Features of functioning for plankton communities and feeding for pacific salmon in the deep-water areas of Bering and Okhotsk Seas (comparative analysis)

Species composition, functional structure and production of plankton communities is considered on the long-term data collected in 1986–2022 together with diet and ration for two species of pacific salmon ( Oncorhynchus gorbuscha and Oncorhynchus keta ) during their feeding in the deep waters of Bering Sea and Okhotsk Sea. Significant regional differences are found for the macroplankton. The functioning of plankton communities in the Okhotsk Sea is more efficient for maintenance of the salmon feeding. Both salmon species consume mainly amphipods, copepods and arrowworms. Bathymetric distribution of plankton and seasonal succession of the plankton communities are different between the seas, so the feeding intensity, daily ration and species composition of diet vary considerably between them, as well. However, high production of large-sized planktonic predators and active transport of zooplankton from outside areas are noted for both regions that provides a stable food base for salmon even in cases when the total production of zooplankton community is low there. The results obtained are important for understanding the feeding abilities for salmon species and the mechanisms of their year-classes yield formation as a basis for the stocks management.