Survival of Adult Spring Chinook from the Columbia River Estuary to Bonneville Dam
Background and Study Summary
Little is known about the behavior and survival of Columbia River Spring Chinook during the adult migration from the mouth of the Columbia River to Bonneville Dam (rkm 234), a key area of potential mortality. Estuarine mortality is a concern for Spring Chinook runs from the Snake and Upper Columbia River, which remain listed under the U.S. Endangered Species Act.
Contemporary estimates of the smolt–to–adult return rates for these fish are based on returns to Bonneville Dam. As such, mortality that occurs in the estuary or lower river is not distinguished from mortality in the ocean phase of the life cycle.
Commercial tangle–net crew hauling in a Chinook salmon.
Accurate escapement estimates, as well as information on estuarine and lower river residence, are essential for the successful management of tribal, commercial, and recreational salmon harvest. Fishery managers also need this information to make within–season adjustments to run forecasts, and it is critical for scientific studies designed to inform and aid recovery efforts.
Until recently, the logistics of collecting adult salmon in the estuary precluded research to mark these fish in sufficient numbers for unbiased survival estimates. We conducted a pilot study to evaluate a new adult capture and tagging methodology in spring 2010 and 2011 (Wargo Rub et al. 2012 a,b). Working in tandem with local commercial fishermen, we marked 962 returning adult spring Chinook salmon during the 2–year pilot study.
We estimated mortality rates of up to 24% for stock groups originating above Bonneville Dam and returning in 2011. This estimate was in addition to mortality due to harvest or from the sample procedure and was based on fish tagged during the peak of the adult Chinook run (13–22 April). Mortality for fish arriving earlier in the estuary was considerably lower, at 11%, and a mortality rate of only 2% was estimated for fish arriving near the end of the run season.
Similar patterns of mortality were observed in 2010. Along with identifying mortality in the estuary and lower river, these pilot studies demonstrated that adult salmon collected and tagged early in the study period tended to migrate more slowly to Bonneville Dam than did their cohorts sampled later.
Adult fish were collected by commercial fishermen with extensive experience in the use of tangle–net gear in the Columbia River estuary. Upon landing, fish with no obvious abnormalities on physical examination were placed individually into custom, PVC fish tubes and then transported from the sample boat to a NOAA Fisheries research vessel for sampling and tagging.
Adult Chinook salmon being transferred from the commercial fishing vessel to a research vessel using PVC tubes.
Study fish were scanned for a passive integrated transponder tag (PIT tag), and fork length was estimated from a metric ruler. If a tag was present, it was recorded and the fish was included in the study. If a PIT tag was not present, the fish was injected in the pelvic girdle area with a 134.2–kHz ISO PIT tag.
To identify whether fish had originated above or below Bonneville Dam, we sampled a small section of the pelvic fin from each study fish for genetic identification. After tagging and tissue collection, each fish was transferred back into a PVC tube and held in a recovery tank until release. After release, study fish resumed migration, and surviving fish passed PIT–tag monitors in the fish ladders at Bonneville Dam.
Custom–fabricated PVC tube, which facilitated safe handling, holding, and transfer of study fish.
After returns were complete, we downloaded the detection records from the PIT Tag Information System for the Columbia River Basin (PTAGIS), a publicly shared regional database.
The number of adults released at the river mouth was adjusted by subtracting the estimated harvest during the period just after release (commercial and recreational harvest estimates provided by the Washington and Oregon Departments of Fish and Wildlife). Estimates were also adjusted by the number of fish expected to succumb to gear effects, and the number of fish destined to enter tributaries or hatcheries below Bonneville Dam based on our own genetic analysis.
A final adjustment to our estimates was based on rates of detection efficiency at Bonneville Dam.
Study fish were physically restrained in dorsal recumbency for tissue collection and tagging.
This study provides unbiased, stock–specific point estimates of survival through the estuary and lower river for returning adults from Snake or Upper and Mid–Columbia River adult spring Chinook salmon stocks. Our estimates make the important distinction between mortality from harvest or from the sampling gear, and mortality that may be attributed to lower river predation.
Our work also provides estimates of run timing and residency in the estuary and lower river by upriver stocks. During the study period, we provided regular reports of our catch numbers to fisheries managers. Fisheries managers can also track our marked fish to Bonneville Dam online via PTAGIS. This information will assist managers in making adjustments to preseason run forecasts and in regulating the spring Chinook fishery.
Unbiased estimates of survival through the estuary are essential for evaluation of management strategies implemented during earlier life history stages. Without accurate data on adult mortality, the benefit to fish stocks from improvement to passage structures at hydroelectric facilities or from alternate transport release sites will likely be underestimated. Furthermore, research directed at resolving critical uncertainties in estuarine survival is called for in legal mandates for the recovery of endangered salmonids. (NMFS 2008; RPA 61).
More specifically, our study addresses the following high–priority research areas for salmon identified by the Pacific Fishery Management Council:
- Integrate genetic stock identification (GSI) methods into fishery management
- Improve forecasting
- Foster greater coordination, communication, and mutual respect between agency scientists and stakeholders
- Provide estimates of natural survival and run timing for adult spring/summer Chinook salmon through the estuary and lower river, an area not previously studied
- Provide valuable points of comparison between hatchery and wild stocks with regard to behavior and survival through the estuary and lower Columbia River.
Performance of upriver stocks should be measured from the time adults enter the estuary rather than from the time they encounter the first dam 200 km upstream. If mortality through the estuary and lower river is not systematically evaluated, we cannot accurately evaluate marine mammal control measures to increase adult survival to Bonneville Dam. Continuing to gather information on adult survival from the river mouth to Bonneville Dam is therefore critical.
In 2013, we plan to mark approximately 750 adult Chinook salmon as they enter the estuary. This sample should produce a survival estimate with a margin of error ≤5% based on detections at Bonneville Dam. We anticipate that approximately 2% of the adults we collect will have been PIT tagged as juveniles and can be included in our estimates.
We hope to evaluate either a purse seine or trap net, in addition to the tangle net, to identify the most benign and effective method of sampling adult Chinook salmon. Results from these evaluations will provide information about selective fishing methods and gear types for harvest investigations (NMFS 2008; RPA 62). Genetic data gathered for the study will provide a first step toward more comprehensive genetic stock identification monitoring (NMFS 2008; RPA 62).
We proposed this research as a collaborative effort between regional monitoring agencies and have worked to develop these collaborations. This approach will allow us to develop standard metrics for collection and dissemination of the information as we track and report on the status of adult fish migrating through the estuary and lower river.
A. Michelle Wargo Rub, Lyle G. Gilbreath, R. Lynn McComas, Benjamin P. Sandford, David J. Teel, and John W. Ferguson. 2012a. Estimated survival of adult spring/summer Chinook salmon from the mouth of the Columbia River to Bonneville Dam, 2010. Report of the National Marine Fisheries Service, Northwest Fisheries Science Center.
A. Michelle Wargo Rub, Lyle G. Gilbreath, R. Lynn McComas, Benjamin P. Sandford, David J. Teel, and John W. Ferguson. 2012b. Survival of adult spring/summer Chinook salmon from the mouth of the Columbia River to Bonneville Dam, 2011. Report of the National Marine Fisheries Service, Northwest Fisheries Science Center.
NMFS (National Marine Fisheries Service). 2008. Remand of 2004 Biological Opinion on the Federal Columbia River Power System (FCRPS) including 19 Bureau of Reclamation Projects in the Columbia Basin (Revised pursuant to court order, NWF v. NMFS, Civ. No. CV 01-640-RE (D. Oregon). NWR-2005-5883.