Regional and local effects drive changes in spawning stream occupancy in a sockeye salmon metapopulation

Abstract

There is a need to explicitly consider metapopulation dynamics in the development of conservation strategies for spatially structured populations. We examined the spatial dynamics of sockeye salmon (Oncorhynchus nerka) that spawn in 36 streams of the Stuart River watershed in British Columbia, Canada, using a 69-year record of spawner abundance and a demographically based Bayesian dynamic occupancy model. We identified a set of 12 streams with good habitat conditions that were occupied >90% of years despite large year-to-year changes in abundance. Over 85% of spawners were concentrated in these streams. Many other streams with poorer habitat had small populations that were not persistent over time and were periodically recolonized by dispersers from other streams. Although it is often assumed population diversity and resiliency is maximized when all available habitats are used, for this salmon metapopulation, resiliency is due to the core streams of higher habitat quality. Currently, other streams make only small contributions to population abundance; however, some may have conservation value if their habitats become more suitable for spawning in the future.