Fraser River sockeye salmon: data synthesis and cumulative impacts

summarize the following evidence of how warmer temperatures indirectly affect sockeye(references cited in their report):o along the British Columbia coast, warm SSTs are associated with reduced upwelling andhence low food availability (i.e. zooplankton) for young sockeye salmon;o the peak timing of the copepod Neocalanus plumchrus, the main zooplankter in the Straitof Georgia, has advanced up to 30 days in the past decades and the peak duration hasshortened in response to warming;o the observed advance in timing of the Fraser River spring freshet may also becontributing to an earlier peak in zooplankton density in the Strait of Georgia;o changes in food availability as well as high metabolic rates incurred by warm waters areconsistent with the observation that early marine growth of Fraser River sockeye salmonis reduced when coastal SST is warm;o reduced growth would make juveniles more vulnerable to predation mortality;o the abundance of non-resident predatory fish in coastal waters off British Columbiaincreases in warm years; ando resident predatory fish increase food consumption so as to offset high metabolic ratesincurred by warm watersConditions in Queen Charlotte Sound versus the Strait of GeorgiaOne of the most striking differences between the conclusions reached at the Cohen Commissionworkshop (Appendix 6) and the PSC report (Peterman et al., 2010) concerned the relativeimportance of ocean conditions inside versus outside the Strait of Georgia (SoG) during thecoastal migration of sockeye salmon to the Gulf of Alaska. Peterman et al. (2010) concluded thatit was “very likely” that physical and biological ocean conditions inside SoG during this lifestage had been a “major factor” contributing to the overall decline in productivity and “likely”that they had been a major factor contributing to the poor returns in 2009 13 . By comparison, thepanel concluded that it was “possible” that ocean conditions outside SoG had been a“contributing factor” to both the overall and 2009 patterns in sockeye salmon. However, themajority of the expert participants in the Cohen Commission workshop evaluated oceanconditions inside SoG as being only a “likely” contributor to both the overall and 2009 patterns,but that ocean conditions outside SoG, within Queen Charlotte Sound (QCS) in particular, were a13 The approaches used by Peterman et al. (2010) to assess the relative likelihood of different hypothese, as well asthe approaches used at the Cohen Commission Scientific and Technical workshop, were less formal than those weapplied in this technical report, and are not directly comparable. There were also differences in the group of expertsinvolved in making these assessments. For example, Peterman et al. (2010) gave ocean conditions inside the Straitof Georgia their highest possible likelihood rating and ocean conditions outside the Strait of Georgia a lowerlikelihood rating, whereas the participants at the Cohen Commission workshop concluded the reverse.64