Changes over a ten-year interval in the distribution and relative abundance of humpback whales (Megaptera novaeangliae) wintering in Hawaiian waters

Aerial surveys of the wintering population of humpback whales (Megaptera novaeangliae) were performed during the 1990 season (Jan–Apr) in the waters adjoining the major Hawaiian Islands using methods consistent with those used in earlier surveys (1977–80). Analysis of these data showed significant increases in both calves and total whales across the intervening period of ten years. Comparisons of number of whales and calves seen on peak flight dates across the five years (1977–80 and 1990) showed significant differences, with numbers of whales and numbers of calves for 1990 revealing the greatest departures from expected frequency. Comparisons of overall encounter rates for both calves (calves/km) and total whales (whales/km) showed significant differences across years, with 1990 rates significantly higher than all previous years. When encounter rates for total whales were compared across years within each of the five major regions (Big Island, Four Island, Penguin Bank, Oahu, and Kauai/Niihau regions), there was a general trend of greater increases moving northwest through the island chain. Together these data suggest that the wintering population may be ‘spilling over’ from previously preferred habitat (Four Island and Penguin Bank regions) and offer supportive evidence that this endangered population may be recovering.