Return movement of a humpback whale between the Antarctic Peninsula and American Samoa: a seasonal migration record

Abstract

Humpback whales Megaptera novaeangliae are seasonal migrants that mate and calve at low latitudes and feed at mid- to high latitudes. Connections between most Southern Hemisphere breeding and feeding areas are not well understood, but are critical for assessing stock structure and human impacts. Photo-identification was performed to identify the feeding grounds of an Endangered sub-population that breeds in the central South Pacific Ocean (CSP). Identification photographs were obtained from 159 ind. at American Samoa and compared to 3508 Southern Hemisphere humpback whales in the Antarctic Humpback Whale Catalogue (AHWC), including 1352 from Antarctic feeding grounds. Two individuals from American Samoa were seen on 3 occasions at the Antarctic Peninsula. This is the first known feeding site for American Samoa and one of few reliably identified for the CSP. AHWC #2950 was confirmed to have undertaken a round-trip movement of no less than 18 840 km, spanning 108 longitudinal degrees. This represents the largest mammalian migration known to date and a departure from historical assumptions about CSP migratory patterns. The frequency, causes, and fitness implications of such movements have yet to be determined. However, distance is the only known extrinsic barrier to humpback whale movement within oceans, and so maximum individual range is 1 factor potentially affecting population exchange and colonization of new habitats. The movement documented here may place this Endangered sub-population at risk if conservation efforts are relaxed in unidentified parts of its range. Yet, the ability of humpback whales to undertake such extensive movements may have also contributed to the apparent recovery of some populations versus other historically exploited whale species.