Standardizing the Electrofishing Fleet of Endangered Fish Recovery Programs in the Upper Colorado River Basin

Standardization of electrofishing operations requires the use of electrodes of similar configuration, spacing and electrical resistance. Standardizing the electrical waveform and power output requires the use of appropriate electrofisher control settings to maintain a constant transfer of electrofishing power across the range of water conductivities encountered. Endangered fish recovery programs in the upper Colorado River basin use electrofishing boats or rafts to capture fish at water conductivities ranging from 100 to 1,500 µS/cm. Boats provide increased mobility in larger rivers during high flows when water conductivities are typically lower and rafts are used on smaller rivers or during low flow periods when water conductivities may be higher. The recovery programs’ electrofishing fleet consists of seventeen 4.9-5.5 m long jon-boats and fourteen 4.3-4.9 m long rafts.  Electrode spacing, anode style (sphere) and size (23 cm diameter; half-submerged), cathode configuration, and the use of pulsed-direct current were standardized for each craft type. Boats used two anodes and the aluminum hull as the cathode. Rafts used a single anode and two trailing, multi-strand cable cathodes. The boat and raft cathodes had the same resistance (~20 Ω), but resistance of the rafts’s anode (~160 Ω) was more than twice that of the boat’s paired anodes (~60Ω). While a boat would electrofish about twice the area of a raft, it would require about three times the electrical power from the generator at the same applied voltage. The lower electrical power demand of a raft thereby allows it to effectively electrofish at higher water conductivities than a boat. Three models of electrofishers were evaluated to further promote standardization of the electrofishing fleet.