Introduction to Electrofishing

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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
INTRODUCTION TO ELECTROFISHINCETECTROFISHT]UG PRIIUCTPTESBoat CathodesMany aluminum electrofishing boats use the boathull as the cathode and the boom electrodes as theQ ( ^c^n (Janode. This is perfectly safe as long as you never a 300I=come in contact with the anode and complete the2q oelectrical circuit. The National Safety Council in-lE 200^^ iz-v ctheir data sheet #1-696-85 does not recommend -0)0)1 F ;Iusing the boat hull as the cathode, but we have o 100-.11.0 o,yet to hear of any accidents occurring because6v'wcof it.c)Figure 1l shows a Smith-Rootote barge(Lo 2 4 4 6 4 8 6 )designed for stream wading operations. NoteItttp Distance from center of anode (meters)the large cathode plate attached to the bottomEof the fiberglass hull. The anode is a pair of ringand gradientelectrodes about 28cm (1I") in diametermountedon fiberglass poles. With this arrangement, the associated with the larger cathode.resistance of the anode pair is four times the The SR-6 field tested with two 28cm anodes and a voltagecathode resistance. Thus, four times as much of 240 volts, showed good fishing effectiveness in 400voltage appears in the anode field as in the microSiemens/cc conductivity with a current of 3 to 4 amperes.cathode field, and consequently 80Vo of the In lower conductivities of 40 microSiemens/cc, a cunent of Iapplied voltage appears at each electrode. to 1.5 amp is effective. This data may serve as a useful benchmarkto judge whether a unit is operating under conditionsuchThe situation could be further improved byenlarging the cathode, but a point of diminishing that fish should be caught. If the electrical performance is closereturns is reached. Doubling the cathode size to this reference point, and fish are not being caught, it is safe towould halve the cathode resistance and give an 8 conclude there are few fish in the area.to I ratio between anode and cathode resistance.Now 887o of the voltage would appear at theanode. This is only an 87o improvement, andis not worth the additional physical problemsResistance ohmsof cathodeof anode fieldbetween anode and cathodePotential ditlerence voltsbetween cathode and waterbetween anode and watertotalCurrenl ampsPower kilowattsResislivity of the water in all cases=143Fmho/cmStandard 0.5#grid cathodes a.one$ anode35901251263244503.61.62b. twoanodes5085185265450592.38c. oneanodeI90993232432636128Figure 9. Gomparison of two sizes of cathode.d. twoanodesI50593023s6602.1522 www. smith-root.com'\Large wirenettingcathode\;-\ 'l\ Cathode plate\-l . iPulsatorFigure 11. Boftom mounted cathode plate on SR-6.t')eqfflqq(FGG(FGlaGG(FGGJ'J'GGGGGGGJ'J'GGGlFGu,]FGlt]FlFJlrF|Frlc'111
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Introduction to Electrofishing

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