Laboratory Design and Testing of an Electrical Crowder for Predator Deterrence

Fish screening facilities in the south Sacramento-San Joaquin Delta can provide favorable habitat for predator fish, primarily striped bass. At Tracy Fish Collection Facility (TFCF), striped bass reside upstream, downstream, and within the facility, feeding on seasonal influxes of smaller entrained fish. This study investigates the use of a fixed rolling electrical crowder as a safe and effective way of deterring large predator fish from taking up residency in the TFCF with little or no impact on smaller fish. The electric crowder consists of an electrofisher unit that transmits pulsed DC to an electrical sequencer. The sequencer transmits current to sets of electrode pairs such that the electrical field rolls in the downstream direction at a specified speed. The crowder rolls more slowly than the channel velocity to allow stunned fish to drift out of the field. Electrode spacing, polarity, and field strength were optimized in a laboratory model. Observations show that most adult striped bass 285 to 590 mm swam quickly out of the field while juvenile rainbow trout and Chinook salmon 88-108 mm were not greatly affected. Channel velocity did not affect response to the crowder; however, lighting conditions had a significant effect on behavior.