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

摘要

Despite a belief that removal of northern squawfish (Ptychocheilus oregonensis)would increase survival of juvenile salmonids (Oncorhynchus spp.) in the Columbia River Basin, there has been no direct demonstration of the benefit of predator removal. In 1991, the authors 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. A total of 2,012 northern squawfish were removed from nine transect areas near the hatchery in about 20 hours of electrofishing between the two release dates. In 1989 and 1990, the differences in recovery percentages between the two release sites (no predator removal) were considerably greater and may have been related to lower river flows. They speculate that higher flow volumes in 1991 dispersed test fish more rapidly, reduced their exposure time to predation, and resulted in higher survival rates for Tanner Creek releases.