Humpback Whales (Megaptera novaeangliae)

Humpbacks on the Ledge: Humpback whales are most often sighted in shallow waters on the Ledge itself. They seem to feed primarily on schooling herring, but will also feed on krill and, on the southern edge of the Ledge, sand lance. Humpbacks have been sighted on the Ledge throughout the year, but are most abundant from July through November. Using their distinctive tail flukes for identification, CRU scientists have documented some whales (like the animals named Marble, Petrel, Satula, and Upsilon) which are rarely sighted anywhere but Jeffreys Ledge, while many humpbacks will move between the Ledge, Stellwagen Bank, and other feeding areas depending on prey abundance. Size: 40-50 feet (females are slightly larger than males on average). Weight: approximately 30 tons as full grown adults. Distinctive Marks: Flippers longer than any other whale, usually 1/3 the length of the body; a series of wart-like bumps called "tubercules" (actually enlarged sensory hair follicles) on the upper and lower jaw; stocky body; low, knobby dorsal fin which is variable in shape; 25-50 pleats or grooves on the underside of the throat. Diet: Usually small fish, with some krill (shrimp-like animals; their primary diet in the southern hemisphere). Adults consume up to 3,000 pounds per day while on their feeding grounds. Humpbacks, like most baleen whales, are thought to feed only during the 6-9 months of the year they are on their feeding grounds (see below). They fast and live off their fat layer for the winter period while on their breeding grounds, since there is little food available at that time. Distribution: Humpback whales are distributed worldwide, with three major distinct populations: the North Atlantic, North Pacific, and southern oceans. Genetic research has now indicated that these three populations do not interbreed, and have not in thousands of years. Each population shows similar migration patterns, from warm water winter breeding grounds in low latitudes (places like Hawaii, Mexico, or the Caribbean) to colder water summer feeding grounds in higher latitudes (e.g., Alaska, Antarctica, or New England). Populations generally seem to be structured so that whales learn the migration route to a single feeding ground which they return to annually, while feeding "herds" in the same ocean generally mix on their breeding grounds. Life History: Humpbacks are born during the winter at 10-12 feet and approximately 2,000 pounds after a 11 1/2 month gestation. They are typically weaned in the northern hemisphere during the following December or January, although we have two cases of weaning as early as October). During its first year of life the mother seems to lead her calf through a series of locations where it learns to find food. While the calf also learns how to feed on fish during its first year (both through observing the mother, other animals, and practicing), it nurses on a rich milk, gaining up to 60 pounds per day. The father plays no role in parental care. After leaving its mother, the now juvenile whale generally stays in habitats of medium quality (with limited food supplies) for the next several years. Growth seems to occur in two major periods, one during the first year and one at 3-4 years of age. Females may have their first calf as early as five, and as late as ten years of age; six to eight is most common. Females typically have one calf every two to four years, although we have seen a few females calve in consecutive years. Males appear to be physically mature at close to the same age, they probably do not get to breed until much later in life. Expected life span is 40-50 years, perhaps longer. Social Organization: Humpbacks form generally fluid groups on their feeding grounds, which often seem to come together for cooperative feeding. In rare cases pairs of whales may stay together for weeks or months; in even fewer cases, these associations may last over years. Generally, though, the only stable associations are between mothers and calves; other groups split after brief periods of time (30 minutes to 24 hours). Migration probably also takes place in small groups, rather than in a larger aggregation. On the breeding grounds, males work hard to compete for females. In order to do this, males can use one of two strategies. Males sing the famous song of the humpback whale, which is believed to "advertise" the fitness (size and power) of a male. More often, though, males join battles in "rowdy" groups, where a number of males actually physically combat other males for proximity to a female, who is usually found at the center of the group. While mating has never been observed, it is believed that the female chooses one male to mate with in each year she mates, and the pair is together for only a brief period (several days or less). Population Status: Humpbacks were killed extensively from the late 1800's through the first part of the 20th century. Although they were protected in the early 1960's recent revelations from the Soviet Union indicate massive illegal and unreported kills which went on up until 1970 in the southern oceans. Best estimates are that there are now some 8,000 humpbacks in the North Atlantic, perhaps 4,000 in the North Pacific, and some 3-4,000 in the southern oceans. Although these populations are now protected and recovering, they remain at 10%-20% of original estimates. Currently, the largest threats to humpbacks are entanglements in fishing gear, collisions with ship traffic, and pollution of their coastal habitat from human settlements. Other Sites: Link #1    Link #2    Link #3