Key Factors Determining the Distribution of Beluga Whales, Delphinapterus leucas (Pallas, 1776), in River Estuaries of Western Kamchatka

Resumo

The results of observations on the distribution of beluga whales, Delphinapterus leucas (Pallas, 1776), in three large rivers of western Kamchatka in the summer and autumn seasons are discussed. In the summer, the number of beluga whales in the Khairyuzova, Belogolovaya, and Moroshechnaya rivers reaches 111–250 individuals. Most of the belugas enter the rivers during the flood tidal phase: the number of animals in the estuaries increases along with the rising water level to the maximum value at spring tide. The belugas do not move upstream out of the estuaries and tend to remain in the zone of mixing riverine and marine waters, where 20 species of fish and three species of invertebrates have been identified. At ebb tide, the belugas leave for the sea; however, during a large run of salmon some individuals remain in the estuaries and continue hunting in deep-water areas. The main issue that causes beluga whales to form summer aggregations in Kamchatkan rivers is the hunt for salmon. The distribution of beluga whales in river estuaries is defined by the dynamics and intensity of salmon spawning runs. The preference of beluga whales for these rivers can be explained by the channel type of their estuaries.