Eddies and Jets: Chinook Salmon Catch Distribution in a Dynamic Ocean

Salmon are known to change distribution in response to ocean conditions. Chinook catch off the central Oregon coast is associated with three areas: the continental shelf break; a complex of high-relief cross-shelf bathymetry; and a near-shore area of rocky reefs. Within this area catch locations are highly variable. Bottom features interact with current patterns to generate complex and dynamic oceanographic structures including fronts, eddies, and jets. Catch locations in 2012 and 2014 were largely non-overlapping. In 2012 near 45 degrees N latitude there were two areas of high catch, one onshore and the other offshore. In 2014 there was a single offshore area of high catch rates, but within this area catch moved monthly on a scale of 10 km. Ocean conditions in the two years differed in the position and strength of an offshore jet following the continental shelf break. Preliminary analysis suggests that salmon catch was associated with the near-shore edge of this jet. Establishing a linkage between fish stock distributions and physical oceanography at a fine scale provides insights into the dynamic nature of near-shore ocean habitats. Characterization of habitat preferences adds to our understanding of the ecosystem, and may improve forecasts of distribution for harvest management.