Introduction to Electrofishing

INTRODUCTION TO ELECTROFISHINGETECTROFISHIIUG PR|n|CIPLESelectrodes. Note that the 20cm electrode reaches outfafther, producing 7 volts head-to-tailbetween 1.0 and 1.2l. Larger electrodes have lower resistance, need moremeter from the electrode; as opposed to only 4 volts forcurrent at given voltage, reach out farther, and havethe smaller electrode at the same distance. Note also thatlower maximum voltage gradient.the voltage the fish receives closer to the electrode is less2. Small electrodes pose a hazard to fish because offor the larger electrode (100 volts instead of 144 volts).high cunent density and voltage gradient.Larger electrode thus offers two advantages: greaterange,3. Electrodes placed farther apart use less current, butand lower maximum gradient.the savings are not large.One drawback is that a larger electrode also has greater4. The resistance of an electrode varies in directcircuit loading, and thus draws more cunent for the same proportion to water resistivity.voltage (twice as much for the double size electrode).Thus, a larger electrode requires a larger generator. This RING ELECTRODESdictates a practical upper limit on electrode size for a 1. Once spacing exceeds 10 radii, the distance betweengiven generator and water conductivity. Except for this electrodes is insignifi cant.limitation, the larger the electrode, the better the fishingeffectiveness and the easier it is on the fish.Figure 7 shows that larger electrodes increase the fish'lOcmcollection area. The shaded areas have a voltage gradientbetween 0.12 and 1.2 volts per cm, and are suitable forelectrofishing. The applied voltage is 300 volts.o(sIooouJFigure 4. The field pattern, and the variation of gradientbetween two electrodes.20 www.smith- root.comELECTRODE BEHAVIOR0.0 0.2 0.4 0.6 0.8 1.0 1.2Distance from electrode centers (meters)Figure 5. Gomparison of two sizes of anode.11 2r100 66144 >' I'-il,l;I100 )'.,+II1oo:1r44 'ft 16 +-1+ 10i volts i66 502rlttvolts8rtzkrt -II- t -III400.0 0.2 0.4 0.6 0.8 1.0 1.2Distance from electrode centers (meters)Figure 6. Comparison of effects of two sizes of anode.I3rlllI4(I{ rI4r-l11Fl4F1qadV'IV';FIv.FFFFFFFFFFFFFFvGGGUtFtFGGGGGGJrGG