Some observations on the feeding activity of Antarctic krill in the Indian Sector of the Antarctic Ocean

Abstract

The BIOMASS FIBEX Cruise of R/V KAIYO MARU in the Indian Sector of the Antarctic Ocean was conducted from 11 November, 1980 to 18 March, 1981. The investigation could be subdivided into three stages on the basis of the area and the duration : Investigation I (11-26 December, 1980; Long. 60-85°E), Investigation II (16-30 January, 1981; Long. 30-55°E) and Investigation III (31 January-6 February, 1981; Long. 60-70°E). Feeding activity of the Antarctic krill, Euphausia superba DANA, was studied regarding the sexual maturation by examining the digestive tract contents. It seemed that feeding of the krill was active two times a day. In Investigation I the active period of feeding was between 00 and 03h and 12 and 15h or between 12 and 18h in both sexes. With the advance of time (Investigation III) the active period of feeding was different between sexes, and the feeding activity varied little in mature female. From the present examination it was difficult to confirm the relation between the population density causing vertical migration and the feeding activity.