Fraser River sockeye salmon: data synthesis and cumulative impacts

Fraser and non-Fraser sockeye populations. Hierarchical Bayesian methods areincreasingly common in applied fisheries science, and this particular case would seemto benefit from information-sharing among multiple stocks.Response: As discussed above, we did not have time to implement such approaches, thoughwe have now expanded our description of alternative modelling approaches.I expected this report on cumulative effects to provide a "systems" view of sockeyesalmon dynamics. That is, factors affecting sockeye dynamics do not necessarilyoperate independently, unidirectionally (i.e., all arrows point to only sockeye), andlinearly. Sockeye salmon populations influence, and are influenced by, many potentialfeedbacks within freshwater, river, and oceanic ecosystems.Response: We agree, and our conceptual model (while not representing all interactions forreasons stated above) do show various interactions amongst factors. However, our terms ofreference (Appendix 1) as well as those of the Cohen Commission(http://www.cohencommission.ca/en/TermsOfReference.php) are explicitly sockeye-centric,rather than ecosystem-centric. Therefore, we have been more focused on how variousecosystem stressors affect sockeye, rather than the reverse effects (how sockeye affectecosystems). To provide a more “systems” view, we’ve added some text under thediscussions of Plausible Mechanisms (e.g., in Section 4.2.1, we note that decliningabundances of sockeye result in less nutrients being transferred from marine to freshwaterecosystems, with potential negative effects on both subsequent generations of sockeye andother ecosystem components). In section 4.4.1, we discuss various ecosystem processesaffecting the degree of predation on sockeye in inshore areas. As discussed above, we havementioned feedbacks in Figures 3.3.1 and 2.3.1.This may reflect my ignorance, but has any research been done to determine whetherthe observed pattern in productivity is an expected result of Ricker-type stock-recruitdynamics? Are sockeye populations over-shooting some capacity limits and thereforeshowing natural signs of suppressed productivity? The abundances of sockeye duringthe 1990s and early 2000s were very high all over the northeast Pacific (includingAlaska), which may have lead to covariation in ocean growth and survival over broadspatial scales. I am not aware of recent research examining among-stock densitydependencein ocean survival of sockeye, even though it might be possible. Scientistshave argued for decades that massive enhancement of Japanese chum salmonsuppresses growth of North American chum salmon, so I wonder why similar argumentshave not been explored for sockeye.Response: The regression models we applied included Ricker-model representations ofdensity dependence for each stock. Ruggerone et al. (2010) have an excellent summary oftrends in wild and hatchery salmon populations, and note that hatchery-raised chum form62% of the combined total wild and hatchery salmon abundance. They also discuss thepotential for a “tragedy of the commons” effect in the North Pacific. Our analyses of theeffects of pink salmon abundance reflect potential competitive impacts of wild plus141