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Humpback whales by Courtney    

Humpback Whales: A Short Article by Courtney

A marine conservation essay from Project Ocean Vision


The Humpback Whale Megaptera novaeangliae

Humpback Whale - Project Ocean Vision, marine conservation

CLASS:

ORDER:

SUBORDER:

FAMILY:

GENUS:

SPECIES:

Mammalia

Cetacea

Mysticeti

Balaenopteridae

Megaptera

Novaeangliae


CETACEA

Cetacea, the whales, evolved from terrestrial, hoofed mammals some 45 million years ago, adapting to the aquatic environment. This is an example of adaptive radiation (a rapid increase in the disparity of a single, rapidly diversifying, biological lineage), which has allowed mammals to evolve, to exploit openings in the ecospace and to inhabit the land, sea, and air.

In so doing, cetaceans have a number of adaptations that suit them to the marine environment:

Streamlined for efficient movement through water,

Forelimbs have developed into pectoral fins that aid stability and control when swimming,

Redundant hind limbs have disappeared almost completely,

A horizontally broadened tail that consists of two large flukes to give efficient propulsion through water using powerful vertical strokes,

A thick layer of blubber under their skin that provides thermal insulation and buoyancy,

Nostrils located on the top of the head creating the blowhole that allows the rapid exchange of air at the surface.

Whales are highly intelligent mammals and the order cetacea is divided into two sub-orders: odontocetes and mysticeti. Let's briefly look at each of these before moving on to Humpbacks and the conservation issues in more detail.

The odontocetes are the toothed whales , which include sperm whales, killer whales (orcas), dolphins and porpoises. They develop a single set of teeth, none of which is ever replaced and they are all carnivores hunting fish, squid, and animals such as seals, crabs, turtles and seabirds, depending on species. The Orcas will take other marine mamals, including seals, sea lions and larger whales. Odontocetes' daily consumption of food ranges between 5 and 20% of their body weight, they feed all year round and do not typically migrate. Toothed whales have a single blowhole producing a single spout directed diagonally forward.

The second sub-order, mysticeti, the baleen whales, includes the Humpback, gray and blue whales. Their main distinguishing characteristic is that all adults lack teeth and instead have two rows of baleen plates hanging from either side of their upper jaw. Baleen, incorrectly know as ‘whalebone' is made of keratin , the protein that constructs hair, nails, and animal hooves and horns. Certain species possess over 400 baleen plates, each less than 5mm thick and fringed with hairs along the inner edge. The plates are black and measure up to a metre long in Blue whales (80 cm in Humpbacks). They act as sieves, separating their minute prey from the water – Humpback feeding is described shortly. Baleen whales have a double blowhole creating a distinctive v-shaped spout.


Baleen
Whale skull in the Natural History Museum, London, showing the baleen plates

 

HUMPBACK WHALES

The Humpback whale is arguably the best-studied and most interesting of the baleen whales. They are highly vocal, singing complex songs that can be herd over 20 miles away. We are not sure exactly how Humpback whales produce sound as they do not have vocal cords. It is thought that they sing by circulating air through the tubes and chambers of their respiratory system without releasing any air. Only male humpback whales sing and do so whilst hanging vertically, head-down, in the water.

Interestingly, at any one time, all the humpback whales in each population sing their own song, but each population's song is different. A typical humpback whale song lasts up to 20 minutes, is repeated continuously for hours at a time and changes gradually from year to year.



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Click on the play button to play humpback whale song



Humpback whales can be easily identified by their stocky body with obvious humps and black dorsal (upper) parts. Their throats and the ventral (lower) sides of the flukes and pectoral fins have distinct white markings. The shape and pattern of these markings are as distinctive as human fingerprints and are used by researchers to identify individuals and to gain valuable information about population sizes, sexual maturity, migration and behaviour patterns.

Humpback whale flukes
Humpback whale flukes


Humpback whale sounding
Humpback whale sounding

The name Humpback describes the motion it makes as it arches its back out of the water in preparation for a dive or ‘sound'. The tail is often lifted clear of the water as the whale sounds, revealing the wavy trailing edges of the flukes, which can measure over 5 metres across. On surfacing, their characteristic double spout can reach 3 to 6 metres high. Humpback whales are easily recognized by their enormous pectoral fins, which can reach a third of their body length, maybe 5 metres in some cases. The pectoral fins range from all white to all black dorsally, but are usually white ventrally. Adult Humpback whales range in size from 12 to 16 metres long and weigh up to 36 tonnes.


Viewed from above, a humpback whale's head is roundly broad, but relatively slim in profile. The body is quite round, narrowing to a slender peduncle. The top of the head and lower jaw have rounded bumps called tubercles, each containing at least one stiff hair. These are actually hair follicles and their purpose is not known, but it is thought that they allow the whale to sense movement in the water and are a legacy of their mammalian heritage.

Humpback whale drawing
Humpback Whale


Humpback whales are also described as rorquals, a family that includes the blue whale, fin whale, sei whale and minke whale. Rorquals have two characteristics in common: a dorsal fin and ventral pleats that run from the tip of the lower jaw to slightly beyond the navel. In the case of Humpback whales, there are between 14 and 35 of these - somewhat less obvious than the other rorquals. The pleats allow the throat to expand, enabling the whale to take in huge quantities of water, which is then expelled and sieved through the baleen plates. The whale can then swallow the trapped plankton. Humpback whales (like all baleen whales) are seasonal feeders and carnivores that feed on amphipods, plankton, and small fish including herring, capelin, mackerel, and sandeel. An average-sized Humpback whale will eat 2,000-2,500 kg each day in cold waters during the feeding season of about 3 months. They generally eat twice a day.

One of the Humpback whale's most impressive feeding techniques is called bubble netting. A heard of roughly a dozen Humpback whales circle around and under a school of fish, blowing air through their blowholes to form a visual barrier up to 30 metres across that confines the fish. One Humpback whale will then swim rapidly upwards through the bubble net to catch thousands of them in a single pass.

Humpback whales are found in all the world's oceans, most numerous in the southern hemisphere, and most populations follow regular migration routes from tropical and subtropical breeding sites in winter to the polar feeding grounds in summer. There is known to be a non-migratory population in the Arabian Sea.


Humpback whale flipper slapping
Humpback whale flipper slapping

Humpback whales mature sexually between about 6 and 15 years of age or when males reach the length of 11.6 metres, 12 metres for females. The male's penis usually remains hidden in the genital slit, but males and females can be distinguished from the underside by the females' hemispherical lobe about 15 centimetres in diameter in their genital region. Courtship takes place during the winter months and competition for a mate is fierce. Groups of 20 or more males gather around a single female to display in order to establish dominance. The displays last several hours during which time unsuccessful males retreat and others may arrive. Rituals include breaching, spy-hopping, lob-tailing, tail-slapping, flipper-slapping, charging and parrying – see the glossary at the bottom of this article.


Each female Humpback whale typically bears a calf every 2 to 3 years, although some individuals can breed in consecutive years and the gestation period is 11.5 months. A Humpback whale calf is between 4 and 4.5 metres long at birth, and weighs around 800 kg. It nurses frequently on the mother's rich milk, which has a fat content of 45 to 60%, and drinks about 45 kg each day. Weaning starts when the calf is about six months old and is complete by the end of its first year. Calves leave their mothers at the start of their second year when they are typically 9 metres long. A Humpback Whale can live for 50 years.

At least 3 different species of barnacles are commonly found on both the flippers and the body of the Humpback whale. It is also host to a species of whale lice, Cyamus boopis.


Humpback whales tend to feed, mate and calve relatively close to shore and they are slow swimmers. They are highly social and often hunt and travel in pods of 200 or more, although they tend to be more dispersed during migration. These characteristics made Humpback whales easy targets for early whalers and of great interest to conservationists today. In the early and mid 20th century, Humpback whale populations were decimated as they were hunted for their oil and baleen. In the mid-1960s the International Whaling Commission (IWC) imposed a ban, protecting them from further exploitation, although there was a lot of illegal hunting, mainly by the Soviets, until the 1970s. It is believed they number about 30,000-40,000 at present, only about 30-35% of the original population.


Humpback whale breaching
Humpback whale breaching

There are a number of very worthy conservation organizations actively trying to protect Humpback whales (and other cetacieans). Among them, The Whale and Dolphin Conservation Society, Earthwatch, The World Wildlife Fund and, of course, Greenpeace.

 


GLOSSARY

Amphipods

Crustaceans of the order Amphipoda, important food for baleen whales.

Amphipod

Baleen

Fibrous plates, made from keratin, that hang from the upper jaw of baleen whales (Mystecetes), used filter food from seawater. Also called ‘whalebone'.

Blow

Also known as spout, it is a visible cloud of moisture laden exhalation by cetaceans.

Blowhole

In cetaceans, the single or paired respiratory opening on top of the head.

Breaching

A behaviour of cetaceans that jumps or leaps out of the water and re-enters on its side or back making a huge splash for a variety of purposes including courtship.

Bubble net feeding

A cooperative feeding technique of Humpback whales, exhaling bubbles underwater to form a cylindrical net to entrap schooling fish.

Bull

Adult male whale.

Calf

Baby whale – generally under 2 years of age.

Caudal

Of, pertaining to, or near the tail or posterior part of the body.

Cetacean

An aquatic (usually marine) mammal of the order Cetacea: whales, porpoises and dolphins.

Copepods

Small, shrimp-like crustaceans, important food for baleen whales.

Copepod

Cow

Adult female whale.

Cyamids

Also called whale lice, they are members of the family Cyamidae, related to crabs and shrimp. These parasitic crustaceans live on whales and feed on their skin. Cyamids infest only whales.

Dolphin

Smaller, beaked, toothed whales with conical teeth. Note that there is also a dolphin fish, better known as Dorado or Mahi-Mahi.

Dorsal

Pertaining to or of the back or upper surface of the body.

Dorsal fin

The fin along the midline of the back (the top fin in marine vertebrates).

Flippers

Pectoral fins. In cetaceans, the forelimbs. More generally the limbs of marine mammals, including pinnipeds.

Flipper slapping

The behaviour of slamming their flippers at the water surface. Also called ‘flippering' or ‘pec-slap'.

Fluke

Either of the two horizontal lobes of a whale's tail.

Herd

A group of baleen whales.

IWC

International Whaling Commission. An international body formed in 1946 to regulate whaling and conserve whale stocks.

Krill

Small shrimp-like crustaceans belonging to the family Euphasiidae; an important food source for baleen whales.

krill

Lobtailing

The behaviour of slapping the flukes at the surface of the water. Also called ‘tail-slapping'.

Mammal

A member of the class Mammalia, warm blooded animals that have lungs, hair, give birth to live young, which they suckle.

Marine mammals

Mammals that live in the sea. These include whales, dolphins, and porpoises (cetacea), seals, sea lions, and walruses (pinnipeds), dugongs and manatees (sirinians), otters, and polar bears.

Odontoceti

The scientific term for the suborder of toothed whales.

Pectoral fin

In cetaceans, the forelimbs. More generally the limbs of marine mammals, including pinnipeds.

Plankton

Microscopic plants (phytoplankton) and animals (zooplankton) swimming weakly or drifting on ocean currents. This is an important source of food for baleen whales.

Porpoise

Commonly used interchangeably with ‘dolphin', but defined as a cetacean with a short beak or no beak, spade-shaped teeth, and a triangular dorsal fin. See also Dolphin for comparison.

Rorqual

A term used for baleen whales belonging to the genus Balaenoptera, which includes the blue, fin, sei, Bryde's, and the Minke whales. Some include the Humpback whale of the genus Magaptera. The characteristics of rorquals are numerous longitudinal grooves (long throat grooves) on the lower surface of the body, and a dorsal fin.

Sounding

The display of the flukes as a Humpback submerges for a deep dive.

Spout

Also known as a ‘blow', it is a visible cloud of moisture laden exhalation by cetaceans

Spy hopping

The behaviour in cetaceans that involves raising the head vertically out of the water, then sinking back into the water without causing much splash.

Tubercles

Small bumps found on the flippers and dorsal fins of some cetaceans (e.g., harbour and Burmeister porpoise). Also the knobs found on the head and jaws of some Humpback whales. Each tubercle is also called a ‘stovebolt' and contains a single hair called ‘vibrissa'.

Ventral

Pertaining to the underside or lower part of the body.

Ventral grooves

Pleats or furrows that extend down to the throat or the navel, in baleen whales belonging to the family Balaenopteridae. Like an accordion this helps to expand the throat. Smaller throat grooves can be found in gray and beaked whales.

Whale lice

Cyamids are crustaceans live on whales and feed on their skin. They usually accumulate on areas with reduced water flow.

Whalebone

See baleen.



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