Fraser River sockeye salmon: data synthesis and cumulative impacts

Peterman and Dorner (2011) have three key findings regarding the patterns of change in sockeyeproductivity:1. Life history stages of Fraser sockeye showing declining productivity. Of the nineFraser sockeye stocks with data on juvenile abundance (Figure 13 in Peterman andDorner 2011), only Gates sockeye have showed declines in juvenile productivity (i.e.,from spawners to juveniles) but 7 of the 9 stocks showed consistent reductions in postjuvenileproductivity (i.e., from juveniles to returning adult recruits). These resultsindicate that either: 1) the primary mortality agents causing the decline in Fraser Riversockeye occurred in the post-juvenile stage (i.e. after fry or smolts were enumerated), or2) that certain stressors that affected juveniles were non-lethal in fresh water but causedmortality later in the marine sockeye life stage. Note that mortality during over-winteringin nursery lakes (for most stocks), or during pre-smolt and smolt downstream migrationwould be ascribed to the post-juvenile stage. Unfortunately, juvenile data series for non-Fraser stocks are either very short or not available at all, making it difficult to judge towhat degree similarities in juvenile-to-adult survival rates are shared among B.C. stocksoutside the Fraser (Appendix P3 in Peterman and Dorner 2011).2. Stocks showing declining productivity. Within the Fraser watershed, 17 of 19 sockeyestocks have shown declines in productivity over the last two decades. Both Fraser andmany non-Fraser sockeye stocks, in Canada and the U.S.A., show a similar recentdecrease in productivity. Thus, this trend has occurred over a much larger area than justthe Fraser River system and is not unique to it. This is a very important new finding.Specifically, based on smoothed estimates of productivity trends via a Kalman filter (thethird productivity measure described above), there have been relatively large, rapid, andconsistent decreases in sockeye productivity starting in the late 1990s in many areasalong the west coast of North America including the following stocks (from south tonorth): Puget Sound (Lake Washington), Fraser River, Barkley Sound on the West Coastof Vancouver Island (Great Central and Sproat Lakes), Central Coast of B.C. (LongLake, Owikeno Lake, South Atnarko Lakes), North Coast of B.C. (Nass and Skeena),Southeast Alaska (McDonald, Redoubt, Chilkat), Yakutat (northern part of SoutheastAlaska; East Alsek, Klukshu, Italio). These patterns are illustrated in Figures 4.1-3 and4.1-4.3. The timing of productivity declines. There have been three separate phases of decline inproductivity since 1950. The first started in the 1970s, the second in the mid-1980s, andthen the most recent one in the late 1990s or early 2000s, with individual stocks showingthese trends to various extents. Furthermore, periods of low productivity in southern31