Breeding areas and southbound migrations of southern minke whales Balaenoptera acutorostrata

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.