Development of a Systemwide Predator Control Program, Section II : Northern Squawfish Management Program Evaluation, 1996 annual report.
- Columbia Basin Fish and Wildlife Authority, Portland, OR
Predator control fisheries aimed at reducing predation on juvenile salmonids by northern squawfish Ptychocheilus oregonensis were implemented for the seventh consecutive year in the mainstem Columbia and Snake rivers. In this report, we (1) evaluate northern squawfish exploitation and size composition, and compare catch rate of incidentally-harvested fishes among the three major management fisheries in 1996, (2) estimate reductions in predation on juvenile salmonids since implementation of the fisheries, and (3) evaluate changes from 1990-96 in relative abundance, consumption, size and age structure, growth, and fecundity of northern squawfish. Systemwide exploitation of northern squawfish 2 250 mm fork length was 12.1% for sport-reward, 0.3% for dam-angling, and 0.5% for site-specific gill-net fisheries. Total exploitation was lowest in Lower Monumental Reservoir (0.0%) and highest in McNary Reservoir (18.2%). Mean fork length of harvested northern squawfish was 355 mm in the sport-reward, 391 mm in the dam-angling, and 408 mm in the gill-net fisheries. The dam-angling fishery had the lowest percentage (3.6%) of incidental catch relative to the total number of fish caught. Incidental catch was 27.0% in the sport-reward fishery and 54.6% in the gill-net fishery. If exploitation rates remain similar to mean 1991-96 levels, we estimate that potential predation by northern squawfish on juvenile salmonids in 1997 will be approximately 62% of predation levels prior to the implementation of removal fisheries. Further reductions in predation may be small, unless average exploitation in future years is higher than 1994-96 levels. Relative abundance of northern squawfish declined slightly from 1995 in Bonneville Reservoir, Lower Monumental Dam tailrace, and Little Goose Dam tailrace. Mean abundance for 1994-96 was 48-60% of 1990-93 levels among areas sampled at least five years. Indices of consumption were lower than 1995 in all areas except during summer in the tailrace boat-restricted zones of Bonneville and The Dalles dams. Predation indices have declined 69% from pre- 1994 levels. Decreases in proportional stock density were greater than could be explained by fluctuations in year-class strength, strongly suggesting that sustained removals may be altering the size structure of predator-sized northern squawfish. We found no evidence that northern squawfish have compensated in growth or fecundity in response to sustained exploitation.
- Research Organization:
- Columbia Basin Fish and Wildlife Authority
- Sponsoring Organization:
- US Bonneville Power Administration
- DOE Contract Number:
- 1994BI24514
- OSTI ID:
- 807818
- Report Number(s):
- DOE/BP-24514-7; R&D Project: 199007700; TRN: US200306%%297
- Resource Relation:
- Other Information: PBD: 1 Nov 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
Development of a Systemwide Predator Control Program, Section II : Northern Squawfish Management Program Evaluation, 1994 Annual Report.
Development of a System-Wide Predator Control Program: Stepwise Implementation of a Predation Index, Predator Control Fisheries, and Evaluation Plan in the Columbia River Basin; Northern Pikeminnow Management Program, 2000 Annual Report.