Electrofishing boats: improved designs and operational guidelines to increase the effectiveness of boom shockers

An electrofishing power supply was developed to deliver up to 4.5 kW to stun fish. The control makes it possible to use a 3 phase 230 V, 4.5 kV A, 0.9 PF, 180 Hz alternator and deliver an output to the elctrodes of up to 500 V and up to 15 amperes as ac, de, or as a pulse train with a frequency from 5 to 120 Hz and with an "on time" from 10 to 50% of the period. Electrical safety was carefully considered in the design. Introduction Electrofishing makes use of electrical fields in the water to stun fish so they can be netted, examined, counted, and returned to the water as part of a fish census. It is important that the fish not be injured in the process. Alternating current in the water will stun the fish wherever the field is sufficiently strong while direct current fields will cause the fish to swim, involuntarily, to the positive electrode where they are stunned when they reach the strong field near the electrode. ,2 The electro fishing power supply and control was developed for the Wisconsin Department of Natural Resources. The system is mounted in a 16 or 18 foot aluminum flat bottom boat with electrodes at the bow and sides of the boat. Operators at the bow retrieve stunned fish near the bow electrodes with nets having insulated handles. These fish are placed in holding tanks where they recover in a few minutes and can be returned to the water. The basic power source is a 3-phase, 230 V, 4.5 kVA, 0.9 PF, 180 Hz alternator driven by a gasoline engine. An open delta transformer arrangement allows this voltage to be varied from 92 to 460 V. The 3-phase alternating current can be routed directly to the electrodes or can be rectified to provide a de output. The direct current power at up to 500 V and up to *By Theodore Bernstein, Electrical Eng. Dept., and Harry H. Miller, Instrumentation Centei;, Univ. of Wis. Reprinted from Proc. 1973 IEEE Southeast Conf. Cat. No. 73, CH0785-2, REG III. 15 amperes is switched by means of a solid state SCR control. This direct current output to the electrodes can be either on continuously, off, or it can be delivered as a pulse train output with a frequency range of 5 to 120 Hz and an "on-time" of 10 to 50% of the period. The great variability of the output is useful in investigating the fish-stunning ability of direct and alternating currents as well as combinations of both on various species of fish. The pulsed output makes it possible to use instantaneous power higher than the continuous duty rating of the alternator. The variation in voltage is used to obtain suitable current levels for a wide range of lake conductivities. Electrical safety was one of the most important design parameters. The generators used in electrofishing provide more than enough voltage and current to electrocute a person. System Operation Figure 1 shows a system block diagram for the electrofishing power supply. The engine-driven alternator, 3-phase output is routed to the transformer panel through a contactor. This contactor opens the circuit in the event one of the safety interlock switches opens indicating an operator on the boat is out of position. The