Understanding the mechanisms of population depression for endangered Cultus Lake Sockeye Salmon to inform fisheries management

The Fraser River watershed produces the most abundant bilateral (US and Canada) Sockeye Salmon (Oncorhynchus nerka) fisheries opportunities of any drainage in British Columbia, contributing significantly to commercial, recreational, and First Nations’ interests. Within the watershed, variations amongst populations in run-timing, abundance trends (i.e. cyclical dominance), and other life history traits, evoke a very complex fishery management framework. As Fraser River Sockeye Salmon harvests are managed in a mixed-stock fisheries context (common migration run-timings), less abundant conservation units (CU) can have disproportionate influences on aggregate fishery exploitation potentials.

The Cultus Lake Sockeye Salmon CU is a critically-endangered Fraser River population exhibiting extremely depressed abundances (COSEWIC 2003; DFO Stock Assessment data, unpublished). Cultus Lake Sockeye Salmon are part of the Fraser River Late Run timing group, co-migrating with abundant CU’s, such as the Shuswap Complex CU, which has experienced record escapements in recent years (dominant line). Determination of the ultimate mechanism(s) of influence on survival is critically important to engage informed habitat and fisheries management that succeeds in rebuilding this stock, and alleviating constraints on targeting other Late-Run CUs in the Fraser River mixed stock fishery.

A genomic tool called the ‘salmon FitChip’ has been recently developed by the DFO Molecular Genetics Laboratory to identify specific stressors (e.g. thermal, hypoxia, osmotic and general stress), and diseases (infectious agents, viral disease, inflammation, immune stimulation) in Pacific Salmon (Oncorhynchus spp.) that is based on targeted host response profiling of gill tissue. Gill is an ideal tissue to monitor environmental responses due to its direct contact with water. The chip is populated with biomarker panels that are predictive of the presence of specific stressors, which have been validated in a series of control challenge studies. To predict the presence of a specific stressor requires only 6-12 co-expressed biomarkers (Miller et al. 2017). Within our biomarker panel, we will also include previously validated assays to a range of freshwater infective agents (viruses, bacteria and fungal and protozoan parasites) (Miller et al. 2016) detected in Fraser River Sockeye Salmon in previous years. This is the first tool of its kind to enable the simultaneous assessment of multiple stressor and disease influences on salmonids, or any other species for that matter.

We propose to pair this new genomic tool with our habitat and fish condition information in Cultus Lake (and Chilliwack Lake as a reference) to assess fish stress responses to these potential drivers of poor freshwater survival. Identifying the underlying causes of this early life-stage mortality in nursery habitats will actively inform habitat and fisheries management on remedial actions to improve Cultus Sockeye survival, with the goal of alleviating future constraints on the broader Fraser late-run Sockeye fisheries.