Electrofishing

1. Electrofishing

2. Electrofishing • Electrical current is used to stun fish so they can be netted by a biologist • A generator supplies the electricity • A control unit allows the biologist to monitor the voltage and amperage of the electrical field to minimize fish injury and mortality

3. Basic types of electrofishing units: • Boat: generator and control unit in boat.

5. Basic types of electrofishing units: • Backpack: electrodes and generator; battery or gas-powered control unit.

6. Smith Root Model LR-24, 24 volt battery Ours was manufactured by Coffelt

7. Basic types of electrofishing units: Shore unit - generator powered control unit, cables, and electrodes.

8. Safety first!!! • All workers wear • life jackets, high • voltage gloves • rubber boots • Adequate numbers and placement of shutoff switches • Avoid inclement weather, lightning, etc.

9. Current characteristics Alternating current (AC) = characterized by a sequence of + and - waves that are equal, sinusoidal, and follow each other alternately at regular time intervals. On board: AC waveform Direct current Pulsed DC waveform

10. Current characteristics continued: • Frequency = total # of cycles per time unit = hertz (Hz) • 1 Hz = 1 cycle per sec • Common: 50-60 pps • Others: • 5-40 pps, spiny-rayed fish • 3-5 pps large catfish • 40-120 pps, small fish

11. Current characteristics continued: • Pulse width - “on” time of a DC pulse • 80% duty cycle (drawn on board) • 50% duty cycle

12. Generally accepted: • DC is less damaging than AC

13. Anode - positive electrode Cathode - negative electrode Conductivity - capacity of ions in solution to convey an electrical current; directly related to inorganic dissolved solids (cations, e.g., Ca, Al, Mg, Na, and anions, e.g.., chloride, sulfate, nitrate)

14. Voltage Draw on board Current

15. Behavior and physiology: electrotaxis = forced swimming induced by any kind of electrical current AC - forced swimming without orientation DC - forced swimming toward anode narcosis = muscular relaxation, may still swim tetany = state of muscle rigidity; fish immobilized

16. Boat electrofishing

17. Species effectively captured • Most effective for near-shore, shallow habitat • Essential for sampling largemouth bass • Smallmouth bass, sunfishes, trouts

18. Influence of water conductivity • Major factor affecting electrofishing effectiveness • Peak effectiveness at perhaps 100-400 uS/cm? • Likely because, within this range, power transfer into fish from water is maximized. • Should always record conductivity

19. Low conductivity waters • Requires high voltage, less current • Try high voltage (perhaps 400-500 V) at low amperage • A large ground (negative electrode) may also help • Equipment may be “voltage-limited,” that is, cannot supply the required voltage

20. High conductivity • Requires high current, less voltage • Up to perhaps 1,000 uS/cm, we seem to obtain useful sample • Above 2,000 uS/cm, it really becomes hard to even get a sample • Problems from power limitation of the gear (too much current required), and large inefficiency of power transfer from water to fish

21. Problems of High Conductivity • • sample at night • • fish are less likely to run from you • small, intense field is more likely to get them at night, especially if the dipper goes on and off the pedal.

22. As conductivity increases, decrease electrode size. • Done to decrease current drain on generator. • Get more voltage at the same amperage. • Submerge 50% of an electrosphere at 1,200 uS/cm conductivity, output meters read 120 V at 10 A. • Submerge 20%, 200 V, and perhaps only be at 7-8 A. • However, electric field configuration changes.

23. Day vs. night electrofishing • More and larger LMB at night • General consensus is to electrofish at night in clear waters and in high water conductivity • Complex habitat - day for safety reasons

24. Considerations • When properly used, most fish can be released alive • Some concerns over fish injury; salmonids are especially sensitive