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The spatial distribution of Antarctic minke whales in the Ross Sea with relation to spatial distributions of their prey – krill – was investigated in this study using generalized additive models (GAMs). Spatial distributions of two species of krill (ice and Antarctic krill) were estimated by GAMs. Three abiotic factors – distance from the continental shelf break (800 m isobaths), the mean temperature and salinity from the surface to 200 m (MTEM‐200 and MSAL‐200), and latitude and longitude – were used as covariates for models of krill. Estimated spatial distributions of krill were then used with other covariates to model the spatial distribution of Antarctic minke whales. In the selected model of Antarctic minke whales, Antarctic krill were more influential than ice krill. The number of Antarctic minke whales increased as the density of Antarctic krill increased to around 1.5 g m−2. Beyond that, the number of Antarctic minke whales decreased as the density of Antarctic krill increased. High densities of the Antarctic minke whales were estimated along the sea ice edge in the eastern part of the Ross Sea. Specifically, the densities were high in the north of the continental shelf break where low MTEM‐200 and MSAL‐200 and intermediate densities of Antarctic krill were observed. Further data collection is needed to investigate interannual variations and trends in their relationship. The results show that the spatial distribution of Antarctic minke whales is a function of longitude, distance from the shelf break, oceanographic condition (temperature and salinity), and densities of ice and Antarctic krill.

Sighting survey data from the Japanese Whale Research Program under Special Permit in the Antarctic (JARPA) are analysed to obtain abundanceestimates for humpback whales (Megaptera novaeangliae) south of 60°S. The surveys were conducted during the 1989/90–2004/05 austral summerseasons (mainly in January and February); the survey areas alternated between Area IV (70°E–130°E) and Area V (130°E to 170°W) each year.Primary sighting effort totalled 293,811 n.miles over 6,188 days. Abundance estimates are obtained using standard line transect analysis methodsand the program DISTANCE. Estimated densities of humpback whales were highest east of the Kerguelen Plateau (80°E–120°E). Abundanceestimates for Area IV range from 2,747 (CV = 0.153) in 1993/94 to 31,134 (CV = 0.123) in 2001/02, while those for Area V range from 602 (CV= 0.343) in 1990/91 to 9,342 (CV = 0.337) in 2004/05. The estimates are similar to those obtained from the International Whaling Commission’sIDCR-SOWER surveys, which were conducted in Area IV (in 1978/79, 1988/89 and 1998/99) and in Area V (in 1980/81, 1991/92 and 2001/02–2003/04). Estimated annual rates of increase for Area IV (16.4%; 95% CI = 9.5–23.3%) and Area V (12.1%; 95% CI = 1.7–22.6%) are also similarto those obtained from the IDCR-SOWER surveys. The total abundance in Areas IV and V based on the most recent JARPA surveys (2003/04 and2004/05 combined) is 37,125 (95% CI = 21,349–64,558); the confidence interval incorporates estimated additional variance. Results of severalsensitivity tests are presented that suggest that estimates of abundance and trends are not appreciably affected by factors such as different approachesto deal with survey coverage (which in some cases was poor or included gaps). Changes in the order in which survey strata were covered andpotential effects are investigated using a nested GLM approach; a QAIC model selection criterion suggests a preference for not attempting to adjustfor such changes. Under various sensitivity approaches, the point estimates of increase rates are not greatly affected for Area IV. Although theydrop by typically a half for most approaches for Area V, they nevertheless remain within the confidence limits of the base case estimate of 12.1%per year (95% CI = 1.7–22.6%). The presented results thus suggest that the estimated abundance of humpback whales in Area IV has increasedrapidly. Although there is also an increase indicated for Area V, it is neither as rapid nor as precisely estimated. Taking these results together withthe similar rates of increase estimated from coastal surveys off western and eastern Australia for Breeding Stocks D and E respectively, and givendemographic limitations on the increase rates possible for closed populations of humpback whales, the hypothesis is advanced that whales fromBreeding Stock E may have shifted their feeding distribution westward as their numbers have increased, perhaps to take advantage of the higherdensities of krill to be found to the west.

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