Humpback Whales
Size: Females = 17-18 m (56-59 ft) and Males = 16 m (52 ft)
Weight: 40 tonnes
Diet: Primarily sandeels, capelin, herring and krill.
Humpback whales are large baleen whales belonging to the rorqual family. They are classified into a separate genus called Megaptera or “big-winged”. Humpback whales are the only member of this genus, although recent studies have shown that they are most closely related to the fin whale of all other rorquals. Their most defining characteristics are their enormously long pectoral fins as well as the fact they are stockier in shape than other rorquals and have a relatively large head and broad tail. Humpback whales have charmed whale-watchers throughout the world, as they are extremely curious about seafarers and frequently perform aerial displays such as breaching and slapping the water with their fins and tails.
Behavior
Humpback whales are without a doubt among the liveliest of the larger whales at the surface. They commonly roll over, leap out of the sea and slap their fins and flukes on the surface with a lot of splashing. They also often stick their head straight out of the ocean, probably to investigate conditions on the surface. This behaviour is called spy-hopping. They often seek out boats and follow them for a while. Humpback whales are usually on their own, although it is not uncommon to see them in smaller groups consisting of 2–5 animals. These groups do not remain together for long, so they rarely form close bonds, with the exception of females and their calves. Hundreds of humpbacks can, however, congregate in areas where there is an abundance of food. The groups are particularly unstable in the feeding grounds during the summer and only stay together for a few hours at a time. The groups usually consist of animals of the same gender and age. In the breeding grounds in the winter, the groups variously consist of a) only males, b) mother and calf or c) mother, calf and a few escorting males. The escorting males often follow the mother and calf for a long time waiting for an opportunity to mate. The largest and strongest male keeps the other escorting males away and is therefore the most likely to mate with the female.
Humpback whales are rather slow swimmers, travelling at around 8 kph (5 mph) during migration. They can, however, swim at up to 27 kph (17 mph) in shorter bursts. Deep dives are generally of short duration, or 10 minutes, as is common among other rorquals, although they can dive for up to 30 minutes to a depth of at least 250 m (820 ft.).
Reproduction
Reproduction in the North Atlantic takes place during the period between December and April and peaks in February and March. Gestation lasts 11–12 months, with the females usually giving birth to a single calf. Although there are examples of twin fetuses, no female has ever been seen with two calves suckling at the same time. The females generally calve every other year, and the older the mother, the more likely the calf is to survive. The calves suckle for only 6 months, although lactation can remain active for up to a year.
Vocalization
Humpback whales are famous for their complicated and varied vocalization. The males sing complicated and long songs during migration and during the mating season. These songs have been likened to birdsong, except humpback whale songs can last for up to an hour while birdsong lasts for only a few seconds. The object of the song has not been fully defined but is obviously linked to courtship. Every year, the males sing the same or a similar song at each mating station. The song, however, develops over time and differs between years. The songs are probably used to attract the females toward the males and may also help the males to keep a certain distance from each other. Females and males also emit a number of communication sounds that indicate either friendliness or dislike. When meeting and separating, they often emit various low-frequency sounds such as grunts, growls and woops. When indicating dislike, they emit a high-frequency scream. Calls at lower frequencies are probably used to let others know of their location.
Habitat and distribution
Humpback whales can be found in any ocean, right from equatorial areas to the edge of the icepack in the Polar Regions. Humpback whales are migratory and spend summers in feeding grounds in higher latitudes toward the Polar Regions where food is abundant. During the autumn and early winter, they migrate in the direction of the Equator to their mating grounds and may travel up to 17,000 km (10,563 miles) every year. The calves learn the migration route by following their mothers to the feeding ground during their first spring and remain faithful to that area thereafter. Not all humpback whales appear to migrate every year. In such cases when they do not, they remain at the feeding grounds throughout the winter where the food is available all year round. It is quite common for humpback whales to remain off the shores of Iceland throughout the winter, and recent studies indicate that a proportion may mate here in Iceland.
Life expectancy and population size
Humpback whales can live to at least 50 years of age, although their maximum life expectancy is not fully known. Humpback whales have been classified into 12 distinct breeding stocks throughout the world, whereof two are in the North Atlantic Ocean. One of these breeds in the Caribbean and Gulf of Mexico, while the other breeds near the Cape Verde Islands off the shores of north-west Africa. Humpback whales of both these stocks are believed to mingle off the coast of Iceland. The population in the North Atlantic Ocean is believed to be around 15,000 animals, whereof at least 5,000 are thought to be in the waters off Iceland during the summer.
Humpback whales have recovered remarkably well in the North Atlantic after intensive whaling at the close of the 19th century, being extremely rare in Icelandic waters for most of the 20th century. At present, humpback whales sometimes get entangled and drown in fishing nets and collide with ships. The humpback whale’s main natural enemy is the killer whale, which tends to target the calves.
Edda Elísabet Magnúsdóttir, Marine Biologist