Environmental conditions and compositions of plankton and nekton in the epipelagic zone of the northwestern Pacific Ocean in summer 2009, the year of the largest spawning migration of pink and Chum Salmon

Abstract

The distribution of temperature, salinity, phytoplankton, zooplankton, and nekton, including Pink Salmon and Chum Salmon, is analyzed based on the data from a complex survey conducted in the upper epipelagic zone of the northwestern Pacific Ocean in June–July 2009. An estimate of water transfer, plankton biomass (by size fractions and taxonomic groups), and biomass and abundance of nekton is made. The water circulation pattern was notable for the “compressed” state of the Western Subarctic Gyre. Copepods predominated in zooplankton (60.8% biomass), and Pacific Salmon dominated in the nekton. The ratio of the plankton biomass to the nekton biomass in various biostatistical areas varied from 23.9 to 195.1 (mean 46.7). It was found that the nekton biomass in the area of the spreading subarctic waters reaches its maximum in the summer months and that in the area of subtropical waters reaches its maximum in the fall. In the upper 30-meter layer, the biomass of fish and squid rose during the night to 2.92 million tons, or 1.6 times as much, due to mesopelagic migrants. The nekton communities of the upper epipelagic of the northwestern Pacific Ocean functioned normally, providing a high level of biological and fish productivity.