Poleward and equatorward currents in the Pacific Eastern Boundary Current in summer 1995 and 1998 and their relationship to the distribution of euphausiids

Abstract: This paper examines the relationship between poleward and equatorward current patterns and the spatial distribution of euphausiids based on acoustic survey data collected in summer 1995 and 1998 in the California Current Ecosystem. Contiguous poleward (usually an undercurrent) and equatorward near-surface current core areas were identified by applying current velocity and distance thresholds along each survey transect. Both currents were pervasive along the coast, but poleward volume transport in both years was about an order of magnitude greater than the equatorward near-surface current volume transports. The poleward volume transport was higher in 1998 than in 1995, especially north of Cape Blanco. The poleward transport centroid was generally further offshore than the surface transport centroid, and was closer to the slope in 1998 than in 1995. The depth centroid of euphausiid patches was generally shallower than the depth centroid of the poleward volume transport centroids. The onshore–offshore location of euphausiid patches was significantly related to the location of the poleward transport centroids, although not in all regions. The patches were not related to the location of equatorward near-surface transport centroids. Differences in the north–south euphausiid distribution were observed between 1995 and 1998. In 1995, there was a much higher abundance of euphausiids in the region immediately north of Cape Blanco, while in 1998, euphausiid abundance was high throughout the survey area. We hypothesize this difference to be in part a result of differences in current patterns between the 2 years and the manner in which currents interact with euphausiid diel migration. [Copyright &y& Elsevier]