Research on Effects of Research on Effects of ElectrofishingElectrofishing

USFWS proposal: USFWS proposal: Effect of Electroshocking on Effect of Electroshocking on Native Southeastern Fishes with Emphasis on Species Native Southeastern Fishes with Emphasis on Species Protected under the Endangered Species ActProtected under the Endangered Species Act J.R. Shute, P. Rakes (Conservation Fisheries Inc.)J.R. Shute, P. Rakes (Conservation Fisheries Inc.)

Support for graduate research assistant (M.S.) to Support for graduate research assistant (M.S.) to begin fall 2006 (Dept FWF, UTK)begin fall 2006 (Dept FWF, UTK) Project objectivesProject objectives Additional fundingAdditional funding

Ted Henry, Adjunct Assistant ProfessorDept of Forestry, Wildlife, and Fisheries University of Tennessee, Knoxville, TN

Overall Objectives for Overall Objectives for Electrofishing Injury Electrofishing Injury

ResearchResearch Consider effect of different electric field Consider effect of different electric field

types (e.g., DC PDC) and investigate:types (e.g., DC PDC) and investigate: Survival of embryosSurvival of embryos Survival of vulnerable older life stagesSurvival of vulnerable older life stages Sub-lethal injury to tissuesSub-lethal injury to tissues

Consider T&E species or surrogatesConsider T&E species or surrogates Darters, madtoms, and shiners Darters, madtoms, and shiners

Electroshocking and Fish Early Life Stages

- Early life stages not targets of electrofishing

- Exposed during sampling for target fish

- Electrofishing during spawning season

- Effects of electrofishing on early life stages?

Previous Previous Electrofishing Injury Electrofishing Injury

ResearchResearch Projected funded by the USFWS through the Projected funded by the USFWS through the

Fisheries Management Section of AFSFisheries Management Section of AFS Examined effects of electrofishing in early life stages of Examined effects of electrofishing in early life stages of

warmwater fish (focused mostly on sportfish)warmwater fish (focused mostly on sportfish) Laboratory based research with field validationLaboratory based research with field validation Results indicate that investigations on effects on T&E Results indicate that investigations on effects on T&E

species are necessaryspecies are necessary

30 cm

Modified electrofishing pulse box

Oscilloscope

Aluminum plate electrodeshomogeneous electric field

Model of exposure chamber

Research Methods

• Channel catfish embryos in exposure chambers• Chambers had flow-through water exchange

Survival of Largemouth Bass Survival of Largemouth Bass Embryos after Exposure to 8 V/cmEmbryos after Exposure to 8 V/cm

0

20

40

60

80

100

0 5 10 15 20 25 30 35 40 45 50

Sur

viva

l (%

)

Time (h) postfertilization when shocking occurred

DC 60 120

a

a

b

Control

(survival 83%)

Hatching 48 h

Similar results for bluegill embryos

25 mm channel catfish

Age-related Mortality of Age-related Mortality of Largemouth BassLargemouth Bass

0 10 20 30 40 50 60 70 80 90

Mo

rta

lity

(%)

Age (d)

Predicted mortality 2 V/cm

Observed mortality 2 V/cm

Predicted mortality 4 V/cm

Observed mortality 4 V/cm

100

80

60

40

20

0

60-Hz PDC

cm

Electroshock-Induced Mortality of Electroshock-Induced Mortality of Newly Transformed Juvenile FishNewly Transformed Juvenile Fish

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16Voltage gradient (V/cm)

Mo

rta

lity

(%)

60-Hz PDC for 20 s

Channel catfish

Nile tilapia

Rainbow trout

Blackbandeddarter*

Largemouthbass

*adult

Grossly Visible InjuriesGrossly Visible Injuries

SpeciesSpecies Number Number shockedshocked

Number Number injuredinjured

control fishcontrol fish 138138 00

channel catfishchannel catfish 233233 7 (4 dead)7 (4 dead)

rainbow troutrainbow trout 302302 1010

striped bassstriped bass 6868 11

largemouth basslargemouth bass 324324 11

bluegillbluegill 311311 33

Nile tilapiaNile tilapia 147147 44

channel catfishanterior tailsagittal section

control

electroshocked20 s, 4 V/cm, 60-Hz PDC

spinal cordspinal cord

dorsal aorta

vertebravertebra

notochord

compressed compressed vertebravertebra

bluegill anterior tail sagittal section

electroshocked 5 s, 8 V/cm, 60-Hz PDC

Fractured vertebra (arrow) and hemorrhage (H)

H live fish had no indications of injury

Rainbow trout anterior tail sagittal section

electroshocked 20 s, 4 V/cm, 30-Hz PDC

Notochord hernia protruding between vertebrae

spinal cordspinal cord notochord notochord herniahernia

vertebraevertebrae

live fish had paralysis of the tail and posterior trunk

Nile tilapia anterior tail sagittal section

electroshocked 20 s, 16 V/cm, 60-Hz PDC

Necrotic Necrotic muscle muscle (arrows)(arrows)

live fish had uncoordinated swimming

necrotic muscle also found in control fish: 1 largemouth bass and 1 bluegill

Histopathology of Clinically Histopathology of Clinically Normal Fish 1 Hour After Normal Fish 1 Hour After

ElectroshockElectroshockLesionsLesions

channel channel catfishcatfish4 V/cm4 V/cm

bluegillbluegill4 V/cm4 V/cm

largemouth largemouth bassbass

2 V/cm2 V/cm

Fish examinedFish examined 1515 1616 2222

Vertebral fractureVertebral fracture 22 00 00

Vert. compressionVert. compression 66 00 00

Notochord herniaNotochord hernia 44 00 00

HemorrhageHemorrhage 22 00 22

Necrotic muscleNecrotic muscle 99 1010 44

Total fish injuredTotal fish injured 60%60% 63%63% 18%18%

Lesions in clinically normal Lesions in clinically normal bluegill after exposure to 8 bluegill after exposure to 8

V/cm for 5 sV/cm for 5 sFish examinedFish examined 1212

Vertebral fractureVertebral fracture 22

Vertebral comp.Vertebral comp. 22

Notochord herniaNotochord hernia 11

HemorrhageHemorrhage 33

Necrotic muscleNecrotic muscle 88

Total fish injuredTotal fish injured 67%67%

ConclusionsConclusions EmbryosEmbryos

More susceptible to DC than PDCMore susceptible to DC than PDC Most susceptible stage is near epibolyMost susceptible stage is near epiboly Exposure can induce premature hatchingExposure can induce premature hatching Even short exposure can be lethalEven short exposure can be lethal

Posthatching developmental stagesPosthatching developmental stages Newly transformed juveniles most Newly transformed juveniles most

susceptible to lethal effectssusceptible to lethal effects Susceptibility to electroshock-induced Susceptibility to electroshock-induced

mortality varies among speciesmortality varies among species

ConclusionsConclusions Newly transformed juvenile fish can be Newly transformed juvenile fish can be

injured by electric fieldsinjured by electric fields Injuries are seldom detectable by Injuries are seldom detectable by

gross, external examinationgross, external examination Microscopic injuries can be commonMicroscopic injuries can be common Injuries can be severe, including Injuries can be severe, including

vertebral fracturevertebral fracture Short exposure durations (5 s) can Short exposure durations (5 s) can

injure a high percentage of fishinjure a high percentage of fish

Implications for Threatened Implications for Threatened and Endangered Speciesand Endangered Species

Exposure of embryos:Exposure of embryos: Nest building species, all embryos exposed Nest building species, all embryos exposed

during a single electrofishing eventduring a single electrofishing event Spawning aggregations may be particularly Spawning aggregations may be particularly

vulnerablevulnerable Exposure of older life stages:Exposure of older life stages:

Newly transformed juveniles may be most Newly transformed juveniles may be most vulnerable and have highest mortalityvulnerable and have highest mortality

Tissue injuries may occur in most of the fish Tissue injuries may occur in most of the fish that are exposedthat are exposed

AcknowledgmentsAcknowledgments USFWS/AFS Fisheries Management USFWS/AFS Fisheries Management

SectionSection John Grizzle, Auburn UniversityJohn Grizzle, Auburn University

M.S. research assistant position announcement

Electrofishing publication list: pdf files available