Fraser River sockeye salmon: data synthesis and cumulative impacts

within-population, within-brood-year density-dependent effects to show what other variations(non-density-dependent effects) there are in survival rates. In addition, the Larkin model removeswithin-population density-dependent effects that occur among successive brood lines (across upto three successive brood years).We know the ocean environment is not stable and we’re interested in long-term signals, but thosesignals are clouded by observation error and natural variability, both of which are high-frequencypatterns compared to the long term trends. Kalman filter estimation, a standard method used inengineering to extract high-frequency noise from noisy data, was applied to the Ricker model toseparate the long-term, low-frequency signal from the noise.To test this method, the study built on previous work that simulated performance of parameterestimation procedures for both the standard Ricker model and the Kalman filter version of it. TheRicker model over-estimated productivity during low productivity periods (and under-estimatedproductivity when it was high), whereas the Kalman filter results provided a better fit with theactual data. In effect, this work showed that the Kalman filter was good at tracking changes inproductivity over time.The study applied the Kalman filter estimation method to both the Ricker and Larkin models,fitting a time-varying assumption for the a parameter (productivity) in both models. Examples ofdata processed with these various methods were then compared and the time trends inproductivity were much clearer when the high-frequency annual variability was removed.In addition to looking at trends for specific stocks, they looked for shared trends (or howindividual stock trends deviated from the overall trend). Early Stuart showed a long downwardtrend starting in the 1960s. Most of the individual Early Summer stocks showed downwardtrends. An exception is the Pitt River stock, which increased. Most Fraser Summers showed anupward trend until the early 1990s, followed by a downward trend. Harrison sockeye alsoshowed increasing productivity since the early 1980s. Quesnel showed a different pattern (littledecline since 1990). (The graphs all reflect standard deviation units so that the stocks could becompared).Lake Washington stocks showed a dramatic decrease in productivity starting in the late 1990s, apattern shared by Barkley sockeye stocks. Sampling has shown that juveniles of the LakeWashington stock migrate outside Vancouver Island, not through Johnstone Strait.Sockeye stocks from the BC Central Coast, the Skeena and the Nass all show similar decreasesin productivity from the late 1990s. Some of the declines started earlier (e.g. Rivers and SmithInlets), and some of them had a temporary increase in productivity prior to decreasing sharply inthe early 2000s.Further analysis of the Fraser sockeye trends showed that one principal component of the pattern(a long downward trend since the mid-1980s) accounts for 65% of the variation, while a secondcomponent (increasing trend in productivity until around 1990, then decreasing) explains 23%.Together these account for 88% of the changes over time, so they represent strong signals.These trends, as measured in standard deviation units and based on the smoothed Kalman filter,were also presented visually to demonstrate shifts in productivity over time for other BC,Washington and Fraser stocks. For the Fraser, this analysis showed declining productivity for allstocks since around 1990, except for the Harrison and Pitt river stocks, which showed increasingproductivity.29