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Research on Effects of Electrofishing

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  1. Research on Effects of Electrofishing Ted Henry, Adjunct Assistant Professor Dept of Forestry, Wildlife, and Fisheries University of Tennessee, Knoxville, TN • USFWS proposal: Effect of Electroshocking on Native Southeastern Fishes with Emphasis on Species Protected under the Endangered Species Act • J.R. Shute, P. Rakes (Conservation Fisheries Inc.) • Support for graduate research assistant (M.S.) to begin fall 2006 (Dept FWF, UTK) • Project objectives • Additional funding

  2. Overall Objectives for Electrofishing Injury Research • Consider effect of different electric field types (e.g., DC PDC) and investigate: • Survival of embryos • Survival of vulnerable older life stages • Sub-lethal injury to tissues • Consider T&E species or surrogates • Darters, madtoms, and shiners

  3. 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?

  4. Previous Electrofishing Injury Research • Projected funded by the USFWS through the Fisheries Management Section of AFS • Examined effects of electrofishing in early life stages of warmwater fish (focused mostly on sportfish) • Laboratory based research with field validation • Results indicate that investigations on effects on T&E species are necessary

  5. Research Methods Modified electrofishing pulse box Oscilloscope Aluminum plate electrodes homogeneous electric field 30 cm Model of exposure chamber

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

  7. Survival of Largemouth Bass Embryos after Exposure to 8 V/cm Similar results for bluegill embryos Control (survival 83%) Hatching 48 h

  8. 25 mm channel catfish

  9. Age-related Mortality of Largemouth Bass 60-Hz PDC cm

  10. Electroshock-Induced Mortality of Newly Transformed Juvenile Fish Largemouth bass Blackbanded darter* Channel catfish Rainbow trout Nile tilapia 60-Hz PDC for 20 s *adult

  11. Grossly Visible Injuries

  12. spinal cord vertebra control notochord channel catfish anterior tail sagittal section dorsal aorta compressed vertebra electroshocked 20 s, 4 V/cm, 60-Hz PDC

  13. bluegill anterior tail sagittal section electroshocked 5 s, 8 V/cm, 60-Hz PDC Fractured vertebra (arrow) and hemorrhage (H) live fish had no indications of injury H

  14. Rainbow trout anterior tail sagittal section electroshocked 20 s, 4 V/cm, 30-Hz PDC Notochord hernia protruding between vertebrae notochord hernia spinal cord live fish had paralysis of the tail and posterior trunk vertebrae

  15. Nile tilapia anterior tail sagittal section electroshocked 20 s, 16 V/cm, 60-Hz PDC live fish had uncoordinated swimming Necrotic muscle (arrows) necrotic muscle also found in control fish: 1 largemouth bass and 1 bluegill

  16. Histopathology of Clinically Normal Fish 1 Hour After Electroshock

  17. Lesions in clinically normal bluegill after exposure to 8 V/cm for 5 s

  18. Conclusions • Embryos • More susceptible to DC than PDC • Most susceptible stage is near epiboly • Exposure can induce premature hatching • Even short exposure can be lethal • Posthatching developmental stages • Newly transformed juveniles most susceptible to lethal effects • Susceptibility to electroshock-induced mortality varies among species

  19. Conclusions • Newly transformed juvenile fish can be injured by electric fields • Injuries are seldom detectable by gross, external examination • Microscopic injuries can be common • Injuries can be severe, including vertebral fracture • Short exposure durations (5 s) can injure a high percentage of fish

  20. Implications for Threatened and Endangered Species • Exposure of embryos: • Nest building species, all embryos exposed during a single electrofishing event • Spawning aggregations may be particularly vulnerable • Exposure of older life stages: • Newly transformed juveniles may be most vulnerable and have highest mortality • Tissue injuries may occur in most of the fish that are exposed

  21. Acknowledgments • USFWS/AFS Fisheries Management Section • John Grizzle, Auburn University M.S. research assistant position announcement Electrofishing publication list: pdf files available