Humpback Whale

Description - Range & Habitat - Behavior - Reproduction - Food & Foraging - Status & Conservation

Megaptera novaeangliae - (Kohola)

Maximum Length: 52-56’ (13 m)
Maximum Weight: 90,000 lb (36,000 kg)
Life Span: More than 50 years

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Cetacea (whales and dolphins)
Sub-Order: Mysticeti (baleen whales)
Family: Balaenopteridae (rorquals)
Genus: Megaptera (big wings)
Species: novaeangliae (of New England)

Description

Humpback whales are the most familiar of the great whales. Their spectacular acrobatic displays can easily be observed from coastal shorelines and by passing boaters. Although other baleen whales are occasionally seen in Hawaii, humpback whales are considered to be the only seasonal residents. However, the occasional but rare observation of a Northern right whale [1], and a fin whale [2] in Hawai’ian waters has been noted.

Humpback whales have some very unique characteristics that separate them from the rest of the rorquals. They possess tubercles on the top of their head and lower jaw, each of which contains one or two hairs believed to be sensory related. Another unique characteristic is their long pectoral fins, reaching up to one third of their body length. Humpbacks are described by their scientific name, Megaptera novaeangliae, which translates to “big-winged New Englander,” referring to a historic prime feeding area off the New England coast.

Humpback whales have bodies that are black in color on their dorsal surface and black, white, or mottled ventrally. North Pacific humpbacks tend to have less white compared with the Atlantic and Southern hemisphere humpbacks. As is the case for all baleen whales, females are on average about one meter longer than adult males [3, 4].

Humpbacks possess 13 to 22 ventral pleats extending down their throat to the umbilicus. These are fewer and more spread apart than in other rorquals. The dorsal fin is variable in shape and is characterized by a unique bump or hump, just ahead of the dorsal fin. This hump is how they received their common name, “humpback.”

The white and dark pigmentation patterns, on the ventral side of their tail flukes, are unique to each individual. Additionally, the trailing edge of each fluke has a uniquely serrated edge. As the whale lifts its tail out of the water on its final dive, researchers will photograph this unique “fingerprint” (see photo-identification). The matching of new photographs against previous photographs helps develop life histories of individual whales.

Humpbacks also have a blow that is lower, rounder, and bushier compared with other rorquals.

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Range and Habitat

Humpback whales feed during the summer months in mid to high latitudes [3, 5, 6]. They visit their breeding and calving grounds, in shallow tropical and subtropical waters, during the winter months [7, 8]. This seasonal migration for some humpbacks can consist of a distance of 4800 miles one-way (8000 km) [9], the longest migration known of any mammal. Mating and calving grounds are usually concentrated around islands or reef systems.

Although all the whales will undertake this migration at some point in time, it appears that some females may overwinter in high latitudes ([10-13]

Humpbacks are found in all major oceans worldwide. The three major populations of humpbacks include the North Pacific, the North Atlantic, and the Antarctic populations. A fourth population known as the Arabian Sea population is considered unique, since these animals remain in tropical waters year-round. Hawaii

Humpback whales in Hawaii occur almost exclusively within the 100-fathom (183 meter) contours surrounding the main Hawai’ian islands (Herman and Antinoja, 1977; Wolman and Jurasz, 1977). The largest concentrations occur around the shallow Penguin Bank area, extending about 25 nm off the west coast of Molokai, and within the four-island region between Maui, Molokai, Lanai, and Kahoolawe (Herman and Antinoja, 1977; Wolman and Jurasz, 1977).

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Breach	Head Slap	Pec Slap	Peduncle Slap	Tail Slap

Humpback whales are generally found in small, unstable groups both on the feeding grounds [14-17], and on the breeding grounds [18-20]. Larger groups may form around food sources [11, 21] or in association with males competing for access to a female on the breeding grounds [22-24]. The strongest association between any two individual humpbacks is between a mother and her calf, lasting less than one year. Juveniles will become less solitary with age [25].

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Reproduction

Arrival of individuals to the Hawai’ian reproductive grounds usually begins around early December. Not all humpbacks migrate at one time; they have a staggered arrival known as the “migratory parade” [3, 6, 26, 27]. The first groups of whales to arrive are the lactating mothers with their calves from the previous year, or “yearling.” Sexually immature whales (under 5 years of age) are the next group of whales to arrive, followed by mature males, mature mating females, and lastly the pregnant females or females who have recently given birth. The whales depart the reproductive grounds in the reverse order, with newly pregnant females leaving first and the mothers with the calves leaving last.

Residency while on the mating grounds can last anywhere between 2 to 8 weeks, during which time the whales are fasting. Females will likely return immediately to the feeding grounds, once they become pregnant. This may occur prior to them arriving at their destination and is partly responsible for the 2 to 1 male to female ratio observed on the reproductive grounds [23, 28].

Sexually mature females presumably migrate to the reproductive grounds to mate and give birth. Although actual mating between two humpbacks has never been documented, females come into estrus only during the winter; and, testosterone levels and sperm production in males peak during this time of year [3, 29, 30]. The duration of estrus for females is unknown, but is suspected to last several days [31]. Females are rarely resighted after being observed in a competitive group [23], supporting the idea that they begin the return migration to higher latitudes after becoming pregnant [3, 6].

Adult females, although capable of giving birth in consecutive years [32], typically give birth on average every 2 to 3years [33]. This is likely due to the tremendous energy expenditure required from the mother during lactation [34]. The gestation period is between 11 and 12 months. To facilitate birth, the dorsal fin and flukes of the calf are soft. During the first few days following birth the dorsal fin and flukes will solidify, and the dorsal fin will become upright. A newborn calf can be 12-15 feet long weighing up to 4,000 lbs. Calves will nearly double its size in their first year of life. They will nurse on their mother’s milk, containing nearly 35% fat, for about 6 months before they begin to feed on solid food. Calves are weaned after 6 to 12 months.

While on the reproductive grounds, adult females do not associate with one another. Adult females appear to have habitat preferences in Hawaii. In years without a calf, they are more likely to be observed in waters off the Big Island, but in years with a calf, they are more likely to be seen in Maui [35].

Mature males visit the reproductive grounds to mate. Since the females are dispersed, males cannot monopolize more than one female at a time. Therefore, competition is for a single female rather than multiple females ([10, 20, 22-24, 36-38]. A male will position himself next to an adult female, presumably waiting for an opportunity to mate with her. Some researchers suggest that males could be practicing post-copulatory mate guarding to prevent other males from mating [31]. A male positioned next to the female is termed the “escort”, and may stay with the female for several hours. If another male attempts to take over this position, the two males will proceed through a ritual of dominance displays. The initial defending male is considered the “primary escort” and the challengers, or other males in the group, are referred to as “secondary escorts.” The primary escort will try to intimidate his opponents by performing head lunges, linear bubble trails, and inflating his ventral pleats. He will also chase challengers away and quickly return to the female’s side. If the challenging male is not deterred by the primary escort’s visual threat displays, both males will physically compete for the position.

The challenger may attempt to physically move the primary escort with his body. Competing males can strike each other with their rostrum and powerful tail flukes. These battles can be quite fierce, resulting in bloody tubercles, torn and wounded dorsal fins, and minor physical injuries [22, 28]. Since most males will have many more opportunities to compete for available females, these physical competitions rarely result in death [39]. Competition groups can consist of more than twenty males surrounding a single female. Often times within these groups, the female may solicit competition between males by slapping her pectoral fins on the surface of the water [40]. It has been suggested that some males may work together as a coalition in efforts to displace a principal escort [23]. Occasionally groups may form consisting of only males and are believed to be episodes of dominance sorting between males [23].

Singing is presumed to be a male mating strategy. Humpback whale song has been described as the most complex song in the animal kingdom [41]. Only males sing and rarely is it heard on the feeding grounds [42, 43]. Singers are usually alone, stationary, and canted downward at a 45-degree angle. The format of the song is consistent across populations, although the components of the song may change from year to year [44]. At any one time of the year, all of the whales in an ocean basin are singing the same song. The true function of the whale’s song has plagued researchers for decades. It is unknown why their song continuously changes and which whales are responsible for making such changes. Current hypotheses about their songs include: 1) a way for males to attract females [45-48], 2) a mechanism to synchronize estrus in females [22], 3) and a spacing mechanism for leking males [49]. The mating system of male humpbacks can be described as male dominance polygyny [50]. In this mating system, males are unable to defend multiple females, male parental care is absent, communal display by males occurs, and males engage in direct competition for access to estrus females.

Immature whales (under 5 years of age) [3, 51], may account for forty percent of the population [52] on the wintering grounds. Since young whales are independent by one year of age, it is likely that they learn effective feeding and reproductive behaviors by associating with other whales and through observation.

Song

The length of a humpback whale song can vary, but usually lasts between 14 and 20 minutes. The structural components of the song are quite uniform in all oceans of the world. The song itself can be broken down into four to seven “themes”. Each theme may vary in length, but they are usually produced in the same order. For example, in Hawaii, the 2005 song had four themes. Singers will generally sing all four themes, come to the surface to breath, dive, and repeat themes one to four. Each theme is composed of a phrase that is repeated. Each phrase is made up of one to three unique sounds or “notes.”

It has long been known that humpback whale song changes slightly throughout the breeding season. Why this change is occurring and who is initiating the change has been a mystery. A group of Australian researchers recorded a unique and radical song change from humpback whale singers migrating along the east coast of Australia [53]. Within a matter of two years their song was replaced completely by the song of the Australian west coast population. Further analysis of song recordings revealed this was the result of the introduction of only a small number of west coast whales that migrated down the east coast of Australia. This discovery lends support to the theory that novelty in humpback whale song is indicative of superior fitness and is being selected for by humpback females.

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Food and Foraging

Each summer, humpback whales tend to return to the same feeding grounds, and calves will return to their mother’s feeding area. They feed on euphasids, and a variety of schooling fish such as herring, capelin, and sand lance. Humpbacks are known as “gulpers” [54]. They feed by engulfing large volumes of water, while filtering the prey as the water is pushed back out of the mouth with their tongue [55]. Most whales feed independently, but in some areas, such as in Southeastern Alaska, they are known to feed cooperatively [16, 17, 21]. When feeding, they lunge through schools of prey with their mouth agape. Once their mouth is closed, they use their tongue to push the fish against the baleen plates; by doing this, the water escapes and the food is trapped.

In the Atlantic, primary food sources consist of small schooling fish, including Capelin [8, 16], Herring [56, 57], Makeral [58], and sand lance [59, 60]. In some areas, humpbacks feed exclusively on small shrimp-like euphasiids [61]. Some individual whales are easily recognized due to their unique feeding strategy. They are observed slapping their tail on the water, in order to create bubbles or to stun their prey prior to engulfing it. In the Pacific, where the primary food sources are herring and capelin, some humpbacks are observed agitating the water with lateral motions of their tail, just prior to engulfing their prey. Many of these behaviors appear to be learned [62]. Some whales may also release bubbles through their blowholes to create artificial nets or screens to corral or trap schooling fish [63].

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Status and Conservation

Twentieth century whaling reduced humpback whale populations worldwide from initial estimates approximating 15,000 animals [64], to roughly seven percent of their original numbers [18, 64, 65].

Since the humpbacks protection in the North Pacific in 1966, a research study showed populations increased to approximately 5,000 – 6,000 animals by the end of 1993 [66]. Current population estimates worldwide are approximately 11,570 for the N. Atlantic [67], well over 6,000 for the N. Pacific [66], and over 17,000 for the S. Hemisphere [68]. As a result of being protected, their numbers appear to be growing and the population status is thought to be strong. Current efforts are being made by researchers to obtain a more updated population estimate of the N. Pacific humpback whale population (see SPLASH).

Although protected from intensive commercial whaling, humpback whales still face many threats. These threats include entanglement in nets and fishing gear, boat strikes, habitat degradation, competition for food with commercial fisheries, noise pollution from boat traffic, military sonar, and seismic activities from underwater drilling. If not regulated, whale-watching, a million-dollar industry, may also have negative impacts on the whales [69].

Calf with boat propellar wound, Lahaina, Hawaii, 2005

Predators

Predation on humpback whales is extremely rare [70]. This may be one of the reasons they do not need to form large permanent social groups [16]. Killer whales have been observed on rare occasions to attack a humpback whale [71, 72], and tiger sharks have been observed preying on a dead adult male [73] and a weakened calf separated from its mother. The frequency of teeth marks observed on the body parts of young humpbacks suggests that attacks may be more common on young calves [31].

Hawaii

It is estimated that over 4,000 humpback whales visit Hawai’ian waters each year. This makes Hawaii the primary reproductive grounds for the North Pacific population. This has led to the Hawai’ian Islands Humpback Whale National Marine Sanctuary (HIHWNMS) to help manage and protect this endangered species. Humpback whales within Hawai’ian waters are protected from any aircraft approaching within 1,000 feet, and any boat or person within 100 yards. Those who violate these approach limits are subject to a $25,000 fine.

An appreciation for humpback whales is a growing business in Hawaii, responsible for more than $80,000 annually in tourist income for the state.

Examination of Hawai’ian legends, myths, ceremonies, rituals, petroglyph drawings, historical writings, and the Hawai’ian language, provides little evidence that humpback whales existed in these islands prior to the 19th century [74].

 

Whaling in Hawaii

Hawaii served as an important whaling port to the whaling ships of the North Pacific from 1820 to 1860. Twice a year, whaling ships visited Honolulu and Lahaina to transship their oil and whalebone, and restock on provisions. This created economic growth and jobs in Hawaii.

Although some humpbacks were taken by American whalers operating along the coasts of California and Baja California and in the Western Pacific, most 19th century whaling was focused on the sperm whale and the bowhead whale. In 1840, sperm whale oil sold for $1.00/gal compared to only 30 cents/gal for oil rendered from humpback blubber [75]. Although sperm whales were present in the Hawai’ian waters, American whalers exploited richer sperm whale grounds elsewhere in the North Pacific [76]. In 1847, an attempt to establish a shore station to take whales locally proved to be unsuccessful. In the 1850s, additional shore stations were developed near Lahaina in attempts to lure whaling ships away from Honolulu. However, the discovery of petroleum in 1859 caused the demand for whale oil to decline significantly. This led to the demise of the shore stations by the end of 1860s.

It wasn’t until around 1920 and during the early sixties that whalers ventured into the summer feeding grounds of the North Pacific, killing significant numbers of whales. During the 1962 and 1963 seasons, International Whaling Statistics (1966) report that Russian whalers killed over 3,400 humpbacks in their summer feeding grounds [77]. This massive killing led to the complete ban on the taking of humpback whales in the North Pacific.

Protection

In 1946, an international committee known as the International Whaling Commission (IWC), formed to manage the whaling industry and help establish sustainable stocks. Initially unsuccessful, the IWC expanded its role during the sixties to include a strong conservation ethic. It wasn’t until 1986, when the IWC instituted a 10-year moratorium, or complete ban, on commercial whaling. Certain nations including Iceland, Norway, and Japan are dissatisfied with the moratorium, as they wish to continue hunting some species of whales as a source of food and oil.

Presently under the IWC moratorium two types of whaling are permitted: 1) subsistence whaling, and 2) scientific whaling. Subsistence whaling involves the taking of a limited number of whales by certain indigenous or native people, for their own use. Scientific whaling refers to the regulated taking of whales not considered threatened or endangered, such as the Minke whale, for the purpose of furthering our knowledge about whales.

It is estimated that nearly 15,000 humpbacks existed in the North Pacific prior to 1900 (Rice, 1977) and were reduced to less than 1,000 around 1960 (Herman and Antinoja, 1977). Humpback whales were first protected in the North Atlantic in 1956 and later protected in the North Pacific in 1966. This species was further protected by the marine mammal protection act of 1972, and the endangered species act of 1973.

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