Fraser River sockeye salmon: data synthesis and cumulative impacts

Conclusion #1: Most other BC and Lake Washington sockeye stocks show a similar pattern ofdeclining productivity to that of most Fraser River sockeye stocks, especially since the late1990s.For 8 Fraser stocks that have juvenile data available, a similar analysis of spawner-to-juvenileand juvenile-to-recruit data showed very high correlation between juvenile-to-recruit andspawner-to-recruit trends, suggesting that most mortality associated with these productivity shiftsover the whole life span is occurring in the late juvenile to adult life phase (although it couldpossibly represent delayed mortality from a freshwater agent to which they were exposedearlier).An analysis of data for Tahltan age 1+ and age 2+ smolts compared survival rates for those thathave the same brood year but different ocean-entry year and found a correlation of r = 0.24. Butwhen data for smolts with the same ocean-entry year were compared instead, the correlationjumped to 0.56. The latter, higher correlation when juveniles have a shared ocean-entry year vs.the same brood year indicates that shared marine or late freshwater conditions dominate changesin productivity of these sockeye stocks.Conclusion #2: Most of the temporal changes in recruits/spawner arise in the marine and orfreshwater post-juvenile estimation stages. The Tahltan analysis indicates this is unlikely due todelayed mortality from a freshwater agent. Furthermore, the similarity of the productivity declinethroughout Washington and BC sockeye stocks, especially after around the year 2000, suggestspoor ocean conditions outside of Georgia Strait. This conclusion differs from the PSC workshopin June, because they have these new data now.Harrison sockeye, which have shown an opposite trend in productivity, enter the sea as fry (notsmolts) and are believed to migrate out through Juan de Fuca Strait, not Johnstone Strait.These results of a shared time trend in productivity of B.C. stocks, but the opposite trend forAlaskan stocks, would be consistent with a paper by Mueter et al. (2002, Can. J. Fish. AquaticSci. 59:456), which linked productivity declines in BC to increases in stock-specific locations forsummer sea surface temperature (SST) when juveniles enter the ocean. Specifically, changes inindividual sockeye stock productivity (log e (recruits per spawner)) per degree Centigrade increasein summer SST (SST coefficient) were graphed for stocks ranging from Washington and BCnorth to Alaska. The resulting graph showed a clear pattern of increasing productivity for Alaskastocks with increasing SST, and decreasing productivity for BC and Washington stocks withincreasing SST. Potential causes of this BC trend include a zooplankton-poor or predator-richenvironment when waters are relatively warm off the coast of BC.Brigitte DornerFurther analysis of sockeye productivity trends in relation to changes in summer sea surfacetemperature looked at the bigger picture coast-wide.Two types of animated graphs were shown. First was an animated map of the time-trend inindividual stock productivities for BC, with one map per year starting in 1950. During certainperiods, geographical clusters of Fraser River stocks (based on their spawning-ground location)appeared to change in similar ways. The other animated diagram showed stock-specificproductivities since 1950 (as derived from the Kalman filter analyses), illustrating in yet anotherway that when productivity for Fraser River and Washington stocks were generally declining,those in Bristol Bay were increasing over the same period.30