Science for community fisheries: Population assessment and climate impact monitoring for Heiltsuk-led salmon stewardship

Small scale fisheries support the livelihoods of more than 20 million people and provide food security for millions more around the world, yet science has been slow to embrace the challenge of managing these fisheries. Salmon are foundational for the ecosystems and economies of coastal British Columbia, supporting food, social and ceremonial (FSC) fisheries for 196 First Nations. Despite their cultural and ecological importance, and their vulnerability to ongoing anthropogenic change, we lack the data necessary for management and conservation of wild salmon in much of BC, particularly the remote north and central coast (NCC). Juvenile sockeye rear in lakes for one or two years, so population sizes are often limited by the size and productivity of rearing lakes. Using limnological data collected by Fisheries and Oceans Canada, we built a landscape model of sockeye lake productivity and predicted population capacity for 157 lakes on the NCC. We used these predictions of capacity as priors in a hierarchical-Bayesian stock-recruit model, to estimate productivity, capacity, and conservation benchmarks for 70 sockeye populations. Sockeye are particularly vulnerable to changes in climate, with elevated rates of pre-spawn mortality among migrating adult sockeye at high temperature. Working with the Heiltsuk First Nation, QQs Projects Society, and the Hakai Institute, we established a community-based population monitoring program using a traditional-style salmon weir to capture and tag fish for mark-recapture and telemetry-based estimates of annual population size and temperature-mediated mortality among migrating adult sockeye in the Koeye River. We found rapid declines in survival to spawning when temperatures exceeded 15 °C. Furthermore, river entry measured by the number of fish tagged each day, ceased when the river level dropped below 0.4 m. When water levels are low, migrating sockeye may experience prolonged delays in marine waters, increasing vulnerability to fisheries and predators. Climate impacts on coastal sockeye may therefore be driven by the dual effects of warming temperature and low-water delays. This work will support the development of a Heiltsuk sockeye management plan, establishing management goals and conservation strategies across a territory spanning 15,000 km2 and more than 20 sockeye populations on the NCC.