SICB Division of Ecology and Evolution (DEE)

DEE Researchers Database Entry

Steven Cooke

A mechanistic approach to understanding mortality of upriver migrating Pacific salmon
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. 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. Our research efforts focus on moving beyond the documentation of current patterns to understanding the mechanisms responsible for them. By understanding the mechanistic basis for patterns in mortality through careful experimentation and observation, we intend to provide managers with in-season management direction for both the late-run sockeye salmon. To date, our efforts have included both large-scale field experiment using telemetry and controlled laboratory experiments. The most promising approach for understanding mortality is to link individual behaviour and fate with physiological and energetic characteristics. To do this, we implant fish with telemetry transmitters and then obtain non-lethal biopsies (e.g., blood, gill, energy) from the same individuals. Using this approach we are developing a mechanistic understanding of the factors associated with mortality and abnormal migration behaviour. For more information see