Humpback whales, Megaptera novaeangliae, live in polar and tropical waters, particularly those of the Atlantic, Arctic, and Pacific Oceans. Their range also includes the waters of the Bering Sea and the waters surrounding Antarctica.
The habitat of humpback whales consists of polar to tropical waters, including the waters of the Artic, Atlantic, and Pacific Oceans, as well as the waters surrounding Antartica and the Bering Strait. During migration, they are found in coastal and deep oceanic waters. Generally, they do not come into coastal waters until they reach the lattitudes of Long Island, New York, and Cape Cod, Massachessetts.
Humpbacks are divided into several populations. These are for the most part isolated, but with a little interchange in some cases. There are two stocks in the north Atlantic Ocean and two in the north Pacific. There are also seven isolated stocks in the southern hemisphere.
The cerebellum of humpback whales constitutes about 20% of the total weight of the brain; the brain does not differ much from those of other mysticete whales.
The olfactory organs of humpback whales are greatly reduced and it is doubtful whether they have a sense of smell at all. Their eyes are small and adapted to withstand water pressure. Their external auditory passages are narrow, leading to a minute hole on the head not far behind the eye.
Humpback females are larger than males. They are one of the few species of mammals for which this is true.
The most distictive external features of humpbacks are the flipper size and form, fluke coloration and shape, and dorsal fin shape. Flippers are quite long and can be almost a third of the body length. They are largely white and have knobs on the leading edge. The butterfly-shaped tail flukes bear individually distinctive patterns of gray and white, and have a scalloped trailing edge. The dorsal fin can be a small triangle or sharply falcate, and often has a stepped or humped shape; this is one source of the name "humpback."
There are 14 to 35 ventral pleats or grooves.
Humpbacks have the greatest relative blubber thickness for their size of any rorqual. Megaptera novaeangliae is second only to blue whales in absolute thickness of blubber. Blubber thickness varies at different times of the year, as well as with age and physiological condition.
Baleen plates are usually all black with blackish bristles.
Humpbacks appear to possess a polygynous/polygamous mating system, with males competing aggressively for access to oestrous females.
The reproductive habits of humpback whales are typically mammalian. The breeding season is during the winter, and breeding takes place in tropical waters.
There are few actual observations of copulation in this species. The male and the female first swim in a line; they then engage in rolling, flipping, and tail fluking. Next, both dive and then surface vertically, with ventral surfaces "in close contact." They emerge from the water to a point below their flippers. They then fall back onto the surface of the water together. The gestation period lasts 11 to 11.5 months. During that time the embryo grows approximately 17 to 35 cm per month.
Sexual maturity is usually reached between 4 to 5 years. In males, the length of the penis can be an indication of sexual maturity. However, in some cases, puberty may proceed sexual maturity by one year. In sexually mature males, the weight of the testes and the rate of spermatogenesis increase during the breeding season, coinciding with the ovulation of the females. In the females, after sexual maturity is reached, ovary weight remains fairly constant. As ovulation approaches, "resting" Graafian follicles on the surface of the ovaries enlarge. There generally is only one ovulation per breeding season.
Breeding usually takes place once every two years, but it may occur twice every three years. In the latter situation, lactation may last longer that 5 months.
If a female is impregnated shortly after parturition, pregnancy and lactation may proceed simultaneously.
Calves are born in the warm tropical waters and subtropical waters of each hemisphere. Newborns are usually 4 to 5 m long, and are suckled by their mothers for about 5 months. The females' milk is highly nutritive, containing high amounts of fat, protein, lactose and water. There is no parental investment on the part of the males.
Humpback whales live in groups. They migrate seasonally from the tropics to the northern feeding grounds. In the tropics, they are found in dense aggregations on shallow banks. They are usually deep oceanic migrators between their feeding and breeding grounds; the vast majority of humpbacks do not come into coastal waters until they reach the latitudes of Long Island, New York or Cape Cod, Massachussetts. They tend to disperse more widely in deep waters than when in shallow water.
Humpbacks migrate between northern and southern latitudes in phase with the climactic cycle. Migration is largely connected with the two functions of feeding and reproduction. Megaptera novaeangliae regularly leaves colder waters (where the whales feed during the spring, summer, and fall) to goes to a winter range of shallow tropical banks (where feeding does not occur). These whales also tend to move through coastal waters during migrations when a land mass is in their direct route.
Humpbacks appear in large numbers in subarctic waters during the spring and remain there until the summer. As the season advances, they become less numerous. Humpbacks migrate apparently because they seek warmer water in which to bring forth their young. Pairing and mating also take place at about the same time in the warmer waters.
There is no direct evidence of territoriality. However, there are some types of preferred area sentiments by individuals or groups. This is supported by the seasonal returns to the same feeding and breeding grounds of most humpbacks.
Swimming speed may reach 27 km per hour and during migration, it may reach 3.8 to 14.3 km per hour. Whales with calves swim the slowest, whereas lone whales travel faster than those in groups.
Humpbacks dive 6 to 7 m for 15 to 20 minutes. During diving, blows are not regular and flukes are not lifted as the whale submerges. In longer dives, the flukes are lifted and the animal surfaces between dives for about 4 minutes, while blowing regularly.
Behaviors seen during courtship and feeding are as follows:
Megaptera novaeangliae also shows aggressive behaviors. "Escort" whales within a group may accompany whale-calf pairs. They become aggressive towards other humpbacks approaching the groups. They sometimes blow bubbles from their blow holes or mouths as an apparent "screen." It is believed that most "escorts" are males.
Protective or agonistic behavior may involve body thrashing, horizontal tail lashing, and lobtailing. This aggression may also be directed at boats for coming near the groups. In general, groups of whales are more aggressive than individual whales.
These whales also have realtionships with other animals. Humpbacks may compete with other rorquals (especially fin whales) for food. Also, many seabirds prey upon the same food as the humpbacks. Finally, minke whales, have been seen in close proximity to humpback populations.
Like minke whales, and fin whales, humpbacks are generalized feeders. They are highly mobile and opportunistic. Humpbacks feed upon plankton, the plant and animal life at the surface of the ocean's water, or upon fish in large patches or schools. Because of this, humpbacks are classified as "swallowers" and not "skimmers." They do eat commercially exploited fishes. Feeding by humpbacks takes place during the summer.
Atka makerel and Pacific saury are the most commonly found fish prey of humpbacks in the eastern North Pacific Ocean. The former is considered one of the favorite foods of humpback whales in waters off the Western Aleutians and South of the Amchitka Islands. In addition, humpbacks in the North Pacific and the Bering Sea eat euphausiids (krill), mackerel, sand lance, Ammodytes americanus, capelin and herring.
Fishes comprise about 95% of the diet of North Atlantic humpbacks. Those humpbacks living in the Atlantic Ocean, specifically near Cape Cod and Greenland, also eat sand lance, herring and pollock.
Humpbacks near Australia and in the Antartic also feed on euphausiids.
Typically, these whales take both food and water into their mouths. Large volumes can be accomodated because the ventral grooves in the throat allow for expansion. Once the mouth is full, it is closed and the water is pressed out. Meanwhile, the food is caught in the baleen plates and is then swallowed. This process is aided by the internal mechanism of rorqual feeding--the tongue.
Humpbacks have five main feeding behaviors (the first three are more commonly observed than the last two):
Bubble clouds are large inter-connected masses of bubbles formed by one underwater exhalation. Clouds concentrate or herd a mass of prey. Feeding is presumed to occur underwater. After that the humpback rises slowly to the surface within the bubble cloud. After several blows and some shallow diving, the manuever is repeated. Bubble clouds appear to assist in prey detection or capture by immobilizing or confusing prey. Bubble clouds may cause a jumping response among the prey, helping the whale to detect the prey, or it may disguise the whale from the prey.
Bubble columns are formed as a humpback swims underwater in a broad circle while exhaling. An individual column may form rows, semicircles, or complete circles. These circles act like a seive net, concentrating or herding the prey.
At times, humpbacks combine some of these methods, for example, combining bubble feeding and tail slapping (lobtailing), as they feed on sand lance.
It is important to note that no humpback younger than two years old uses the tail slapping method, although they are weaned from their mothers at one year. However, rudimentary lobtail feeding has been witnessed several times among older post-weaning young.
In addition, no difference has been noted in the frequency of lobtail feeding between the sexes.
Humpbacks have historically had incredible economic importance to humans. They were one of the nine species hunted intensively by whalers. They were at times the most important constituent of the catch of modern whalers. Their oil was in demand as a kind of burning oil for lamps and as a lubricant for machinery. Whale oil was also used as a raw material for margarine and as a component of cooking fat. Whale meat was processed for human consumption and made into animal feed. Meal made from whale bones was used as fertilizer.
However, these animals are no longer hunted extensively. They do continue to have some economic impact, as ecotourism and whale sighting tours are quite popular in appropriate coastal areas.
Humpback whales staying close to the shore on the Eastern Canadian seaboard damage cod and herring traps and can tear loose long lengths of a set net.
Currently, there are an estimated 6,000 humpbacks in the earth's waters, with possibly 1,000 to 3,000 more. The healthiest populations occur in the western north Atlantic Ocean. A few other areas in which there are small populations include the waters near Beguia, Cape Verde, Greenland, and Tonga. Global humpback populations have begun to strengthen, although this species is still a conservation concern.
Humpback whales received some protection in 1985 when the International Whaling Commission instituted a moratorium on commercial whaling. In the early part of the twentieth century, during the modern whaling era, humpback whales were highly vulnerable due to their tendency to aggregate on the tropical breeding grounds and to come close to the shore on the northern feeding grounds.
More than 60,000 humpbacks were killed between 1910 to 1916 in the southern hemisphere, and there were other peaks of exploitation in the 1930's and 1950's. In the North Pacific, there were peak catches of over 3,000 in 1962 to 1963.
In order to combat the problem of depletion, catching humpback whales was prohibited in the Antartic in 1939, although that plan was abandoned in 1949. In the southern hemisphere, hunting was banned in 1963. In the North Atlantic, hunting was banned in 1956. Finally hunting was banned in the North Pacific in 1966.
The common name "humpback" also comes from the animal's tendency to round its back when diving.
Some humpbacks have whitish, oval-shaped scars, which are the marks of parasitic sea lampreys. Humpback whales have few predators other than humans. They are sometimes harassed, perhaps killed, by killer whales, and sharks feed on their dead bodies.
Little is known about the diseases that affect humpback whales. However, true rorquals get cirrhosis of the liver and mastitis. It is unlear as to whether humpbacks also get them.
Humpbacks are the most parasitized of all of the Balaenopteridae. They tend to carry a wide variety of ecto and endoparasites. The number of parasites may be related to the swimming speed of this species. The slow pace of humpbacks is thought to allow accumulation of parasites to occur.
Humpbacks have different types of whale lice living in their scars, scratches, chins, throats, and urogenital slits. Barnacles also live in their throats, chins, and urogenital slits.
Some endoparasites that live within the whales are trematodes, cestodes, nematodes, acanthocephalans. Helminths live in the blubber, liver, mesentery, and intestine, while Ogmogaster ceti (a commensal nematode specific to the Balaenopteridae) lives in the baleen plates.
Pollutants that have been reported from the blubber of humpbacks include DDT, PCBs, chlordane, and dieldrin. The levels of these toxins vary during the migratory pattern of the humpbacks. The levels are highest during feeding and are lowest during breeding.
Nancy Shefferly (editor), Animal Diversity Web.
Mindy B. Kurlansky (author), University of Michigan-Ann Arbor.
the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats fish
an animal that mainly eats plankton
the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.
having more than one female as a mate at one time
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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