FEEDING OF THE FISH OF BLAGODATNOE LAKE (ITURUP Island, KURIL ISLANDS) IN SUMMER

Abstract

The feeding of mass fi sh species is described according to the data of ichthyological samples in June- August 2001 from Blagodatnoye Lake (Iturup Island, Kuril Islands):whitebaits of Oncorhynchus keta, Hypomesus nipponensis, Pungitius spp., Gasterosteus nipponicus, Salvelinus malma curilus, S. leucomaenis, Cottus amblystomopsis, Gymnogobius urotaenia and Tridentiger brevispinis. Whitebaits of Oncorhynchus keta, Pungitius spp. and Gasterosteus nipponicus formed the basis of catches in terms of abundance and biomass in the coastal zone of the lake. Hypomesus nipponensis is typical of shallow lake waters and has been constantly observed in the coastal area. Four ecological groups of fi sh are distinguished by the type of food. The fi rst group includes whitebaits of Oncorhynchus keta only, which are the most separated from other species in terms of the ecological spectrum of feeding. The basis of the diet of whitebaits of chum salmon (85 %) is non-aquatic insects consumed from the surface of the water. Salvelinus malma curilus and Hypomesus nipponensis exerted the greatest competitive pressure on juvenile salmon, 11 and 10 % of their diet also consisted of extra- aquatic insects, respectively. Hypomesus nipponensis is a plankto- benthophage and belongs to the second group. The basis of the ecological food spectrum of this species was formed by zooplankton (43 %) and zoobenthos (30 %). A signifi cant contribution was also characterized by fi sh eggs (17 %). The third group includes the Japanese three- spined sticklebacks, the main food of which is fi sh eggs (59 %) and zoobenthos (34 %). All other fi sh species are included in a single group of predominant benthophages. The contribution of zoobenthos in the ecological spectrum of nutrition of these fi sh varied from 57.4 % in Gymnogobius urotaenia to 100 % in Tridentiger brevispinis.