The more we learn about humpback whales as we travel Alaska, the more amazing we find their behavior. Humpback whales can be individually recognized from the pattern of black and white on the underside of the flukes, seen as the whales dive, and this has been the key to the study of their populations and behavior. At one time, we thought that there were a few hundred humpbacks in Alaskan waters. Now, by cataloging individuals we’ve spotted during our Alaskan cruises, we know the number to be in the thousands and increasing. That is very good news.
Humpback whales reach 50 feet and about 40 tons. Their most distinctive feature is the pair of enormously long pectoral fins, which can be one-third the length of the whale.
The humpback whales of Southeast Alaska that we see on our Alaska cruise spend their winter around Hawaii. Basically, Alaska is for feeding and Hawaii is for breeding. When the whales make the long (about 2,700 miles) northbound journey in spring their reserves of body fat are depleted. They have fed little, if at all, since leaving Alaska the previous fall. Females that gave birth in Hawaii swim in company with their new calf. Once they reach the food-rich Alaskan waters they have the capacity for hyperphagia - adaptive overeating. As baleen whales, they feed using fringed plates that hang down in series from their upper jaw, 270-400 per side. They engulf large mouthfuls of seawater and then force the water out through the baleen, trapping the prey. Humpbacks feed on krill and on small schooling fish like herring. They are flexible in their feeding behavior and their choice of prey. Most frequently, individuals feed alone, but sometimes a group assembles to engage in the most remarkable behavior of cooperative bubble-net feeding. There may be as few as four or five, or there may be over twenty in a cooperating group. This highly coordinated behavior makes use of a tool: a net of bubbles released by one of the whales to corral a school of fish. Briefly, the whales of a group dive in short succession. Under the water, they find a school of fish, confine it within the bubble net, and flash the white underside of their long flippers to further concentrate the fish. At a vocal signal given by one of the whales, all rise through the bubble net and burst onto the surface, their huge mouths agape, engulfing water and fish together. We have learned that membership in a cooperative group is stable, only some of Alaska's humpback whales engage in this behavior, and these do not always feed in this manner. The whales often separate and feed individually, presumably when conditions are not right for cooperative feeding. We have much to learn on future Alaska tours about the remarkable behavior of humpback whales.
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