The effect of artificial illumination on Chinook salmon behavior and their escapement out of a midwater trawl bycatch reduction device

Abstract

The Pacific hake (Merluccius productus) midwater trawl fishery is the largest groundfish fishery off the U.S. West Coast by volume. Catches comprise mainly Pacific hake, however, bycatch of Chinook salmon (Oncorhynchus tshawytscha) can be an issue affecting the fishery as Endangered Species Act (ESA) listed Evolutionarily Significant Units represent a portion of the total Chinook salmon bycatch. We conducted two separate experiments evaluating the influence of artificial illumination on Chinook salmon behavior and their escapement out a bycatch reduction device (BRD) in a Pacific hake midwater trawl. In Experiment 1, we tested whether Chinook salmon could be attracted out specific escape windows of a BRD equipped with multiple escape windows using artificial illumination. In Experiment 2, we compared Chinook salmon escapement rates out of the BRD between tows conducted with and without artificial illumination to determine if illumination can enhance their escapement. Our results show that artificial illumination can influence where Chinook salmon exit out of the BRD, but also demonstrate that illumination can be used to enhance their escapement overall. As conservation of ESA-listed Chinook salmon is an ongoing management priority, our research contributes new information on how artificial illumination can minimize adverse interactions between the Pacific hake fishery and Chinook salmon.