Habitat preferences of female humpback whales Megaptera novaeangliae in the Hawaiian Islands are associated with reproductive status

The main Hawaiian Islands are the primary winter reproductive area for the majority of North Pacific humpback whales Megaptera novaeangliae. Identification photographs of individual whales, including 63 females sighted in at least 2 different years and with at least 1 calf, were collected from waters off the islands of Maui and Hawaii ('Big Island') between 1977 and 1994. Calves formed a significantly larger proportion of the population off Maui than off the Big Island. The overall proportion of calves to all whales identified (crude birth rate) was 0.099 off Maui and 0.061 off the Big Island. Also, considering only females seen in more than 1 year, the number of calves per female per year (calving rate) was 0.71 off Maui and 0.52 off the Big Island. These rates may be inflated somewhat because of the greater likelihood of sighting and identifying females with calf than females without. Females sighted at both Maui and the Big Island in different years were with a calf significantly more often in Maui waters than in Big Island waters. It was concluded that habitat utilisation by females varies between Maui and the Big Island, and appears to depend in part upon reproductive status.