Известия ТИНРО (Sep 2017)
Feeding and trophic relations of mass fish species in the Kuril waters of the Pacific Ocean
Abstract
Feeding conditions of the main commercial fish species are assessed and their feeding relationships are considered on the materials collected aboard RV Professor Levanidov and RV TINRO in the Pacific waters at Kuril Islands in July-August of 2015 and 2016 in the surveys targeted on evaluation of the subtropical species migrations, as Scomber japonicus, Scomber australasicus, Sardinops melanostictus , and Todatodes pacificus , as well as pre-anadromous migrations of salmons Oncorhynchus gorbusha and Oncorhynchus keta . Copepods, euphausiids, and hyperiids dominated in the diet of subtropical species, with exception of Scomber japonicus and Scomber australasicus with fish as a significant part of the diet and Sardinops melanostictus with phytoplankton in the diet. In the salmons diet, copepods, euphausiids, hyperiids, and pteropods prevailed for pink salmon and euphausiids, pteropods, hyperiids, and medusas for chum salmon. Daily and monthly rations were calculated for fish species and their ratio with the stock of large-sized zooplankton was determined. The main consumers of zooplankton were Scomber japonicus (49 % of total consumption in 2016) and Sardinops melanostictus (40 %) and the main consumers of nekton - Scomber japonicus , too (86 % of total consumption in 2016) and Scomber australasicus (13 %). Salmons consumed no more than 1 % in sum. In 2015, Scomber japonicus also was the main consumer (73-71 % of the total consumption of zooplankton and nekton) and salmons’ consumption was even lower. The stock of zooplankton, being in 18 times larger than the fish biomass, provided full feeding demand of the consumers. The stocks of the preferable preys, as euphausiids, copepods, and amphipods, exceeded their consumption in 15-25 times in 2016, though slight deficit of euphausiids was observed in 2015, compensated by high abundance of copepods, hyperiids, medusas and small-sized nekton.
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