Megapterinae

The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus ''Megaptera''. Adults range in length from and weigh up to . The humpback has a distinctive body shape, with long pectoral fins and tubercles on its head. It is known for breaching and other distinctive surface behaviors, making it popular with whale watchers. Males produce a complex song typically lasting 4 to 33 minutes.

Found in oceans and seas around the world, humpback whales typically migrate up to each year. They feed in polar waters and migrate to tropical or subtropical waters to breed and give birth. Their diet consists mostly of krill and small fish, and they use bubbles to catch prey. They are promiscuous breeders, with both sexes having multiple partners. Orcas are the main natural predators of humpback whales.

Like other large whales, the humpback was a target for the whaling industry. Humans once hunted the species to the brink of extinction; its population fell to around 5,000 by the 1960s. Numbers have partially recovered to some 135,000 animals worldwide, while entanglement in fishing gear, collisions with ships, and noise pollution continue to affect the species.

Taxonomy

The humpback was first identified as ''baleine de la Nouvelle Angleterre'' by Mathurin Jacques Brisson in his ''Regnum Animale'' of 1756. In 1781, Georg Heinrich Borowski described the species, converting Brisson's name to its Latin equivalent, ''Balaena novaeangliae''. In 1804, Bernard Germain de Lacépède shifted the humpback from the family Balaenidae, renaming it ''B. jubartes''. In 1846, John Edward Gray created the genus ''Megaptera'', classifying the humpback as ''Megaptera longipinna'', but in 1932, Remington Kellogg reverted the species names to use Borowski's ''novaeangliae''. The common name is derived from the curving of their backs when diving. The generic name ''Megaptera'' from the Ancient Greek ''mega-'' ("giant") and ''ptera''/ ("wing") refer to their large front flippers. The specific name means "New Englander" and was probably given by Brisson due to regular sightings of humpbacks off the coast of New England.

Humpback whales are rorquals, members of the Balaenopteridae family, which includes the blue, fin, Bryde's, sei and minke whales. A 2018 genomic analysis estimates that rorquals diverged from other baleen whales in the late Miocene, between 10.5 and 7.5 million years ago. The humpback and fin whale were found to be sister taxon. There is reference to a humpback-blue whale hybrid in the South Pacific, attributed to marine biologist Michael Poole.

Modern humpback whale populations originated in the southern hemisphere around 880,000 years ago and colonized the northern hemisphere 200,000–50,000 years ago. A 2014 genetic study suggested that the separate populations in the North Atlantic, North Pacific, and Southern Oceans have had limited gene flow and are distinct enough to be subspecies, with the scientific names of ''M. n. novaeangliae'', ''M. n. kuzira'' and ''M. n. australis'' respectively. A non-migratory population in the Arabian sea has been isolated for 70,000 years.

Description

The adult humpback whale is generally , though longer lengths of have been recorded. Females are usually longer than males. The species can reach body masses of . Calves are born at around long with a weight of .

The body is bulky with a thin rostrum and proportionally long flippers, each around one-third of its body length. It has a short dorsal fin that varies from nearly non-existent to somewhat long and curved. As a rorqual, the humpback has grooves between the tip of the lower jaw and the navel. They are relatively few in number in this species, ranging from 14–35. The mouth is lined with baleen plates, which number 270-400 for both sides.

Unique among large whales, humpbacks have bumps or tubercles on the head and front edge of the flippers; the tail fluke has a jagged trailing edge. The tubercles on the head are thick at the base and poke up to . They are mostly hollow in the center, often containing at least one fragile hair that erupts from the skin and is thick. The tubercles develop early in the womb and may have a sensory function as they are rich in nerves.

The dorsal or upper-side of the animal is generally black; the ventral or underside has various levels of black and white coloration. Whales in the southern hemisphere tend to have more white pigmentation. The flippers can vary from all-white to white only on the undersurface. The varying color patterns and scars on the tail flukes distinguish individual animals. The end of the genital slit of the female is marked by a round lobe. This lobe visually distinguishes males and females.

Behavior and ecology

Humpback whale groups, aside from mothers and calves, typically last for days or weeks at the most. They are normally sighted in small groups though large aggregations form during feeding and among males competing for females. Humpbacks may interact with other cetacean species, such as right whales, fin whales, and bottlenose dolphins. Humpbacks are highly active at the surface, performing aerial behaviors such as breaching and surface slapping with the tail ( lobtailing) and flippers. These may be forms of play and communication and/or for removing parasites.

Humpbacks rest at the surface with their bodies laying horizontally. The species is a slower swimmer than other rorquals, cruising at . When threatened, a humpback may speed up to . They appear to dive within and rarely below . Dives typically do not exceed five minutes during the summer but are normally 15–20 minutes during the winter. As it dives, a humpback typically raises its tail fluke, exposing the underside.

Feeding

Humpback whales feed from spring to fall. They are generalist feeders, their main food items being krill and small schooling fish. The most common krill species eaten in the southern hemisphere is the Antarctic krill. Further north, the northern krill and various species of '' Euphausia'' and '' Thysanoessa'' are consumed. Fish prey include herring, capelin, sand lances and Atlantic mackerel. Like other rorquals, humpbacks are "gulp feeders", shallowing prey in bulk, while right whales and bowhead whales are skimmers. The whale increases its mouth gape by expanding the grooves. Water is pushed out through the baleen. In the southern hemisphere, humpbacks have been recorded foraging in large compact gatherings numbering up to 200 individuals.

Humpbacks hunt their prey by performing bubble-net feeding. A group of whales swim in a shrinking circle while blowing air from their blowholes, capturing the prey above them in a cylinder of bubbles. They may dive up to performing this technique. Bubble-netting comes in two main forms; upward spirals and double loops. Upward spirals involve the whales blowing air from their blowhole continuously as they circle towards the surface, creating a spiral of bubbles. Double loops consist of a deep, long loop of bubbles that herds the prey, followed by slapping the surface and then a smaller loop that prepares the final capture. Combinations of spiraling and looping have been recorded. After the humpbacks create the "nets", the whales swim into them with their mouths gaping and ready to swallow.

Using network-based diffusion analysis, one study argued that whales learned lobtailing from other whales in the group over 27 years in response to a change in primary prey. The tubercles on the flippers stall the angle of attack, which both maximizes lift and minimizes drag (see tubercle effect). This, along with the shape of the flippers, allows the whales to make the abrupt turns necessary during bubble-feeding.

Courtship and reproduction

Mating and breeding take place during the winter months, which is when females reach estrus and males reach peak testosterone and sperm levels. Humpback whales are promiscuous, with both sexes having multiple partners. Males will frequently trail both lone females and cow–calf pairs. These are known as "escorts", and the male that is closest to the female is known as the "principal escort", who fights off the other suitors known as "challengers". Other males, called "secondary escorts", trail further behind and are not directly involved in the conflict. Agonistic behavior between males consists of tail slashing, ramming, and head-butting.

Gestation in the species lasts 11.5 months, and females reproduce every two years. Humpback whale births have been rarely observed. One birth witnessed off Madagascar occurred within four minutes. Mothers typically give birth in mid-winter, usually to a single calf. Calves suckle for up to a year but can eat adult food in six months. Humpbacks are sexually mature at 5–10 years, depending on the population. The length at maturity is around . Humpack whales possibly live over 50 years.

Vocalizations

Male humpback whales produce complex songs during the winter breeding season. These vocals range in frequency between 100 Hz to 4 Hz, with harmonics reaching up to 24 kHz or more, and can travel at least . Males may sing for between 4 and 33 minutes, depending on the region. In Hawaii, humpback whales have been recorded vocalizing for as long as 7 hours. Songs are divided into layers; "subunits", "units", "subphrases", "phrases" and "themes". A subunit refers to the discontinuities or inflections of a sound while full units are individual sounds, similar to musical notes. A succession of units creates a subphrase, and a collection of subphrases make up a phrase. Similar-sounding phrases are repeated in a series grouped into themes, and multiple themes create a song.

The function of these songs has been debated, but they may have multiple purposes. There is little evidence to suggest that songs establish dominance among males. However, there have been observations of non-singing males disrupting singers, possibly in aggression. Those who join singers are males who were not previously singing. Females do not appear to approach singers that are alone, but may be drawn to gatherings of singing males, much like a lek mating system. Another possibility is that songs bring in foreign whales to populate the breeding grounds. It has also been suggested that humpback whale songs have echolocating properties and may serve to locate other whales.

Whale songs are similar among males in a specific area. Males may alter their songs over time, and others in contact with them copy these changes. They have been shown in some cases to spread "horizontally" between neighboring populations throughout successive breeding seasons. In the northern hemisphere, songs change more gradually while southern hemisphere songs go through cyclical "revolutions".

Humpback whales are reported to make other vocalizations. "Snorts" are quick low-frequency sounds commonly heard among animals in groups consisting of a mother–calf pair and one or more male escort groups. These likely function in mediate interactions within these groups. "Grumbles" are also low in frequency but last longer and are more often made by groups with one or more adult males. They appear to signal body size and may serve to establish social status. "Thwops" and "wops" are frequency modulated vocals, and may serve as contact calls both within and between groups. High-pitched "cries" and "violins" and modulated "shrieks" are normally heard in groups with two or more males and are associated with competition. Humpback whales produce short, low-frequency "grunts" and short, modulated "barks" when joining new groups.

Predation

Visible scars indicate that orcas prey upon juvenile humpbacks. A 2014 study in Western Australia observed that when available in large numbers, young humpbacks can be attacked and sometimes killed by orcas. Moreover, mothers and (possibly related) adults escort calves to deter such predation. The suggestion is that when humpbacks suffered near-extinction during the whaling era, orcas turned to other prey but are now resuming their former practice. There is also evidence that humpback whales will defend against or mob killer whales who are attacking either humpback calves or juveniles as well as members of other species, including seals. The humpback's protection of other species may be unintentional, a "spillover" of mobbing behavior intended to protect members of its species. The powerful flippers of humpback whales, often infested with large, sharp barnacles, are formidable weapons against orcas. When threatened, they will thresh their flippers and tails keeping the orcas at bay.

The great white shark is another confirmed predator of the humpback whale. In 2020, Marine biologists Dines and Gennari ''et al.'', published a documented incident of a group of great white sharks exhibiting pack-like behavior to attack and kill a live adult humpback whale. A second incident regarding great white sharks killing humpback whales was documented off the coast of South Africa. The shark recorded instigating the attack was a female nicknamed "Helen". Working alone, the shark attacked a emaciated and entangled humpback whale by attacking the whale's tail to cripple and bleed the whale before she managed to drown the whale by biting onto its head and pulling it underwater.

Range

Humpback whales are found worldwide, except for some areas at the equator and High Arctic and some enclosed seas. The furthest north they have been recorded is at 81°N around northern Franz Josef Land. They are usually coastal and tend to congregate in waters within continental shelves. Their winter breeding grounds are located around the equator; their summer feeding areas are found in colder waters, including near the polar ice caps. Humpbacks go on vast migrations between their feeding and breeding areas, often crossing the open ocean. The species has been recorded traveling up to in one direction. An isolated, non-migratory population feeds and breeds in the northern Indian Ocean, mainly in the Arabian Sea around Oman. This population has also been recorded in the Gulf of Aden, the Persian Gulf, and off the coasts of Pakistan and India.

In the North Atlantic, there are two separate wintering populations, one in the West Indies, from Cuba to northern Venezuela, and the other in the Cape Verde Islands and northwest Africa. During summer, West Indies humpbacks congregate off New England, eastern Canada, and western Greenland, while the Cape Verde population gathers around Iceland and Norway. There is some overlap in the summer ranges of these populations, and West Indies humpbacks have been documented feeding further east. Whale visits into the Gulf of Mexico have been infrequent but have occurred in the gulf historically. They were considered to be uncommon in the Mediterranean Sea, but increased sightings, including re-sightings, indicate that more whales may colonize or recolonize it in the future.

The North Pacific has at least four breeding populations: off Mexico (including Baja California and the Revillagigedos Islands), Central America, the Hawaiian Islands, and both Okinawa and the Philippines. The Mexican population forages from the Aleutian Islands to California, particularly the Bering Sea, northern and western Gulf of Alaska, southern British Columbia to northern Washington State, and Oregon to California. During the summer, Central American humpbacks are found only off Oregon and California. In contrast, Hawaiian humpbacks have a wide feeding range but most travel to southeast Alaska and northern British Columbia. The wintering grounds of the Okinawa/Philippines population are mainly around the Russian Far East. There is some evidence for a fifth population somewhere in the northwestern Pacific. These whales are recorded to feed off the Aleutians with a breeding area somewhere south of the Bonin Islands.

Southern Hemisphere

In the Southern Hemisphere, humpback whales are divided into seven breeding stocks, some of which are further divided into sub-structures. These include the southeastern Pacific (stock G), southwestern Atlantic (stock A), southeastern Atlantic (stock B), southwestern Indian Ocean (stock C), southeastern Indian Ocean (stock D), southwestern Pacific (stock E), and the Oceania stock (stocks E–F). Stock G breeds in tropical and subtropical waters off the west coast of Central and South America and forages along the west coast of the Antarctic Peninsula, the South Orkney Islands

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