Summary of humpback whale research at American Samoa, 2003-2005

Robbins, Jooke; Mattila, David

American Samoa is a poorly understood wintering site for humpback whales in Oceania. Here we describe the results of photo-identification and biopsy sampling performed on 27 days between September 18 and October 7, 2003-2005. Work was performed from a 7-meter vessel working in the coastal waters of Tutuila, the primary island of American Samoa. The detection rate was consistently low, averaging 5.5 humpback whales per day in all three years. The most common sightings were of singletons (31%) and paired whales (23%). Four singletons were confirmed to be singing, but not all were checked for that behavior. Mother-calf pairs were alone (15%) or escorted by a single large whale (12%). One mother was observed on two occasions prior to her first sighting with a calf, making it likely that the birth took place in American Samoa waters. Competititve activity was observed in 9% of groups sighted, despite the low densities observed. Competitive groups were small, ranging from only 3-6 whales (ave=3.8). Overall, the behaviors observed were consistent with those at other low-density breeding grounds, although apparent feeding was also noted on one occasion. Of 50 individuals with sufficient photo-documentation, none were re-sighted there between years. However, 11% (n=4) of those photo-identified prior to 2005 were successfully matched to other breeding sites in Oceania, including the Cook Islands, Tonga and Moorea (French Polynesia). Together, these results indicate that American Samoa is part of a widely dispersed breeding population.

Summary of humpback whale research at American Samoa, 2003-2005

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