Order Cetacea • Family Balaenopteridae
Megaptera novaeangliae (Borowski)
The humpback whale is a medium-sized baleen whale of the rorqual family, which is characterized by ventral throat grooves. When fully grown, humpbacks are typically 14 to 15 meters long, weighing 30 to 40 metric tons. Females are slightly longer and larger than males, on average. The most distinguishing characteristic of the humpback whale is the long (5 meters) narrow pectoral fins. The ventral side of the pectoral fin is always white, but the dorsal side can be white, black, or anywhere in between.
Another unique feature of the humpback whale is the presence of numerous knobby structures, or "tubercles," on the snout and chin. Each tubercle contains a sensory hair. Humpback whales are known for their aerial behavior, breaching, leaping from the water or slapping their tail or flippers on the surface of the water more often than other whales. The humpback is easily identified in Hawai‘i during the winter because it is the only large whale commonly found in nearshore waters.
Annual Migratory Cycle
In winter, North Pacific humpback whales congregate on a few centralized breeding areas (Hawai‘i, Mexico, Central America and Japan) for activities related to mating and calving. The whales migrate from geographically dispersed, matrilineal feeding areas around the Pacific Rim including the coastal waters of California, Alaska and Russia, as well as the Bering Sea. Humpback whales typically start arriving in the Hawai‘i wintering area in November, with peak densities occurring in February and March. They remain in large numbers until late spring when they migrate out of Hawai‘i, heading toward their high-latitude feeding grounds. The shortest migration from Hawai‘i to Alaska would be approximately 3,000 miles, which takes the whale a minimum of about 36 days.
Humpback whales occur in all oceans of the world. Once they have arrived on the Hawaiian wintering grounds, they are primarily coastal, with the majority found inside the 100-fathom contour, and concentrated in leeward, sheltered waters. Acoustic methods have found singing humpbacks out to 15 kilometers from shore. Recent visual vessel surveys have also confirmed the sightings of humpback whales out to the 1000-fathom isobath. This offshore distribution may result in part from local inter-island and oceanic migration.
Humpback whales are found throughout all of the main Hawaiian Islands. In general, whales in Hawai‘i appear to be fairly mobile, commonly visiting more than one of the islands and spending relatively little time in a single area. Researchers identifying individual whales typically re-sight only about 10% of them more than once in an area in a single year. Some whales are re-sighted over periods of a few days or weeks. It is possible that the longer intervals result from a whale leaving an area and then returning.
Humpback whale swimming speed and patterns vary between different behavioral and social classes. Lone male singers tend to be solitary and are either stationary or moving at very low speeds (< 1 km/h). Mothers and calves may alternate resting and swimming with average speeds of 2-3 km/h. Small pods of adults typically swim at 4-5 km/h and large, surface-active pods can swim at speeds up to 20 km/h.
Humpback whales once numbered an estimated 15,000 in the North Pacific. Heavy whaling reduced their numbers in the early and mid 1900’s. Researchers use the distinctive markings and shape of the tail flukes to identify individual humpback whales over the course of many years. The longest sighting histories in the North Pacific are upwards of 30 years. A mark-recapture study using sightings and re-sightings of individually identified whales indicated a population size between 1,437 and 2,100 in Hawaiian waters in the 1980's. By 1997, a similar study indicated the statewide population was probably between 3,000 and 4,000 individuals corroborating aerial surveys that indicated an annual population growth rate of approximately 8%.
Diving behavior in humpbacks is highly variable. At one extreme are singers who routinely dive for approximately 18 minutes, and then spend less than 1 minute on the surface. At the opposite extreme are mothers and calves that may be seen "logging" or resting on the surface for hours at a time. The average dive times range from 5 to 10 minutes, with 1 to 2 minutes at the surface. As pod size increases, the pod tends to spend less time below and more time on the surface.
Humpback males are famous for their wintertime singing, although its functions remain unclear. Songs are typically 15 to 18 minutes in length, and range from < 20 Hz to at least 8 kHz. Broadband source levels are at least 169 dB re 1 µPa and probably greater. Songs are produced only by males, and only a fraction of males sing at any given time. Surface active or competitive groups produce "social sounds", which range from 100 Hz to 1 kHz. To date, no vocalizations have been recorded from females in Hawai‘i, although they are thought to produce feeding calls in Alaska. Observers have reported hearing "high-frequency, squeaky calls" in the presence of mothers
Because of their size, no audiogram has been produced for humpback whales. However, information about their hearing range can be inferred from two sources: The spectral range of their own vocalizations and an anatomical examination of their cochlea. Humpback song is known to range from at least 20 Hz to at least 8 kHz. For perspective, humans hear between 20 Hz and 20 kHz.
Humpback whales are a migratory species that essentially divides life between feeding in high latitude waters (e.g., Alaska) and engaging in reproductive activities in low-latitude waters (e.g., Hawai‘i). However, there have been unpublished observations of humpbacks feeding in Hawai‘i. Humpback whales primarily eat small schooling fish such as herring, capelin, sand lance, as well as euphausiid crustaceans, better known as "krill". Because they are baleen whales, humpbacks feed by engulfing entire schools of their prey, and expel the unwanted seawater through their baleen plates before swallowing.
Humpbacks and other species of whales were severely reduced by commercial whaling in the twentieth century. In recent years, studies have shown that the North Pacific population is beginning to increase in size, but has not yet reached pre-exploitation levels.
Humpback whales are occasionally trapped in fishing gear. Potentially more serious, a number of whales are struck and sometimes killed by vessels operating in Hawaiian waters.
Humpback whales alter their behavior in response to vessel traffic. The recent observations of population increase indicate that these short-term behavioral responses to vessels are not detrimental enough to prevent recovery. Vessels have been implicated in the offshore movement of mothers and calves off West Maui. Another study examined all pod types and found no change in distribution.