Relation of Feeding in Juvenile Chum Salmon (Oncorhynchus keta) and Pink Salmon (O-gorbuscha) to Abundance of Zooplankton in Coastal Waters of the Prostor Bay (Iturup Island)

摘要

The paper characterizes feeding of juvenile chum salmon Oncorhynchus keta and pink salmon O.gorbuscha during the fattening period in July 2013-2015 within the coastal zone of 0.5-1.5 km from the shores. The study revealed that both species exhibited diverse feeding in the pelagial, but older Neocalanus spp. and Pseudocalanus spp. copepodites were the main food items determining adequate covering of the fish demands for food. These invertebrates formed 78% of the total zooplankton biomass in the upper water layer (0-10 m). In 2013 and 2014, all juvenile fish specimens were feeding and were fed satisfactory. In 2015, feeding intensity of the juvenile fish was weaker and more than 1/3 of the fish were starving by the end of July. On average for three observation years, chum and pink salmons were feeding at the narrow shallows almost twofold better than over the wide shallows. Specific features of the fish feeding revealed in the present study are in agreement with the interannual and local fluctuations of the zooplankton abundance.