An analysis of early change in the blubber thickness of minke whales as an indicator of krill availability

Data on blubber thickness measured on 26,751 minke whales caught in the IWC Areas III and IV (0-130 E) by Japanese expeditions from 1971/72 to 1984/85 seasons were analysed. Statistically significant relation were detected between blubber thickness and body length in both mature males and pregnant females. Relation between thickness and foetus length for the latter was also detected. After adjustment for these factors, considerable yearly variations were shown in the thickness in December, in which 12 cases were detected significant out of 24 pairs of successive year comparison. Estimates were obtained for seven years for increment between December and February with a fair agreement between the sexes. Comparison based on the difference between the thickness in December in successive years was proved valid, by which index of krill availability were also esitmated. These two series of estimates of indices were summarized and evaluated. Possible process was discussed to detemine blubber thickness and it was suggested that this parameter is useful to monitor krill availability in the wider geographical range.