The voltage gradients of electric fields produced by electrofishing boats are important in determining sampling efficiency and the potential for injuring fish. We evaluated 10 electrofishing boats and found that 3 boats had malfunctions that could impact sampling or operator safety. The in-water voltage gradients were measured for the remaining 7 boats to make comparisons among boats and to determine the voltage gradients present during electrofishing. For all boats evaluated, the cathode was the aluminum boat hull, and the 2 anode arrays each consisted of 3-11 droppers (cables, chains, or rods; 0.6-1.2 m long) suspended from a boom in front of the boat. A grid (1.5 x 2.0 m) was attached to the anode support booms between the anodes and the bow of the boat; this grid facilitated measurements of voltage gradients in the portion of the electric field where most fish are captured. For 9 locations defined by the grid and for 3 water depths (0.1, 0.5, and 1.0 m), a voltage gradient vector was calculated from the horizontal and vertical voltage gradients measured with a probe connected to an oscilloscope. With applied voltages of 900-1000 V, the mean voltage gradient for sampling locations within 1 m of the bow was 2.6 V/cm (SE, 0.1); means for individual boats ranged from 2.1 to 3.4 V/cm. In addition to measurements at locations defined by the grid, maximum voltage gradients of 16-20 V/cm were measured within 5 cm of anode droppers. Despite differences in equipment, the electrofishing boats produced electric fields with similar voltage gradients when measured at similar locations relative to the electrodes.
