Humpback Whale

Latin: Megaptera novaeangliae
Gaelic: Muc-mhara-crotach

Physical Description

The humpback whale is very easily distinguished from other baleen whales by its distinctive appearance. The head has a number of knobbly tubercles, which are in-fact enlarged hair follicles. Fourteen to twenty-two white ventral pleats extend from the lower jaw to mid-way down the belly. The dorsal fin is small and hooked, located far down the back on the hump, and is often scarred. Pectoral (side) fins are long and narrow (Megaptera means “great wing”) and may measure as much as a third of the body length. When fully grown, humpback whales can measure up to 17 metres and weigh 40,000 kg; the female is normally slightly larger than the male. The body is predominantly black with white patches on the belly and mostly white pectoral fins. The tail fluke can measure up to five metres across, has a serrated trailing edge, and is black with distinct patterns of white on the underside; this pattern is unique to each animal and is used for identifying individuals. Their blow is described as ‘bushy’ and can be as tall as four metres.

Habitat and Distribution

Humpback whales are widely distributed throughout all oceans of the world, and are highly migratory. They travel thousands of miles from warm-water breeding grounds in the tropics to the cold-water feeding grounds in the polar regions. They favour inshore waters and continental shelf areas, but will travel through open water during their migration. Humpback whales are occasionally encountered in the Hebrides travelling between breeding grounds off Africa to feeding grounds around Iceland and Norway; there are one or two sightings in the Hebrides each year. Sea-bed mounted hydrophones (underwater microphones) have also recorded humpback whale presence in UK waters.

Behaviour

The behaviour of humpback whales varies according to the season. During breeding periods in the tropics, humpback whales do not feed and survive on fat (blubber) reserves. Male whales sing long, complex songs during the breeding season, presumably to attract females and warn off rival males. These songs are known to vary between populations and change over time. Competition between males can become aggressive and may involve lunges, charges and tail swipes. Year-round, humpback whales are normally seen as solitary individuals or in small groups of up to seven animals, and long-term associations are rare. In general, humpback whales are well-known for their energetic displays of breaching and lob-tailing, although the reason for these behaviours is not fully understood. They can dive for up to 40 minutes and raise their tail fluke when making a deep dive. Humpback whales can also be very inquisitive and may approach boats where they will spy hop and flipper-slap. Sightings of humpback whales in the Hebrides are rare and the behaviours described here are based on encounters from elsewhere in the world.

Food and Foraging

Humpback whales are thought to feed mainly on krill, herring and cod when in British waters. Their prey is filtered from the water by stiff baleen plates inside the mouth, and swallowed whole. Whales may forage alone, or in groups. Humpbacks have developed a sophisticated technique known as ‘bubble-netting’ where the whales produce a ring of bubbles to drive the fish together and push them up towards the surface where they can be caught in huge gulp. The fish appear disorientated and unwilling to swim through the bubbles.

Status and Conservation

Historically, humpback whales were targeted by commercial whalers and the global population was consequently severely depleted. Today, humpback whales face a range of threats including collisions with vessels, entanglement in fishing gear, pollution and reduction in prey stocks. In the UK, sightings are very rare although there is evidence that the North Atlantic population has recovered somewhat since the whaling moratorium was established in 1982. Humpback whales are now popular with whale-watching trips worldwide. Humpback whales are protected under UK and EU law, principally under Schedule 5 of the Wildlife and Countryside Act 1981, the Nature Conservation (Scotland) Act 2004 and by the 1992 EU Habitats and Species Directive.