Determination of Boreal and Subtropical Zooplankton Energetic Quality in the Northern California Current and Its Implications for Higher Trophic Level Feeding Dynamics

Within the Northern California Current, a transition occurs in the zooplankton community structure, as subtropical zooplankton species common off California are replaced by boreal ones typical to Oregon and Washington’s much colder waters. In this project, scientists will collect zooplankton samples (copepod and euphausiid species) every month for a year along an established transect off Trinidad Head in Humboldt County (latitude 41°). Some sampling will also be conducted in a transect three degrees north in Newport, Oregon. Both transect lines are surveyed regularly as part of the Pacific Coast Ocean Observing System, which was established, in large part, to collect environmental data for salmon fisheries management. The dominant zooplankton species collected during the cruises will be analyzed for their lipid and protein content to assess food quality for juvenile salmon and other animals. The hypothesis is that boreal zooplankton will have a higher energy content than that of the subtropical species and that this will translate into higher survival rates for juvenile salmon feeding in boreal-zooplanktondominated waters. A year-long time series of prey energy content will be constructed for the Trinidad Head survey line, and there will be analyses of seasonal changes in energy content and its potential relationship to wintertime upwelling, which for salmon may be critical for early atsea survival. Results will be used to help assess the applicability of a “Northern Copepod Index” (used successfully to forecast salmon returns one to two years in the future in Oregon and Washington) to salmon fisheries in Northern California.