Fraser River sockeye salmon: data synthesis and cumulative impacts

stressors. Thus our conclusions have a lower level of confidence than for Stage 1. While thereare some survival estimates for acoustically tagged smolts, these data (which only cover a fewstocks) were not analyzed by any of the Cohen Commission technical studies.As we found for Stage 1, none of the factors considered for Stage 2 is likely to have been muchworse in 2007 for downstream migrating smolts, sufficient to have significantly decreased smoltsurvival prior to entering the ocean, and affecting the 2009 returns. Ocean conditions in 2007are a very different story, discussed in the next section. Similarly, none of the factors affectingsmolt survival during their downstream migration are likely to have ben much better in 2008,sufficient to have substantially improved smolt to adult survival in the salmon returning in 2010.For example, Rensel (2010, Figure 4 in Appendix C of Peterman et al. 2010) found that FraserRiver flows in May were higher than normal in both 2007 and 2008.4.3.7 Key things we need to know betterSockeye smolt survival from rearing to the estuary is a significant gap in the current assessment.In the Columbia River, extensive PIT-tagging (Passive Induced Transponders) of hatchery fish(mostly chinook and steelhead) have provided precise estimates of in-river smolt survival rates,as well as smolt to adult survival rates, leading to considerable advancements in understanding(e.g., Schaller et al. 2007). The PSC Panel on Fraser sockeye declines (Peterman et al. 2010) hadthe following recommendations, with which we concur:“The survival rate of sockeye juveniles during their migration downstream within theFraser River cannot currently be estimated separately from the overall juvenile-to-adultsurvival rate. To identify the timing and location of sockeye mortalities, this limitationshould be (and can be) corrected. In the absence of correcting this issue, focusing researchmainly on marine conditions may be insufficient for improving understanding, forecasting,and management. The Panel recommends research to assess sockeye smolt survivalbetween lakes and the Fraser River estuary. The priority is rated higher for futuremanagement actions because corrective actions could be taken for disease and/orcontaminant problems, for example.” (Peterman et al. 2010; pg. 21)4.4 Stage 3: Coastal Migration and Migration to Rearing AreasThis stage covers the journey of sockeye salmon from the mouth of the Fraser River to the Gulfof Alaska.4.4.1 Plausible mechanismsAs shown in the conceptual model (Figure 3.3-1) potential factors affecting Stage 3 include: 1)pathogens and disease; 2) predators, 3) marine conditions, 4) Strait of Georgia habitat55