2Electrofishing• 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
3Basic types of electrofishing units: Boat: generator and control unit in boat.
5Basic types of electrofishing units: Backpack: electrodes and generator; battery or gas-powered control unit.
6Smith RootModel LR-24, 24 volt batteryOurs was manufactured by Coffelt
7Basic types of electrofishing units: Shore unit - generator powered control unit, cables, and electrodes.
8Safety first!!!All workers wearlife jackets, highvoltage glovesrubber bootsAdequate numbers and placement of shutoff switchesAvoid inclement weather, lightning, etc.
9Current 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 currentPulsed DC waveform
10Current characteristics continued: Frequency = total # of cycles per time unit = hertz (Hz)1 Hz = 1 cycle per secCommon: ppsOthers:5-40 pps, spiny-rayed fish3-5 pps large catfishpps, small fish
11Current characteristics continued: Pulse width - “on” time of a DC pulse80% duty cycle (drawn on board)50% duty cycle
12Generally accepted:• DC is less damaging than AC
13Anode - positive electrode Cathode - negative electrodeConductivity - 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)
15Behavior and physiology: electrotaxis = forced swimming induced by any kind of electrical currentAC - forced swimming without orientationDC - forced swimming toward anodenarcosis = muscular relaxation, may still swimtetany = state of muscle rigidity; fish immobilized
17Species effectively captured • Most effective for near-shore, shallow habitat• Essential for sampling largemouth bass• Smallmouth bass, sunfishes, trouts
18Influence of water conductivity • Major factor affecting electrofishing effectiveness• Peak effectiveness at perhaps uS/cm?• Likely because, within this range, power transfer into fish from water is maximized.• Should always record conductivity
19Low conductivity waters • Requires high voltage, less current• Try high voltage (perhaps V) at low amperage• A large ground (negative electrode) may also help• Equipment may be “voltage-limited,” that is, cannot supply the required voltage
20High 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
21Problems of High Conductivity • sample at night• fish are less likely to run from yousmall, intense field is more likely to get them at night, especially if the dipper goes on and off the pedal.
22As 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.
23Day 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
24Considerations• When properly used, most fish can be released alive• Some concerns over fish injury; salmonids are especially sensitive