Spawner-Recruit Analysis and Escapement Goal Recommendation for Chinook salmon in the Kuskokwim River Drainage

Alaska Department of Fish and Game, Fishery Manuscript Series No. 12-08, Anchorage

Using 1976–2011 estimates of annual run size, harvests, and age-composition from a reconstruction analysis, a spawner recruit analysis was conducted for Chinook salmon Oncorhynchus tshawytscha of the Kuskokwim River drainage, and the results used to select a drainagewide escapement goal.  For estimation of the spawner–recruit parameters, we employed a Bayesian state-space modeling method that explicitly incorporated uncertainties associated with the size of annual run and escapement and age composition, as well as serial correlation and missing data.  The analysis found that the stock is highly productive and does not show evidence of overharvest.  Based on expected yield predictions from the spawner-recruit model, we recommend a drainagewide sustainable escapement goal (SEG) of 65,000–120,000 Chinook salmon.  The goal will provide expected yields greater than 100,000 Chinook salmon, adequate for subsistence needs, and it has a lower bound that was chosen conservatively as an escapement equal to the lowest documented escapement from recent years that produced recruits adequate for subsistence needs. From the drainagewide escapement goal, three sustainable escapement goals were derived for the Kwethluk, George, and Kogrukluk rivers, for which Chinook salmon escapements are monitored annually with weirs, by multiplying the upper and lower bounds of the drainagewide goal by the mean proportion of tributary escapement to drainagewide escapement. Recommended tributary SEGs are 1,800–3,300 for George River, 4,800–8,800 for Kogrukluk River, and 4,100–7,500 for Kwethluk River.  Discontinuation of the escapement goal for Tuluksak River was also recommended.