Fraser River sockeye salmon: data synthesis and cumulative impacts

Several analyses by MacDonald et al. suggest that contaminants are not a primary factor in thedeclining productivity of Fraser sockeye stocks (MacDonald et al. 2001; Executive Summary,Section 5.4). First, over the last 20 years, there is either no trend in the frequency ofcontaminants exceeding toxicity screening values, or a decreasing trend. If contaminants were animportant cause of declining sockeye productivity, contaminant concentrations should have beenincreasing over time. Second, various measures of sockeye productivity (freshwater, postjuvenile,overall life cycle) were not significantly correlated with a water quality index(incorporating conventional variables, major ions, nutrients, metals and phenols). Third, whilethe results of a sediment risk assessment showed that the concentrations of iron and nickel wereelevated at various locations within the basin, exposure to these contaminants of concern insediment is unlikely to be sufficient to adversely affect the survival, growth or reproduction ofsockeye salmon. However, the concentrations of selenium and dioxins occurred in salmon eggsat concentrations sufficient to adversely affect sockeye salmon reproduction, though themagnitude and extent of such effects could not be determined with existing data.Delayed Density Dependence. With the exception of the Quesnel sockeye stock, Peterman andDorner (2011; pg. 33-45) found little evidence in the Fraser system for increased spawnerabundance (and delayed density dependence) being the primary cause of declining productivity.They found little support for the idea that extremely large spawner abundances of sockeye (i.e.,"over escapement") reduced subsequent sockeye stock productivity. These analyses were basedon various analyses of indices of total productivity over the whole life cycle (i.e.,recruits/spawner), and therefore reflect the net effects across all life history stages.Christensen and Trites (2011) found that most of the candidate freshwater predators describedin section 4.2.1 are unlikely to have increased substantially during the period of declines insockeye productivity; the only possible remaining suspects are Caspian terns and double-crestedcormorants, as they do feed on sockeye smolts in freshwater and may be increasing inabundance. Data on freshwater predators are however very limited.Hinch and Martins (2011) did not conduct any statistical analyses relating temperatureconditions to indices of sockeye juvenile or life cycle productivity. Based on temperatureconditions and trends, as well as thermal optima for different sockeye life history stages, Hinchand Martins (2011) concluded that survival of eggs has possibly increased as a result of climatechange (but not in all stocks); survival of alevins is unlikely to have been affected; and survivalof fry in lakes has possibly decreased.While temperature changes or other factors may have resulted in changes in the abundance ofpathogens in spawning and rearing habitats, or sockeye susceptibility to such pathogens, the45