The humpback whale (Megaptera novaeangliae) is the baleen whale most frequently seen swimming or feeding close to shore along the southern coast of Alaska. When beginning to dive, animals often lift their flukes (tail) out of the water thereby exposing the pattern of black and white which characterizes the ventral side. This pattern varies with each whale and is used by biologists to identify individual animals. Humpbacks may stay submerged for as long as 30 minutes although most dives do not last longer than 15 minutes. When resting near the surface between dives, whales may blow every few seconds.

General description: Humpback whales are distinguished from other whales by the extremely long flippers which may reach 25 to 30 percent of the length of the entire animal. The animals appear generally dark when viewed from above although the flippers may have varying amounts of white on the dorsal side. The underside of the flippers and tail, and often the sides and ventral surfaces of humpback whales may be partially white. Humpback whales have a small dorsal fin which is often seen when the animal is beginning to dive. Adults may reach a length of 55 feet (16.7 m) although the average adult length for west coast animals taken during the days of whaling was 42 feet (12.7 m) for females and 40.5 feet (12.3 m) for males. Like other baleen whales, adult females at any given age are usually larger than males. The plates of baleen are generally dark in color and number 270 - 400 on each side of the upper jaw.

Distribution and migration: Humpback whales occur throughout the world's oceans but they are not common in arctic waters. Although humpbacks may be seen at any time of year in Alaska, most animals undertake long distance migrations during the fall to temperate or tropical wintering areas where reproduction occurs and the young are born. During spring, the animals migrate back to Alaska where food is abundant. Humpback whales that summer in the north Pacific are from three separate stocks which winter in Mexico, in Hawaii, and in the western Pacific near the Mariana, Bonin, and Ryukyu islands. Whales that summer in Alaska are primarily from the Hawaii stock. Although the length of time needed to make migrations is not well known, one whale that was identified in Alaska was seen 39 days later in Hawaii 2,800 miles (4,500 km) away. When in Alaska, humpback whales tend to concentrate in several specific areas including Southeast Alaska, Prince William Sound, the area near Kodiak and the Barren Islands, the area between the Semidi and Shumagin Islands, and the eastern Aleutian Islands and southern Bering Sea.

Abundance: Before whaling began, approximately 15,000 humpbacks are estimated to have existed in the north Pacific. Humpbacks were subjected to severe harvest pressure during the twentieth century; more than 23,000 animals were taken in the north Pacific before this species was granted protection from whaling in 1966. By that time the north Pacific population may have been reduced to 1,000 animals. Recent studies, including those following the Exxon Valdez oil spill, indicate that more than 500 humpbacks may now be found in Southeast Alaska during summer, and more than 100 humpbacks may be found in Prince William Sound.

Food habits: Humpback whales in Alaska feed principally on herring, other small schooling fish, and on swarms of euphausiids (krill). These whales use a variety of feeding behaviors to catch food including underwater exhalation of columns of bubbles that concentrate prey, feeding in formation, herding of prey, and lunge feeding. Multi-year group association and cooperative feeding between individuals has been observed. Ventral grooves allow the animal's throat to expand greatly and take in large volumes of water which are then forced out across the baleen which retains the food.

Reproduction: Humpback calves are born in tropical waters after a gestation period of approximately 11 to 12 months. Newborn animals average 2 tons in weight, measure approximately 12 feet (3.6 m), and suckle for up to a year. Sexual maturity is reached at 4 to 6 years. Mature females give birth every two or three years although females in Southeast Alaska have been seen with new calves during two or more consecutive summers. Songs produced by males on the wintering grounds appear to be related to courtship. The significance of songs recorded on summering grounds is less well known but some of the calls are believed to be related to feeding activities.

Sources of mortality: Killer whales and humans are the major predators of humpback whales. Sharks may also take some animals. Although not observed in Alaska, humpbacks have died from paralytic shellfish poisoning in New England. Collisions with vessels, entanglement in gillnets, entanglement in seine nets, entanglement in fishing lines, and entanglement in cables from abandoned logging operations have all killed humpbacks in Alaska. A Federal Recovery Plan was formulated for this species in 1991. The intent of this plan is to assist humpback populations to grow and to reoccupy areas where they were historically found.

Text: Steven T. Zimmerman
Illustration: Don McMichael
Revised and reprinted 1994