Introduction to Electrofishing

INTRODUCTION TO ELECTROFISHINGETECTROFTSHIiIG PRIIUCIPTES6.il6rh2) 10,18rn')2.tt7ril 2Il6.S3nt'0.00.20.4 0.60.8 1.01.2 1.4 1.61.82.O 2.2Distance from electrode centers (meters)Figure 7. Larger anodes increase the fishing area.2. The region affected by the electrode islimited to 5 to 10 radii.3 Electrode resistanceprimarily dependenton electrode radius, and varies in inverseproportion to radius.4. Forring electrodes, the cros section diameterof the ring material is of little importance.If the ratio of cross section diameter to ringradius is held constant. resistance variesinversely with ring radius.CATHODESIn electrofishing it is desirable to have a highvoltage gradient around the anode, and a lowvoltage gradient around the cathode.Figure 8 shows variation of voltage, as a functionof the distance from the fishing anode, for threetypes of cathode. It shows that it is advantageousto have the potential of the water as near aspossible to that of the cathode.The required voltage is reduced by diminishingthe resistance of the cathode field. Thiscompensates for the reduced resistance so that thecurrent does not vary. The power consumption isdirectly proportional to the voltage used.One advantage of a large cathode is that the riskof accidental electrocution is much reduced. Alarge cathode has very low potential with respectto the soil and the water around it. The resistancebetween the cathode and the water is halvedeach time the surface of the cathode is doubled. For example,a 100 square foot cathode would need another 100 square footadded to pass from g to 4.5 ohm. However a cathode larger than100 square feet would be inconvenient to handle for shore-sideelectrofishing.Figure 9 comparesmall and a large cathodes. With a standardgrid cathode, the anode voltage falls distinctly from 324 to 265volts when using two anodes. However with a very large rvirenetting cathod efficiency falls only slightly from324 ro 302volts when using two anodes.For shore-side operations, the cathode surface presents the leastresistance when it is divided into several parts placed severalmeters apart. An electrode is more effective when its form isleast concentrated. For example , a 3'Yl2' strip is more effectivethan a square of 6'Y6'.Figure 10 illustrates the variation in both voltage and gradientbetween the electrodes.Whenever possible, the cathode should be placed in parts of thestream that you do not wish to fish, or even in parts completelyseparated from the stream itself. The anode should never beallowed to come close to where the cathode is located.o(!= o(d500450400350200150o)N=(It\... Cathode Indentical to anode: 6OOV, 6.3kW=\\\\\\\\\\NN\\.o'\ro \ .EU)1000.5m2 grid cathode: 350V, S.7kW\llr..ooN5010m2 wire netting cathode: 310V,3.2kW\slss*s*.-...*.rr,.,.\00c) 2 4 6 4 4 4 6 4R O'ttoc(g Distance from center of anode (meters)Figure 8. Variation of voltage for three kinds of anode.www. smith-root.com21E oo o