Spatial and Temporal Distribution of Krill Euphausia superba Biomass in the Ross Sea (1989–1990 and 1994)

Abstract

This chapter aims to improve the knowledge of krill populations in the Ross Sea, an area that has received little attention in the past and which has been thought to be krill-deficient. In the early summer 1989–90, two surveys were conducted in ice-free waters with quasistationary environmental conditions. In the late spring 1994, two more surveys were conducted under conditions of complete to partial ice cover. Concurrent with the acoustic surveys, censuses were taken of the birds and mammals. This chapter gives a description of the instruments used and of data-acquisition and data-processing methods. The results indicate that, contrary to prevalent thinking, the Ross Sea is not krill-deficient. Very dense concentrations of Euphausia superba were found in the southern part of the Ross Sea, up to 76°S in latitude, an area presented in the literature as krill-absent. In these areas, density peaks of krill consumers (minke whales, crabeater seals and Adelie penguins) were found. The mean density of E. superba estimated in 1989–90 and 1994 is of the same order of magnitude as that estimated in the Indian and Atlantic sectors, respectively. On the basis of these results, the authors suggest that the large-scale distribution of krill around Antarctica, presented in the literature, should be supplemented by the part of the Ross Sea extending to the north from the latitude of 76°S.