Fraser River sockeye salmon: data synthesis and cumulative impacts

correlated to other factors reflecting watershed position, including elevation and latitude, asnoted by Selbie et al. (2010).The available evidence does not support the hypothesis that exposure to water contaminantsduring the downstream migration could be a contributing factor to declines in Fraser sockeyeproductivity (MacDonald et al. 2011, Section 5.4). The post-juvenile index of sockeyeproductivity declined with increasing values of a water quality index for the migration period andzone (i.e. the opposite pattern from what one would expect if contaminants were a cause of theproductivity declines). There was no relationship between the water quality index and the fulllife cycle index of productivity. While the results of the sediment risk assessment showed thatthe concentrations of iron and nickel were elevated at two locations within the basin (LowerFraser and South Thompson Rivers), and have likely increased in the Lower Fraser, exposure tothese contaminants of concern in sediment is unlikely to be sufficient to adversely affect thesurvival, growth or reproduction of sockeye salmon.Hinch and Martins (2011) did not examine the effects of temperature on downstream migration,though section 1.5.1 of their report describes increasing temperatures in the Fraser River in latespring and early summer, and earlier timing of the spring freshet (about 6 days earlier than in the1950’s). Nelitz et al. (2011; Section 4.2; Table 17) used springtime air temperature as anindicator of the timing of ice break-up in nursery lakes (one of the cues of smolt outmigration),and tested the hypothesis is that if lake ice breaks up significantly earlier than experiencedhistorically, smolts would leave sooner, arrive in the Fraser estuary at the wrong time, andexperience lower productivity. They found that years with warmer spring time air temperaturesin nursery lakes were indeed associated with lower life cycle productivity in 14 of 18 Fraserstocks, but these negative correlations were weak and not statistically significant. The absence ofstatistical significance could be due either to the absence of a real relationship, or the fact thatfairly crude indicators (air temperatures) were used as predictors. In the recent PSC report onFraser sockeye, Peterman et al. (2010; section 4.6) found no change in the migration timing ofsmolts from Chilko Lake, and in Cultus Lake the median date of outmigration has shifted laterby about 13 days over the past 80 years (i.e., contrary to the expected response to climatechange). Better data are needed to assess trends in the timing of smolt outmigration relative tochanging climate conditions, and how this influences later survival once smolts enter the ocean.Harrison River sockeye have a different life history from the rest of Fraser River sockeyepopulations. They leave their rearing habitats as fry (sometimes called underyearling smolts) inthe year after spawning occurs (rather than in the second year after spawning), and reside in theFraser estuary for up to 5 months before entering the ocean. This life history would causeHarrison smolts to experience considerably greater exposure to contaminants and other stressors52