The current status of Antarctic Odontocetes – sperm whales Physeter catodon, killer whales Orcinus orca, long-finned pilot whales Globicephala melaena, hourglass dolphins Lagenorhynchus cruciger and poorly known species of beaked whales (family Ziphiidae)–were studied in Anatarctic waters using data gathered in sighting surveys conducted from 1976/77 to 1987/88. Temporal variation in density demonstrated the different migration patterns by species, especially between sperm whale and killer whale. Spatial distributions during mid-summer demonstrated different peaks of occurrence for each species by latitude that suggest possible segregation between the species. Killer whales occur mainly in the very southernmost areas, sperm whales in the southern half of the study area, beaked whales (mostly southern bottlenose whales Hyperoodon planifrons) ranged over a wide area, and long-finned pilot whales and hourglass dolphins were mainly in the northern regions of Antarctic waters. Several longitudinal peaks of occurrence and apparent distribution gaps were identified for sperm, beaked and killer whales. Abundance estimates for south of the Antarctic Convergence in January are based on line transect theory and were 28 100 animals (coefficient of variation CV 0.18) sperm whales, 599 300 (0.15) beaked whales (mostly southern bottlenose whales), 80 400 (0.15) killer whales, 200 000 (0.35) long-finned pilot whales, and 144 300 (0.17) hourglass dolphins. Based on this, biomass of these species were estimated as 0.77 (sperm whales), 2.70 (beaked whales), 0.32 (killer whales), 0.16 (long-finned pilot whales) and 0.01 (hourglass dolphins) million tonnes. Consumption of food (mostly squid) by the Odontocetes is estimated as 14.4 million tonnes with 67% of the total consumed by beaked whales. Indirect consumption of Antarctic krill through the predation of squid by beaked whales is estimated to be c. 24 million tonnes. This value is similar to the estimate of krill consumption by penguins in the Antarctic (33 million tonnes). Odontocetes, especially southern bottlenose whales, are suggested to have a much greater role in the Antarctic ecosystem than has previously been considered.

ABSTRACT. Although a number of measurements have been made on radiocesium concentrations in aquatic organisms, no clear agreement has been reached on the factors affecting accumulation of these radionuclides. Natural variations in the concentration of the long-lived artificial radionuclide '37Cs in marine organisms and factors affecting variations in marine fishes were investigated through long-term and systematic measurements in coastal waters of Japan from 1984 to 1995. Concentrations of 13' Cs were measured in more than 30 species of crustaceans, cephalopods and teleosts considered representative of the marine biotic community. A clear positive correlation (p < 0.05) was found between mean weight and concentration of 137Cs in 276 fish samples. However, different relationships between 137Cs concentration and weight of fish were observed in different species. Within 16 studied species I3'cs concentration increased with growth for 4 species, while no specific correlation was observed in the remaining species. These different patterns depended on a change of food habits with growth. Analysis of 6066 stomach contents of fish samples together with '37Cs concentrations in the stomach contents demonstrated that 137Cs concentration increased with rising trophic level and that the biomagnification factor (13'cs in p r e d a t~r / '~~C s in prey) was 2.0 (95% confidence interval 1.8 to 2.2). From the yearly change of '37Cs in 24 marine fish species, a mean effectlve environmental half-life of I3'Cs of 13 * 3 yr (range 10 to 17 yr) was calculated.

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Southern minke whales Balaenoptera acutorostrata are genetically separated from Northern Hemisphere minke whales. Seasonal migrations take them from tropical latitudes in winter to high latitudes of the Antarctic in summer. Breeding takes place in warmer waters but llttle is known of breeding areas. Breedmg areas and southbound migrations were studied using sighhng data derived from the Japanese sighting surveys dunng 1976 to 1987. Relatively higher concentrations were observed In the waters mainly around 10" to 20" S in October, the end of the main conception period of this species in the Southern Hemisphere Spatial distribution in tropical and subtropical waters during the latter half of the conception period suggests that there are 2 breeding areas In the eastern and western South Paclflc and 2 others in the eastern and western Indian Ocean. It appears that breeding populations of the southern minke whale are relatively dispersed in open waters while coastal species such as right whales Eubalaena glacialis, humpback whales Megaptera novaeangliae and gray whales Eschrichtius robustus migrate along the shore and congregate in near-shore breeding areas. Latitudinal occurrences by month suggest that southern minke whales moved southward from the breeding areas by October-November, and that most of them had migrated into Antarctic waters by January. They tend to move almost directly south from the breeding areas to feeding areas, and subsequently disperse after arriving at the feeding areas. Southbound migration speeds were estimated to average 20 nautical miles (n miles) d-' in waters north of the subtropical convergence and 40 to 50 n miles d-' in waters south of the convergence.

The relationship between the distribution of minke whales (Balaenoptera acutorostrata) in the Bellingshausen and Amundsen Seas (longitude between 60°W and 120°W), and environmental and physiographic variables (sea‐surface temperature, sea‐ice extension, and sea‐floor‐slope type), was studied to determine whether these environmental and physical factors affect the distribution and density of minke whales. The analysis was based on sightings data obtained from the 1989/90 and 1982/83 IWC/IDCR cruises. The mean sea‐surface temperatures for comparable areas were significantly higher in 1989/90 (2.04°C) than in 1982/83 (1.12°C), and the area where the sea‐surface temperature was greater than 1°C in the 1989/90 study was approximately twice that of the 1982/83 study. Additionally, during the surveys, the extent of the sea ice in 1989/90 was less than that in 1982/83, with the mean ice edge about 92.6 km (50 nautical miles; 1 nautical mile ≈1.852 km) farther south in 1989/90 than in 1982/83. This is consistent with the sea ice extent observed in winter, when the sea ice extent was less in 1989 than in 1982. The distribution of minke whales was substantially different between the two surveys, with the density and abundance of minke whales being greater in 1982/83 than in 1989/90. The warmer sea‐surface temperatures, fewer cold‐water intrusions, and the smaller extent of sea ice in 1989/90 may be related to the difference in distribution of minke whales from 1982/83, possibly owing to the shift in availability of prey.