Interannual changes in body fat condition index of minke whales in the Antarctic

To study whether or not wide-ranging pelagic predators should be affected b y localized changes in prey availability, interannual variability in body f at condition index (assessed from girth measurements) of minke whales Balae noptera acutorostrata was analyzed in relation to their distribution, stoma ch-content mass and sea-ice extent during the austral summer in the Antarct ic Ocean between 130 degrees E and 170 degrees W. The research area compris ed offshore, ice-edge and Ross Sea areas. Of the 3 years (1990/91, 1992/93 and 1994/95) included in the study, 1994/95 was a year of significantly poo r body fat condition compared with the other 2 years. The 1994/95 year was characterized by extensive sea-ice conditions, covering the usually krill-r ich slope region throughout the season. Since minke whales were scarce and their stomach-content mass small in the ice-edge area during 1994/95, food availability in the area during the season was considered to be poor as a r esult of the high sea-ice extent. Antarctic krill Euphausia superba was reg ularly the dominant prey species throughout the survey area, although on th e Ross Sea shelf E. crystallorophias was the codominant prey with E. superb a. The spatial distribution of body size and maturity of E. superba indicat ed apparent unsuitability of the Ross Sea area as a nursery and spawning gr ound for that species. The Ross Sea area was considered to be an area of lo w food supply throughout the study period, considering the lower level of s tomach contents. Paradoxically, this area usually contained numerous minke whales, especially pregnant females. In conclusion, minke whales appear to have been affected by considerable interannual variability in food availabi lity in the ice-edge area, i.e. potentially the most krill-rich area along their migratory route.