FORAGING ECOLOGY AND ENERGETICS OF THE HUMPBACK WHALE IN SOUTHEAST ALASKA

Cetaceans, as the most specialized order of mammals, offer an excellent opportunity to examine the adaptation of an animal to an extreme environment. Little is known concerning the behavior or ecology of any of the baleen whales. Fundamental to an understanding of their distributional and behavioral ecology (necessary for management of the stocks and, more generally, the marine ecosystem) is the ability to estimate their resource and energy requirements. In this study the foraging ecology and energetics of humpback whales summering in southeast Alaska (58{dollar}spcirc{dollar}N., 133{dollar}spcirc{dollar}W) were examined.; Humpback whales were followed in a 5.8m inflatable boat for periods of up to 12.5 h. Whales were tracked in their dive with narrow beam 120kHz sonar. Ventilation and dive patterns were found to be highly correlated with depth of dive. Oxygen utilization per dive, and hence energy expenditure, was estimated from calculated tidal volume, oxygen extraction efficiency, and measured ventilation rates. Energy costs of diving increased with depth, most markedly beyond 60m, the estimated aerobic limit of the whales. Dives were restricted to the top 150m and only rarely exceeded 120m.; A remotely operated underwater camera system, consisting of 35mm and video cameras, flood lamps, and maneuvering jets, was constructed to examine and characterize potential prey patches in the water column. In conjunction with sonar, acoustic backscatter intensity was correlated with stereologic analysis of photographic images, allowing visual and acoustic estimates of prey identity, density, and patch structure. A mathematical model predicting optimal foraging tactics was devised based on prey patch value as a function of patch density and relative time and energy costs of capture. Whales foraged in a manner maximizing the gain:cost ratio in keeping with predicted models. Whales inevitably fed upon the shallowest densest patches available.; The distribution and abundance of prey varied by year; theoretically, so too would the whales' net energy gain. The highest percent of calves in the area occurred one year after seasons of abundant, shallow prey. It is postulated that variations in prey value may measurably effect reproductive success in humpback whales.