Results of PINRO ecosystem research in the irminger sea at the beginning of XXI century

Abstract

The long-term observations in the World Ocean waters have shown, that the biological cycles of fish are closely connected to the natural cycles (hydrological) in the sea and depend on factors forming them (Beklemishev, 1969). The occurrence of some fish species in the areas with certain environmental conditions allowed us to consider the possibility of divisioning the ocean by biocenoses (Vinogradova, Grusov, 1990). The Irminger Sea is ecosystem in which among the commercial fish species the most abundant population of S. mentella prevails. The structure of the ichthyofauna of the sea and farther south areas adjoining to the northern part of the Mid-Atlantic Ridge has been studied quite sufficiently, however the data on structure and distribution of ichthyocenoses practically are absent. In May-June 2003, during the International Trawl-Acoustic Survey for deep-water redfish stock estimation, for the first time full assessment of all the fish species from pelagic trawl catches was executed. It has enabled considering the structure of the Irminger Sea ichthyocenosis and its changes in respect of both depth and space. During the survey, in the catches, 89 fish species related to 37 families of 14 orders have been found. The quantity of species in the upper 500 m layer was somewhat less than in deeper layers. The greatest numbers of species were related to orders Osmeriformes, Stomiiformes, Myctophiformes and Lophiiformes. The results of researches have shown the presence of juvenile roundnose grenadier at the age of to 3 years in the pelagic layer of the Irminger Sea, and also in the bottom layers on the western slope of Iceland. Spatial distribution of the most abundant species of plankton and nekton which were the basic components in the food supply of deep-water redfish and other fish species was investigated in details. Studying the specific composition of the ichthyocenosis in the Irminger Sea has permitted us to estimate the relative abundance and ratio of various fish species in water coloumn, to reveal the basic features of biology of insufficiently studied fish species, to find out the penetration of warm-loving species of fish from subtropical region into this area. The oceanographic researches which had been carried out during the survey, allowed us to obtain the new data on the living conditions of commercial and non-target fish species. The observations of mammals, which were being executed synchronously by two research vessels (from Russia and Iceland), have allowed to establish the fact of wide summer distribution of the big groups of both cetaceans and dolphins in the sea area and to estimate the increase in their abundance as compared with the period of 1985–1995. The materials from PINRO researches within the last decade have shown significant changes in the ecosystem of the Irminger Sea, one of the reasons of which, in opinion of authors, was long warming of waters in the wide area of the sea which has been observed during the last 10 years.