Hydrobiological Features of the Shantar Aquatic Area in Relation to Summer Grazing of Bowhead Whales of the Okhotsk Population.

Abstract—The bay waters of the Sea of Okhotsk near the Shantar Islands are the most important summer grazing areas for bowhead whales (Balaena mysticetus) of the Okhotsk population. A hydrobiological survey during the period from July 12–28th, 2016, demonstrated that waters around the Shantar archipelago are characterized by high concentrations of humic substance supplied by the peat-laden banks of rivers flowing into the bays. The average chlorophyll concentrations in bottom waters of Uda and Academy bays were 1.1 and 4.3 mg/m3, respectively. Uda and Academy bays are mainly considered heterotrophic and autotrophic basins, respectively. The measured zooplankton biomass in Uda Bay ranged from 9.5 to 2513 mg/m3, averaging 736 mg/m3; the corresponding characteristics in Academy Bay were 0.38 to 3620 mg/m3, averaging 458 mg/m3. In the Shantar water area, copepods of the species Calanus glacialis were the dominant contributor in terms of zooplankton biomass and species abundance. During early summer, nine bowhead whales were sighted south off Feklistov Island and lone whales were recorded in the North Strait and at the mouth of Nikolai Bay. The low density of polar whales in the Shantar water area in early summer may be due to the low zooplankton biomass after spring bloom and the last spawning. [ABSTRACT FROM AUTHOR]