Cohort analyses and new developments for coded wire tag data of Atnarko River Chinook salmon
The Coded Wire Tag (CWT) workgroup of the Pacific Salmon Commission (PSC) recently identified that major Chinook salmon (Oncorhynchus tshawytscha) production regions and life histories are poorly represented by CWT indicator stocks currently used for assessments by the PSC Chinook Technical Committee (CTC). One of these major production areas without a CWT indicator stock is the central coast of British Columbia, where the abundance of Chinook salmon spawners is dominated by returns to the Atnarko River in the Bella Coola River watershed. Although the Bella Coola River watershed has had the most intensive assessment in central British Columbia, including the most thorough escapement assessment in the region, and in spite of Atnarko Chinook being CWTed since 1976, significant issues have prevented the inclusion of this population as a CWT indicator stock in PSC assessments: (i) a need for validation of the quality of estimates of total escapement; (ii) the need for adequate sampling allowing estimation of freshwater CWT recoveries; (iii) data coordination reporting problems; and, (iv) limitations of funds to conduct robust and effective sampling and analysis. The main objectives of this investigation were to compile, evaluate, and improve the Atnarko Chinook CWT recovery data from freshwater fisheries and escapement, and then use these data for cohort analyses. Cohort analysis is the reconstruction of the exploitation and spawning history of a stock using CWT release and recovery data to estimate key population statistics, such as survival, maturation, and exploitation rates. The successful completion of cohort analyses for this stock contributes to the goal of incorporating Atnarko Chinook into future CTC assessments to better represent life histories and exploitation patterns of central British Columbia Chinook salmon populations.