Temporal P atterns in Productivity of North American Sockeye and Chinook Salmon

Although recent catches of salmon in the North Pacific are at record levels, relative catches of some species have declined. We used a Kalman filter estimation procedure to estimate time series of productivity values for North American Sockeye and Chinook salmon. Generally, Sockeye stocks in Alaska are experiencing above average productivity while stocks in British Columbia have experienced below average productivity since the early 1990s. Coast wide Chinook salmon stocks experienced poor productivity in the early 1990s but Alaskan and Upper Columbia River stocks have shown improved productivity for the last decade. Common temporal patterns in productivity across distant stocks and species may be useful in identifying shared environmental factors to explain observed variations in productivity. Introduction Recent salmon abundance in the North Pacific, as indexed by aggregate commercial catches has been among the highest on record, with no indication of decline (Irvine et al. 2009). In contrast, aggregate North American salmon catches have experienced a declining trend, with an increasing gradient from north (Alaska) to south (Canada and southern US). Although the total abundance of Pacific salmon remains high, trends in abundance patterns vary among species. Pink and chum salmon have consistently been the most abundant species and increasingly account for a greater proportion of the total catch. Catches of Chinook and Coho salmon have declined over the last two decades. High catches of pink and chum salmon have been attributed to the generally favourable climate-related marine conditions in the western North Pacific Ocean, expanding hatchery operations, and improving hatchery technologies. It is generally accepted that oceanographic regimes play a large role in the productivity of Pacific salmon species. Peterman et al. (1998) reported a positive correlation between time series of productivity indices for salmon stocks in close proximity, attributed to common local environmental experiences. We examined temporal trends in productivity of North American Sockeye and Chinook salmon to identify patterns that may contribute to our understanding of the factors that effect productivity of Pacific salmon. Methods We used a Kalman filter estimation procedure (Peterman et al. 2000; computer code from Dorner et al. 2008) to fit a Ricker model to spawner and recruit data for select North American sockeye and Chinook salmon stocks. The Ricker a parameter represents the average loge (recruits/spawner) at extremely low abundance of spawners. The Kalman filter estimation procedure assumes that the Ricker a parameter was not necessarily constant, and could change over time as a result of observation error as well as natural variation in year to year survival. The Kalman filter analysis removes some of the observation error and other variation not associated with systematic changes in productivity and provides time series of smoothed at values that reflect time-varying total-life-cycle productivity of salmon. Values are presented in standard deviation units (at value in a given year minus the mean stock-specific at , divided by the standard deviation of the at time series) which allows comparison of time trends across stocks.