Biological and environmental covariates of juvenile sockeye salmon distribution and abundance in the southeastern Bering Sea, 2002-2018

Climate change is altering the distribution and abundance of marine species, especially in Arctic and sub-Arctic regions. In the eastern Bering Sea, home of the world's largest run of sockeye salmon (Oncorhynchus nerka), juvenile sockeye salmon abundance has increased and their migration path shifted north with warming, 2002-2018. The reasons for these changes are poorly understood. For these sockeye salmon, we quantify environmental and biological covariate effects within spatio-temporal species distribution models. Spatio-temporally, with respect to juvenile sockeye salmon densities: (1) sea surface temperature had a nonlinear effect, (2) large copepod, Calanus, a minor prey item, had no effect, (3) age-0 pollock (Gadus chalcogrammus), a major prey item during warm years, had a positive linear effect, and (4) juvenile pink salmon (O. gorbuscha) had a positive linear effect. Temporally, annual biomass of juvenile sockeye salmon was nonlinearly related to sea temperature and positively related to age-0 pollock and juvenile pink salmon abundance. Results indicate that sockeye salmon distributed with and increased in abundance with increases in prey, and reached a threshold for optimal temperatures in the eastern Bering Sea. Changes in population dynamics and distribution of sockeye salmon in response to environmental variability have potential implications for projecting specific future food securities and management of fisheries in Arctic waters. This manuscript describes changes in the distribution and abundance of juvenile sockeye salmon from Bristol Bay, the world's largest run of sockeye salmon, in relation to spatio-temporal and temporal changes in prey, competitors, and temperature. Spatio-temporally varying densities of juvenile sockeye salmon varied with sea temperature, age-0 pollock and juvenile pink salmon, but not Calanus copepods. Temporally, increases in annual biomass of juvenile sockeye salmon corresponded nonlinearly with warming, positively with age-0 pollock (a highly abundant prey during warm years), positively with juvenile pink salmon (a potential competitor), but did not correspond with large copepods (smaller prey).image