Fraser River sockeye salmon: data synthesis and cumulative impacts

2010) and the Strait of Georgia has the highest harbor seal density anywhere in the world,implying exposure to both of these potential predators.The data on Fraser River sockeye salmon recruits, by stock and by age-type (i.e. differentiatingamong fish that enter the ocean or return from the ocean earlier or later than the dominantbehavior pattern), suggest that since the mid-1970s or early 1980s, the variability in theproportion of sockeye salmon returning at age-5 (rather than the dominant age-4) has beenincreasing. Figure 4.5-1 shows the proportion of adults returning in year 5 for the Early Stuartstock, as one example of this pattern. This particular example demonstrates several generalpatterns: 1) after 1980, the proportion of the stock returning in year 5 is never zero; 2) theaverage proportion of sockeye spending an additional year in the ocean before returning tospawn appears to be increasing over time, especially after approximately 1980; 3) the year-toyearvariability also appears to be increasing after approximately 1980; and 4) there areoccasional years where the proportion of Year-5 sockeye is several times greater than average.Rigorous statistical analyses of this potential phenomenon have not been conducted in thepresent project, but preliminary investigations have found that to varying degrees these types ofpatterns also appear to occur within many other Fraser River sockeye salmon stocks. Thiswarrants further analysis, because if these patterns are shown to be consistent across stocks, itwould present evidence suggesting that Fraser River sockeye salmon have been increasing theduration of their exposure to potential stressors encountered in the open ocean.Figure 4.5-1. The proportion of Early Stuart sockeye returning as 5-year old adults.74