Abnormal Migration Timing and High en route Mortality of Sockeye Salmon in the Fraser River, British Columbia

Abstract

Since 1995, several stocks of Fraser River sockeye salmon (Oncorhynchus nerka) have begun upriver spawning migrations significantly earlier than previously observed. In some years, the timing of peak migration has shifted more than 6 weeks. Coincident with this early migration are high levels of en route and pre‐spawning mortality, occasionally exceeding 90%. These phenomena pose risks to the perpetuation of these fisheries resources. At present, although there are many competing hypotheses (e.g., energetics, osmoregulatory dysfunction, oceanic conditions, parasites) that may account for early migration and high mortality, there are no definitive answers, nor any causal evidence that link these issues. With poor predictive ability in the face of uncertainty, fisheries managers have been unable to effectively allocate harvest quotas, while ensuring that sufficient fish are able to not only reach the spawning sites, but also successfully reproduce. If trends in mortality rates continue, several important sockeye salmon fisheries and stocks could collapse. Indeed, one sockeye stock has already been emergency listed as endangered under Canadian legislation.

Integrating climate-related stressor effects on marine organisms: unifying principles linking molecule to ecosystem-level changes

“…Differences between stocks relate to differences in cardiac capacity and functioning (Eliason et al 2011). Atlantic salmon Salmo salar or Pacific sockeye salmon Oncorhynchus nerka do not feed during spawning migrations (Doucett et al 1999, Cooke et al 2004. They thereby protect their aerobic scope from being compromised by the cost of food processing.…”

Exceptional aerobic scope and cardiovascular performance of pink salmon (Oncorhynchus gorbuscha) may underlie resilience in a warming climate

“…These species have significant cultural and biological value, and they form the basis of a commercial fishery in British Columbia that can exceed $1 billion annually. However, recent decades have seen a precipitous yet unexplained decline in the abundance of many Pacific salmonid species in the Fraser River watershed (Cooke et al, 2004;Farrell et al, 2008;Welch et al, 2009;Chittenden et al, 2010;Hague et al, 2011).…”

Ionoregulatory changes in different populations of maturing sockeye salmonOncorhynchus nerkaduring ocean and river migration

“…Most populations of sockeye that spawn in the Fraser River watershed (Chilko and Quesnel) enter the river within a week of arriving at the mouth of the estuary. In contrast, late-run sockeye salmon (Harrison and Late Shuswap), named for their late summer arrival, normally congregate in the Fraser River estuary for 3-6 weeks prior to entering freshwater and initiating their upriver migration to natal spawning grounds (Cooke et al, 2004). The stocks we selected also varied in their migration distances in the freshwater of the Fraser River watershed, ranging from less than 120·km (Harrison) to over 700·km (Quesnel).…”