Integrated Forecasts of Fall Chinook Salmon Returns to the Pacific Northwest
Forecasts of returns are used to determine appropriate levels for ocean and in-river harvests of northeast Pacific fall Chinook salmon (Oncorhynchus tshawytscha). The current preseason forecasts are made by February, six months before fish arrive at natal rivers. As such, they do not capture ecosystem changes that occur after February. We incorporated catch and effort data from the Alaska summer commercial fishery to detect unusual ecosystem variability in fish return years and to update forecasts during the ocean fishery season. In addition, the traditional model using the ordinary regression unnecessarily has an intercept term, which often leads to unusual over-forecasts. Further there are concerns about autocorrelation in Chinook salmon returns. Finally the current practice does not provide information about the uncertainty inherent in the forecasts. To address these issues, we developed new forecast models and compared them with the traditional method. The models considered are: I, traditional preseason forecasts; II, autoregressive preseason forecasts without intercept term; III, ocean fishery real-time forecasts; IV, integrated forecasts from models I and III; and V, integrated forecasts from models II and III. We validated our models, using data from three Columbia River stocks [Upriver Bright (URB), Lower River Wild (LRW), and Mid-Columbia Bright (MCB)], and from two Canadian stocks [Fraser River Lates (FRL) and West Coast Vancouver Island (WCVI)]. Based on hindcasts of URB, LRW, FRL, and WCVI returns in 1992–2008 and of MCB returns in 1998–2008, model V was superior to the other models in bias and forecast coverage.
Hyun, S-Y., R. Sharma, J.K. Carlile, J.G. Norris, G. Brown, R. Briscoe, and D. Dobson. 2012. Integrated forecasts of fall Chinook salmon returns to the Pacific northwest. Fisheries Research 125-126:306-317.