral and shoreline habitat (Bry 1996, Grimm and Klinge

1996, Pierce 2012). Comparisons of northern pike relocations and vegetation sampling indicate

northern pike are associated with submerged vegetation greater than what could be expected by

chance alone.

Northern pike are capable of long distance movements, with some individuals traveling up to 4

km in a single day (Diana 1980). Movement data from this project indicated relatively low rates

of movement between Whiskey and Hewitt lakes for radio-tagged and PIT-tagged northern pike

with 2.5% and 1.6% respectively being recorded moving between lakes. These movement data

are important for future suppression efforts because recolonization rates for these lakes may be

relatively low. However, even at relatively low movement rates northern pike are prolific

spawners (Pierce 2012) and capable of rapid population expansion. This study only focused on

movement patterns of northern pike within the system and does not provide an indication of the

influx rate of northern pike from outside the system. Additionally, movement rates between these

2 lakes may change once suppression efforts are in effect and niches are opened.

Northern pike appear to select warmer habitats in June, cooler habitats in August, and warmer

habitats in September. There does not appear to be a consistent pattern with dissolved oxygen;

however, it was noted that temperature and dissolved oxygen are often correlated. These findings

are consistent with previous studies. Northern pike are tolerant of a wide range of dissolved

oxygen levels, but are considered a cool water fish that thrives best in waters less than 28˚C

(Pierce 2012). Northern pike were often located in areas with relatively high visibility, which is

not surprising since they are sight predators.

The abundance estimates in Whiskey and Hewitt lakes should be considered with low confidence

due to assumption violations in capture-mark-recapture methods, but do offer a relative reference

point of the populations. Abundance estimates (95% CI) for northern pike > 250 mm are 1,046

(714–1,531) in Hewitt Lake, 3,419 (2,569–4,550) in Whiskey Lake, and 3,496 (1,854–6,593) in

the Whiskey–Hewitt Creek outlet. Whiskey Lake has approximately one-half the surface area of

Hewitt Lake, but the pike population is estimated to be nearly 3 times as large. Population

density was estimated at 1.9 and 12.6 pike per acre for Hewitt and Whiskey lakes respectively.

These estimates indicate that habitat availability is a driving factor in northern pike populations.

40

Whiskey Lake is predominately vegetated, shallow water (<8 m) that is very conducive to

optimal northern pike habitat. Shallow lakes with large amounts of littoral habitat typically have

higher densities of smaller northern pike. Deeper cooler lakes usually have low densities of

larger northern pike (Pierce 2012). Hewitt is a deeper lake (up to 35m) with limited available

northern pike habitat. Abundance estimates were not performed at Chelatna Lake, but gillnet

CPUE indicated that the population of northern pike (>250 mm) is decreasing and currently low.

This is the result of multiple years of northern pike suppression, but the initial population density

was probably relatively low due to limited habitat.

Northern pike size varied by lake with dominant size class in Whiskey Lake 300 to 500 mm, in

Hewitt 300 to 600 mm, and in Chelatna less than 400 mm. Representative size distribution in

Whiskey and Hewitt lakes is skewed because the majority of the fish were captured in gillnets

with 1-inch bar mess and these nets predominately captured fish greater than 250 mm. Due to

assumption violations in 2012 and 2013, population growth rate could not be estimated for

Whiskey and Hewitt lakes so the removal effort required to reduce northern pike population

growth rates cannot be concluded. Comparisons of northern pike removed in 2014 relative to

2012–2013 estimates indicate that gillnet efforts removed much less than 50% of the northern

pike population >250 mm. Importantly, 2014 removal efforts were not representative of the size

structures observed in 2012 and 2013, even though sampling sites remained consistent and pike

should have theoretically remained in the system.

For Chelatna Lake, it is important to note the dominant size class decreased each year and in all

years relatively few large northern pike were captured. Fyke hoop nets became the most effective

means of capturing pike, especially for less than 200 mm fish. Smaller northern pike were often

gilled or had their teeth entangled in the leads of the first 2 compartments of the net. These fish

were primarily 1 year olds and later in the summer young-of-year were captured as well. Fyke

hoops nets may be an important means to capture smaller northern pike that are able to avoid

gillnets, but rarely were northern pike less than ~125 mm captured. Removal of small northern

pike is essential to suppression efforts because they have been shown to be the primary

consumers of juvenile salmonids (Sepulveda et al. 2012). The catching of 1-year-old and young-

of-year pike over multiple years indicates that gillnetting alone is not sufficiently removing all of

the spawning population.

Northern pike weight at length was greatest for Chelatna Lake, with Hewitt second, and Whiskey

last. This trend is likely a result of population density and competition for limited available food.

As noted before, shallow lakes with lots of vegetation typically have higher densities of smaller

northern pike whereas deeper lakes have lower densities (Pierce 2012). Stomach content analysis

showed that salmon consumption was highest in Chelatna Lake, but this is partially due the

availability of juvenile salmon for consumption. At Chelatna Lake the smolt enumeration

estimate was 278,129 for 2010, 336,299 for 2011, and 397,917 for 2012 (CIAA Staff 2013).

41

Smolt production at Whiskey Lake was 15,983 in 2012, 2,986 in 2013, and 1,537 in 2014

(Smukall 2015). Northern pike have been responsible for the decline of native fish species in

other system (Sepulveda et al. 2012) and this may be occurring at Whiskey Lake. Stomach

contents collected at Whiskey Lake in 2014 are most likely not representative of the past when

juvenile salmon numbers were higher. Once salmonids have been depleted, pike will shift their

diet to other available food sources (Sepulveda et al. 2012) and in Whiskey Lake this other food

source appears to be predominately sticklebacks.

Digestion rate is dependent on many factors, including temperature, food quantity, and food

quality, but northern pike require approximately 20 hours for 50% digestion of stomach contents

and 50 hours for 100% digestion at 18 to 23 degrees Celsius (Seaburg and Moyle 1964).

Identification of stomach contents is more difficult as digestion progresses, meaning the stomach

contents observed in this study are likely to have been consumed within 1–2 days prior to

harvest. Multiple factors will influences the feeding rate of pike, including temperature, time of

year, and predation risk, but data from stomach contents can be used to give an indication to the

magnitude of impact northern pike can have on salmon populations. Assuming those northern

pike had not been harvested from Chelatna Lake, as a group they could have consumed

approximately 1,500 juvenile salmonids every 2 days. The open water season at Chelatna Lake is

approximately 5 months, or 150 days. Over that time those northern pike could have consumed

112,500 juvenile salmon. This figure does not include the other unknown number of northern

pike in Chelatna Lake or the consumption during the winter months. This estimate should be

taken with low confidence and is potentially conservative, but this underscores the impact

northern pike can have on native salmonids.

Gillnetting typically only captures larger northern pike and there is the possibility of reinvasion

from other connected water bodies, therefore additional technology is required to assist with

suppression efforts. Eradication with rotenone has been proposed for some water bodies that

historically produced large numbers of salmon but are now dominated by northern pike with few

other native species remaining. Rotenone is an indiscriminate fish killer and would require the

capturing and holding of native fish at a secondary water body or hatchery until they could be

reintroduced, allowing native fish to naturally recruit to the water body, or stocking of the water

body with native fish species from other systems. In order for long-term restoration efforts to be

successful, there is a need to ensure that northern pike will not be able to easily reinvade these

water bodies by moving back in from connected systems.

The effect of the NEPTUN vertical pulsed direct current barrier was first tested to ensure

minimal impact on native fish species. Rainbow trout mortality and physical condition across the

range of barrier settings tested was minimal. Therefore, in specific management applications

electric barriers may function as a tool to inhibit target species movements without causing lethal

harm to nontarget fish. This study provides information that may aid managers in selecting

42

appropriate voltage gradients and pulse widths for application in areas where vagile, nontarget

species reside, like smolting salmonids. It was hypothesized the NEPTUN vertical pulsed-direct-

current electrical barrier system could be used to successfully block the movement of northern

pike and guide them into “live box” holding areas. However, when tested in Whiskey Creek only

64% of the pike were repelled, while 30% were able to pass. The system only successfully

guided 4% of pike into the holding area and 2% were stunned. A 30% passage rate of northern

pike is too high to protect systems from pike invasion. Northern pike are prolific spawners and

even a few individuals passing into a system can lead to rapid population increases.

The settings used for the northern pike portion of the study were designed to produce a

maximum voltage (0.4 V cm -1

) in the water column less than what had been previously tested

with juvenile salmonids (max of 0.45 V cm -1

). It was determined that no mortality occurred of

juvenile salmonids and that injury was rare at this voltage level. However, barrier avoidance was

observed for juvenile rainbow trout (Adam Sepulveda, USGS unpublished data). Barrier

avoidance by emigrating juvenile salmonids needs to be considered when determining where to

place a barrier system. One option to overcome barrier avoidance is to place the barrier system in

a section on the creek with relatively swift current that would help to move juveniles through the

barrier. Testing with rainbow trout was conducted in a laboratory setting with no flow and

juveniles were capable of swimming away from the barrier. Also smolting salmon emigrating

from the lake may show more instinctual drive for downstream movement and may be more

willing to pass through the barrier than juvenile rainbow trout in the laboratory setting.

The NEPTUN system has been used to successfully block 100% of sea lamprey movement, but

the voltage in the water column was far greater than in our current study, 1.8 V cm -1

compared

to 0.4 V cm -1

(Johnson et al. 2014). However, the barrier system did not significantly increase

the numbers of sea lampreys guided into holding areas (Johnson et al. 2014). In addition, these

settings blocked the movement of native rainbow trout and white suckers. The findings presented

here, in addition to those of Johnson et al. (2014), indicate that the NEPTUN barrier in its current

configuration may be better suited for blocking fish movement. However, refining the

configuration of the barrier and trap designs may increase the success of capture in holding areas.

Once northern pike entered the electrical field, their movements were often erratic and

unpredictable bursts. It often appeared to observers that passing of the barrier was a matter of

luck for northern pike. They did not swim in a straight line through the barrier but rather in

unpredictable paths until they were out of the electrical field. This erratic and unpredictable

swimming made it too difficult to determine the best placement for traps in the stream. One

suggestion would be to have traps with funneling systems that cover a large area of the stream to

increase the likelihood of northern pike capture.

Using the barrier system at a higher voltage gradient may also prevent northern pike from

swimming too far into the barrier system before they feel the effects. In this study it was

43

observed that northern pike made it past the first row of electrodes before they reacted. A higher

voltage may result in northern pike reacting sooner and more likely to turn around. It is

important to note that the voltage observed in the water column is a result of many factors

including electrode spacing, number of electrodes, water conductivity, water depth, and

substrate. Therefore replicating the NEPTUN settings from this study at another water body is

not likely to result in the same voltage in the water column. It is important to test the voltage at

each installation and modify the NEPTUN system configuration in order to achieve the desired

voltage.

Exposure to electricity may be an effective means for suppressing survival of northern pike

embryos but 100% mortality was only achieved with 30-second exposure at 16.3 V/cm.

However, achieving complete coverage of potential spawning habitat in many lake systems may

be difficult. The remoteness and vast network of side sloughs and swampy habitat in the Sustina

River basin make it unlikely to achieve 100% coverage of exposure to electricity. Northern pike

are prolific spawners—even low survival rates of reproductive success may be enough to sustain

a population. This technology may be effective at reducing northern pike numbers by

concentrating on targeted habitats in conjunction with other suppression efforts.

44


45

CONCLUSION

Invasive northern pike have become well established in many systems within the Susitna River

drainage and their impact on native fish species has been well documented. Consistent with other

studies, the findings of this study show that northern pike are capable of consuming large

numbers of juvenile salmonids but can change their diet when their preferred prey is not

available.

It appears that the limiting factor of northern pike population in Cheltna Lake is available habitat.

Perhaps this is why the population there is not at high enough densities to show noticeable

impacts to the salmon population. However, even at a low density the northern pike in Chelatna

Lake are consuming a large number of juvenile salmon. Northern pike movement between

Whiskey and Hewitt lakes was relatively low, and this has important management implications

for suppression efforts. Recolonization rates may be low, but even at low numbers northern pike

have the potential to harm native fish species. Additionally, when northern pike first move into a

system, or return after being eliminated, they are likely to experience rapid population growth. It

is therefore important to prevent recolonization.

At the tested settings, the NEPTUN barrier did not consistently prevent northern pike passage.

However, these settings were designed to ensure minimal negative impacts to native fish species

and tests at higher settings should be conducted. The impact of the NEPTUN barrier on returning

adult salmon should also be explored.

Gillnets had some success at catching larger northern pike, but potentially not enough to

meaningfully reduce the population in Whiskey Lake. Fyke hoop nets were successful at

catching smaller northern pike, but only once the fish reached ~125 mm. A combination of

intensive field work and new technology is likely required for northern pike suppression to be

successful.

46


47

REFERENCES

Alaska Department of Fish and Game. 2015. Invasive Pike in Southcentral Alaska.

www.adfg.alaska.gov. Accessed June 11, 2015.

Applegate, V.C., Smith, B.R., Nielsen, W.L. 1952. Use of electricity in the control of sea

lampreys. U.S. Fish and Wildlife Service Special Science Report Fisheries, 92. pp.52.

Baker, S., (1928). Fish screen in irrigating ditches. Transactions of American Fisheries Society.

58, 80-82.

Bohl, R.J., Henry, T.B. and Strange, R.J. 2010. Electroshock‐induced mortality in freshwater

fish embryos increases with embryo diameter: a model based on results from 10

species. Journal of Fish Biology, 76(4): 975–986.

Bry, C. 1996. Role of vegetation in the life cycle of pike. Pike Biology and Exploitation.

Chapman and Hall, London.

CIAA staff. 2013. Chelatna Lake Sockeye Salmon Smolt Data Report 2012. Cook Inlet

Aquaculture Association.

Diana, J.S. 1980. Diel activity pattern and swimming speeds of northern pike (Esox lucius) in

Lac. Ste. Anne, Alberta. Canadian Journal of Fisheries and Aquatic Sciences 37: 1454–

1458.

Diana, J.S., Mackey, W.C., and Ehrman, M. 1977. Movements and habitat preferences of

northern pike (Esox lucius) in Lac. Ste. Anne, Alberta. Transactions of the American

Fisheries Society 106:560-565.

Erkkila, L.F., Smith, B.R., McLain, A.L. 1956. Sea lamprey control on the Great Lakes 1953 and

1954. U.S. Fish and Wildlife Service Special Science Report Fisheries. 175.

Grimm, M.P. and Klinge, M. 1996. Pike and some aspects of its dependence on vegetation. Pike

Biology and Exploitation. Chapman and Hall, London.

Hassler, T.J. 1982. Effect of temperature on survival of Northern pike embryos and yolk-sac

larvae. The Progressive Fish-Culturist, 44(4): 174–178.

Johnson, Nicholas; Thompson, Henry; Holbrook, Christopher; and Tix, John. 2014. Blocking

and guiding adult sea lamprey with pulsed direct current from vertical electrodes. USGS

Staff – Published Research. Paper 828.

Lee, D. 2001. Northern Pike Control at Lake Davis, California. American Fisheries Society. 55–

61.

http://www.adfg.alaska.gov/

48

McLain, A.L. 1957. The control of the upstream movement of fish with pulsed direct current.

Transactions of American Fisheries Society. 86. 269–284.

Mecozzi, M. 1989. Northern pike (Esox lucius). Wisconsin Department of Natural Resources,

Bureau of Fisheries Management. Technical Report, p. 1–6.

Morrow, J.E. 1980. The freshwater fishes of Alaska. Alaska Northwest Publishing Company.

Anchorage, Alaska. 248 pp.

Munro, A.R., and E.C. Volk. 2014. Summary of Pacific salmon escapement goals in Alaska with

a review of escapements from 2005 to 2013. Alaska Department of Fish and Game,

Fishery Manuscript Series No. 14-01, Anchorage.

Nutile, S., Amberg, J.J. and Goforth, R.R. 2013. Evaluating the effects of electricity on fish

embryos as a potential strategy for controlling invasive cyprinids. Transactions of the

American Fisheries Society, 142(1): 1–9.

Patankar, R., Von Hippel, F. and Bell, M. 2006. Extinction of a weakly armoured threespine

stickleback (Gasterosteus aculeatus) population in Prator Lake, Alaska. Ecology of

Freshwater Fish 15: 482-487.

Pierce, R.B. 2012. Northern pike ecology, conservation, and management history. Minnesota

Department of Natural Resources. University of Minnesota Press. Minneapolis / London

Raat, A. J. P. 1988. Synopsis of biological data on the Northern pike Esox lucius Linnaeus, 1758.

Food & Agriculture Organization of the United Nations (FAO), FAO Fisheries Synopsis

No. 30 Rev. 2, Nieuwegein, Netherlands. ISBN 92-5-1023656-4.

Reynolds, J.B., Kolz, A.L., 2012. Electrofishing. In: Zale, A.V., Parrish, D.L., Sutton, T.M.

(Eds.), Fisheries Techniques. 3rd

ed. American Fisheries Society, Bethesda, MD. 305–

361.

Rutz, D. 1999. Movements, food availability and stomach contents of northern pike in selected

Susitna River drainages, 1996–1997. Alaska Department of Fish and Game, Fishery Data

Series. Anchorage, 1-68.

Rutz, D. 2014. Alexander Creek Northern Pike Suppression. Alaska Department of Fish and

Game. American Fisheries Society Alaska Chapter Presentation. October 2014.

Seaburg, K.G. and Moyle J.B. 1964. Feeding habits, digestive rates, and growth of some

Minnesota warmwater fishes. Transactions of the American Fisheries Society, 93(3):

269–285.

Sepulveda, A.J., Layhee, M., Shaw, A., Smukall, M., Kappenman, K., and Reyes, A. (in press).

Effects of electric barrier on passage and physical condition of juvenile and adult rainbow

trout.

49

Sepulveda, A.J., Rutz, D.S., Ivey, S.S., Dunker, K.J. and Gross, J.A. 2013. Introduced northern

pike predation on salmonids in southcentral Alaska. Ecology of Freshwater Fish, 22(2):

268–279.

Shields, P., and A. Dupuis. 2015. Upper Cook Inlet commercial fisheries annual management

report, 2014. Alaska Department of Fish and Game, Fishery Management Report No. 15-

20, Anchorage.

Smukall, M.J. (2015). Whiskey Lake Salmon Smolt Progress Report 2014. Cook Inlet


Spafard, M.A., and J.A. Edmundson. 2000. A Morphometric Atlas of Alaskan Lakes: Cook Inlet,

Prince William Sound, and Bristol Bay Areas. Alaska Department of Fish and Game

Regional Information Report. 2A00–23: 24.

Weber, Nathan (2010). Hewitt Lake Sockeye Salmon Final Report 2006–2007. Cook Inlet


Weber, Nathan (2011). Whiskey Lake Sockeye Salmon Data Report 2010. Cook Inlet


50


51

APPENDICES

52

Appendix 1: Southern end of Chelatna Lake and “Pike’s Pond”

53

Appendix 2: Kernel density estimate of length (mm) for Hewitt Lake

54

Appendix 3: Kernel density estimate of length (mm) for Whiskey Lake.

Appendix 4: Gillnet hours by lake and year.

55

Appendix 5: Map of beaver dam notching and surveys.

56

Appendix 6: Voltage gradient of Whiskey NEPTUN barrier.

The intensity of the NEPTUN vertical electric barrier field at Whiskey Creek measured in V cm -

1(peak voltage, not the average of one cycle). Blue is least intensity and red is highest

intensity. Brown areas are stream bank. Green areas are faraday cage live boxes with no

electrical field. Each cell represents a 1m by 1m section of the creek.

0 0

0 0 0.02 0.02

0.1 0.1 0.04 0.02 0

0.2 0.2 0.18 0.04 0 0.02 0 Creek Bank

0.2 0.1 0.2 0.22 0 0.04 0 0

0.1 0.2 0.1 0.2 0.2 0.1 0 0 0

0.2 0.1 0.2 0.2 0.2 0.1 0 0 0

Live Box 0.02 0.18 0.1 0.2 0.2 0.2 0.1 0 0 0.02

0.06 0.2 0.2 0.14 0.2 0.2 0.1 0 0.1

0.02 0.04 0.1 0.2 0.3 0.3 0.1 0 Live Box

0.02 0 0.06 0.2 0.3 0.3 0.1 0

0 0.04 0.2 0.2 0.2 0.3 0.4

Creek 0.02 0 0.1 0.2 0.2 0.1 0.38 0.38

Bank 0 0 0.2 0.2 0.1 0.4 0.18

Flow 0 0 0 0.2 0.2 0.18 0.1 0.1

0 0 0 0.18 0.18 0.2 0.1

0 0 0 0.04 0.2 0.2 0.2

0 0.02 0.02 0.02 0.2

0.02 0.4 0.1

0.02 0

57

Appendix 7: Pike reactions to NEPTUN barrier.

Appendix 8: Responses of pike to NEPTUN barrier as percentage.

Trial # Pass Repel Trap Stun

1 2 5 0 0

2 2 1 2 0

3 4 9 0 0

4 2 5 0 1

5 4 5 0 0

6 6 8 0 0

7 5 14 0 3

8 2 4 0 0

9 4 12 1 0

10 4 8 1 0

11 1 9 1 0

12 3 14 1 0

13 5 11 0 0

14 3 11 0 0

15 4 8 0 0

16 10 8 1 1

17 3 5 0 0

18 2 12 2 0

19 6 15 2 0

20 3 5 0 0

21 1 2 0 0

22 3 9 0 0

23 3 10 0 1

24 6 8 1 0

25 8 9 0 1

Total 96 207 12 7

% 29.7 64.6 3.6 2.1

Trial # Pass Repel Trap Stun

1 0.29 0.71 0.00 0.00

2 0.40 0.20 0.40 0.00

3 0.31 0.69 0.00 0.00

4 0.25 0.63 0.00 0.13

5 0.44 0.56 0.00 0.00

6 0.43 0.57 0.00 0.00

7 0.23 0.64 0.00 0.14

8 0.33 0.67 0.00 0.00

9 0.24 0.71 0.06 0.00

10 0.31 0.62 0.08 0.00

11 0.09 0.82 0.09 0.00

12 0.17 0.78 0.06 0.00

13 0.31 0.69 0.00 0.00

14 0.21 0.79 0.00 0.00

15 0.33 0.67 0.00 0.00

16 0.50 0.40 0.05 0.05

17 0.38 0.63 0.00 0.00

18 0.13 0.75 0.13 0.00

19 0.26 0.65 0.09 0.00

20 0.38 0.63 0.00 0.00

21 0.33 0.67 0.00 0.00

22 0.25 0.75 0.00 0.00

23 0.21 0.71 0.00 0.07

24 0.40 0.53 0.07 0.00

25 0.44 0.50 0.00 0.06

Average 0.30 0.64 0.04 0.02

Std Dev 0.10 0.13 0.08 0.04

58

Appendix 9: Pike embryo response to 20-sec direct current electroshocking.

20-sec exposure

Voltage gradient (V/cm)

0 2.9 5.4 8.2 12.7 16.3 20.6

Pro

po

rtio

n d

ea

d

0.0

0.2

0.4

0.6

0.8

1.0

Proportion pike embryos that were dead (24-hours after exposure) after

exposure to straight DC at a specific voltage gradient (V/cm) for 20 seconds.

59

Appendix 10: Pike embryo response to 30-sec direct current electroshocking.

30-sec exposure

Voltage gradient (V/cm)

2.9 5.4 12.7 16.3 20.6

Pro

po

rtio

n d

ea

d

0.0

0.2

0.4

0.6

0.8

1.0

Proportion of pike embryos that were dead (24-hours after exposure) after

exposure to straight DC at a specific voltage gradient (V/cm) for 30 seconds.

Documents

Northern Pike Investigations Final Report (2012 2014)