METHODS OF OPERATION OF ELECTRIC SHOCKERS 



The size and construction of the electrodes, 

 the methods of "fishing" the anode, and the 

 abilities and experience of the operators can 

 be as important in electrofishing as the use 

 of an optimum output current. In the following 

 section we discuss equipment and procedures 

 that we have found to be successful in the field. 



ELECTRODES 



The electric energy in water can be in- 

 creased by the use of "optimum- sized" elec- 

 trodes. The maximum surface area of the 

 electrode is governed by the practicality in 

 manipulating it- -especially the anode, or fish- 

 attracting pole, which should be highly mobile 

 and of a size that can be passed through swift 

 waters without excessive difficulty. The con- 

 ductive grid of the anode is best when about 

 40 cm. square. This size of grid actually 

 hinders conduction in nnost waters, but the 

 increased current densities immediately sur- 

 rounding the anode (fig. 3) facilitate electro- 

 narcosis which eases problems of capturing 

 fish. 



The electrical resistance inherent with small 

 anodes can be overcome with the use of en- 

 larged cathodes in practical stream operations 

 because the cathode can be stationary. The 

 optimum size for the cathode is dependent 

 upon the water resistivity. The suggested 

 minimum cathode surface area for waters 

 less than 30,000 ohm cm.^ is 2.3 m. square, 

 but for more resistive waters the cathode 

 size should be increased. 



The most satisfactory cathode is an alumi- 

 num boat, since it can also be used to trans- 

 port the shocker and fish- holding tubs. Some 

 caution must be used with a boat cathode. The 

 operators can receive shocks by placing one 

 hand on the boat and the other in the water 

 simultaneously, and gear-damaging short cir- 

 cuits can result if the anode touches the boat. 

 Weighted-down metal hardware cloth serves 

 as a good cathode in small streams where 

 mobility is not required. Galvanized washtubs 

 are often used as cathodes for convenience, 

 but are not highly recommended, especially 

 if the stream is resistive. Because electrical 

 resistance increases with distance between 

 the electrodes, the anode is usually fished 

 within 1 5 feet of the cathode. 



ELECTROFISHING TECHNIQUES 



On(t engaged in electrofishing must wade or 

 float, depending upon the depth or swiftness 



of the water. In suitable waters, the opera- 

 tors wade and can probe the anode into likely 

 fish habitat (fig. 9). Wading upstream elimi- 

 nates effects of turbidity caused by bottom 

 sediment. Furthermore, if collections are for 

 a food-habit study, stunned prey are not swept 

 downstream and consumed by predators. H 

 turbidity and predation are unimportant, how- 

 ever, collections can be made more effi- 

 ciently and less strenuously when moving 

 downstream. The fish are normally oriented 

 upstream, or toward the descending electrical 

 field, and the shocked fish initially induced 

 into flight bolt upstream into higher voltage 

 densities, where they are held. Fish that 

 manage to escape are often captured a short 

 distance downstream. The size of the fish 

 captured by wading operations in large streams 

 is usually less than 150 mm., whereas larger 

 fish are taken in deep waters by the floating 

 method. 



The floating method of electrofishing is 

 used when the stream is too deep or swift to 

 wade (fig. 10). The anode is clamped rigidly 

 ahead of the boat, extending into the water. 

 One man guides the boat with oars while one 

 or two operators dip fish as the boat drifts 

 with the river. 



Collecting can be improved furthe r by intro- 

 ducing the element of surprise through inter- 

 mittent fishing. The intensity of the anode's 

 peripheral electric energies only frightens 

 fish, causing them to bolt or penetrate deeper 

 into cover. In either situation, chances of 

 capture are reduced. It is better not to move 

 through a body of water with the power con- 

 tinuously on, but rather to fish only in likely 

 habitat. Fish can be extracted from areas of 

 heavy cover or from under shore ice by in- 

 serting the anode, turning the power on, and 

 withdrawing the anode slowly and smoothly. 

 Fish follow the anode under the influence of 

 galvanotaxis into the open, where they can 

 be netted. If the stream velocity is appreci- 

 able, the electrical power can be left on during 

 floating without loss in efficiency. 



Night fishing with lights has proven to be 

 exceedingly productive in lakes (Loeb, 1957; 

 Johnson, 1960; and Latta and Meyers, 1961), 

 but it is not so in streams. The reflection 

 and refraction of the spotlight beam caused 

 by the ruffled stream surface greatly impair 

 sighting of the fish. Headlamps are useful 

 for electrofishing by wading. 



