Electrofishing

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

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

Basic types of electrofishing units:• Backpack: electrodes and generator; battery or

gas-powered control unit.

Smith RootModel LR-24, 24 volt battery

Ours was manufactured by Coffelt

Basic types of electrofishing units:

Shore unit - generator powered control unit, cables, and electrodes.

Safety first!!!

1. All workers wear • life jackets, high• voltage gloves• rubber boots

2. Adequate numbers and placement of shutoff switches

3. Avoid inclement weather, lightning, etc.

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 waveformDirect currentPulsed DC waveform

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

Current characteristics continued:Pulse width - “on” time of a DC pulse

•80% duty cycle (drawn on board)•50% duty cycle

Generally accepted:• DC is less damaging than AC

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)

Voltage

Current

Draw on board

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

Boat electrofishing

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

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

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

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

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.

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.

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

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