The food supply for nekton in the epipelagic layer of Pacific waters at the Kuril Islands in the summer seasons of the 2000s

Abstract

Based on data collected during the TINRO-Center expeditions to the Pacific waters off the Kuril Islands and adjacent waters in 2004–2012, the composition and abundance of forage resources of the epipelagic zone are considered, the trophic relationships of nekton are analyzed, the amounts of forage base consumption are calculated, and the food supply for nekton is estimated. It is shown that the significant interannual dynamics of the forage base abundance in the studied area are determined by the dynamics of the zooplankton and, to a lesser extent, the micronekton biomass. In spite of the abundance dynamics and the unevenness of the spatial distribution, the resulting overall stock of zooplankton and micronekton in the considered waters is believed to be rather substantial, from 62 to 158 million tons in the epipelagic layer of the Pacific waters off the Kuril Islands and from 41 to 75 million tons in open offshore waters in various years. The overall consumption of forage resources by nekton varied between years from 1.8 to 9.8% of zooplankton stock; the consumption reached 14.0% only in 2004, at a high abundance of fish and squid and a low stock of the forage base. A comparison of the values of nekton abundance, forage reserve, and volumes of its consumption showed that a decline in the characteristics of the food supply in waters off the Kuril Islands took place only in 2004, 2007, and 2011, whereas in open waters it occurred only in 2009. However there were no significant variations in the quality and intensity of feeding in nekton within these years. In general, significant pressure on forage resources from nekton consumers was not observed in this area in the early 2000s. The resulting overall stock of forage zooplankton and micronekton completely met the food demands of the pelagic nekton, which serves as evidence of a significant carrying capacity of the epipelagic layer in the studied waters, both for its permanent and temporary inhabitants.