Effectiveness of Predator Removal for Protecting Juvenile Fall Chinook Salmon Released from Bonneville Hatchery, 1991

Despite a belief that removal of northern squawfish (Ptychocheilus oregonensis) would increase survival of juvenile salmonids (Oncorhvnchus spp.) in the Columbia River Basin, there has been no direct demonstration of the benefit of predator removal. In 1991, we assessed the survival increases for juvenile salmon before and after the removal of northern squawfish in the vicinity of the hatchery release site, while the U.S. Fish and Wildlife Service tested the effectiveness of electrofishing to remove northern squawfish. Short-term survival differences among release groups of juvenile salmon were assessed from comparisons of coded-wire tagged (CWT) fish recovered near the upper boundary of the Columbia River estuary at Jones Beach (River Kilometer 75). Captured northern squawfish were examined to determine the effects of predator size and density on the rate at which juvenile salmonids are consumed. 1993 NMFS (National Marine Fisheries Service) NWFSC (Northwest Fisheries Science Center) Library Public Domain 1861