2005 Evaluation of Chum, Chinook and Coho Salmon Entrapment near Ives Island in the Columbia River; 2004-2005 Annual Report.
- Pacific States Marine Fisheries Commission, Vancouver, WA
During mid-1990s, Pacific States Marine Fisheries Commission (PSMFC) and Washington Department of Fish and Wildlife (WDFW) identified several populations of salmon spawning approximately three miles downstream of Bonneville Dam on the Columbia River. These populations are exposed to rapidly changing flow regimes associated with Bonneville Dam's operation. This study investigated the relationship between changing water levels and stranding or entrapment of juvenile salmon in the Ives Island area. Walking surveys of the Ives Island and Pierce Island shorelines were conducted every one to three days throughout the juvenile emigration period. The nearby shorelines of the Washington and Oregon mainland were also surveyed. Between January and June of 2005, surveyors examined 21 substantial entrapments and 20 stranding sites. A total of 14,337 salmonids, made up of three species, were found either entrapped or stranded. Nearly 92% of the salmonids were chinook salmon (Oncorhynchus tshawytscha), 4.5% were federally listed chum salmon (Oncorhynchus keta), and 3.8% were coho salmon (Oncorhynchus kisutch). When compared to the 2004 study year, 2005 showed an 83% increase in the overall number of observed entrapped or stranded juvenile salmon. Much of this increase can be attributed to one entrapment found along the north shore of Pierce Island (identified as E501). E501 has historically been known to contain relatively large numbers of entrapped salmon. Even so, the number of entrapped salmon observed during 2005 was a 732% increase (5926) over any prior study years. Over 83% of all chum, 63.1% of all chinook, and 63.2% of all coho sampled during 2005 were retrieved from entrapments that were likely to have formed when Bonneville Dam tailwater levels dropped to elevations between 11.5 and 12.9 feet. Peak numbers of chum and chinook were sampled in mid-April when tailwater levels ranged between 11.6ft and 15.6ft. Peak numbers of coho were sampled during the last week of February, mid-March, and mid-April when tailwater level ranged between 11.4 and 14.3 feet, 11.5 and 15.3 ft, and 11.6 and 15.6 feet, respectively. The fork length data indicate that the majority of the entrapped and stranded salmon are in the 35-50 mm range. Stranded members of all three salmon species had mean fork lengths that were 8% to 30% shorter than those of their entrapped counterparts. The locations and habitat attributes of entrapments containing the majority of the observed juvenile salmon remain fairly constant from year to year. Changes in entrapment rankings appear to be more reflective of changes in prevailing tailwater levels than they are of changes in geography, vegetation, or fish behavior. Data collected over the past six study years indicates that there are entrapments that are capable of entrapping large numbers of salmon as various tailwater levels. Avoiding specific tailwater ranges may not minimize the impact of juvenile stranding. The only way to substantially minimize the impact of stranding is to allow no tailwater fluctuations or to only allow a steady increase of the tailwater level throughout the juvenile emigration period.
- Research Organization:
- Pacific States Marine Fisheries Commission
- Sponsoring Organization:
- United States. Bonneville Power Administration. Environment, Fish and Wildlife
- DOE Contract Number:
- 00004287
- OSTI ID:
- 897379
- Report Number(s):
- DOE/BP-00004287-4; R&D Project: 199900301; TRN: US200704%%790
- Country of Publication:
- United States
- Language:
- English
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