Bowhead Whale

The **bowhead whale** (*Balaena mysticetus*) is a species of the right whale family Balaenidae, in suborder Mysticeti, and genus *Balaena*. A stocky dark-colored whale without a dorsal fin, it can grow 14 m (46 ft) to 18 m (59 ft) in length. This thick-bodied species can weigh from 75 tonnes (74 long tons; 83 short tons) to 100 tonnes (98 long tons; 110 short tons). They live entirely in fertile Arctic and sub-Arctic waters, unlike other whales that migrate to low latitude waters to feed or reproduce. The bowhead was also known as the **Greenland right whale** or **Arctic whale**. American whalemen called them the **steeple-top**, **polar whale**, or **Russia** or **Russian whale**. The bowhead has the largest mouth of any animal. The bowhead was an early whaling target. The population was severely reduced before a 1966 moratorium was passed to protect the species. Through conservation efforts, the bowhead population has since recovered and is now rated "Least Concern" on the IUCN Red List of Threatened Species.

## Description

The bowhead whale has a large, robust, dark-colored body and a white chin/lower jaw. The whale has a massive triangular skull, which the whale uses to break through the Arctic ice to breathe. Inuit hunters have reported bowheads surfacing through 60 cm (24 in) of ice. The bowhead also has a strongly bowed lower jaw and a narrow upper jaw. Its baleen is the longest of that of any whale, at 3 m (9.8 ft), and is used to strain tiny prey from the water. The bowhead whale has paired blowholes, at the highest point of the head, which can spout a blow 20 feet high. The whale's blubber is the thickest of that of any animal, with a maximum of 43–50 cm (17–20 in). Unlike most cetaceans, the bowhead does not have a dorsal fin.

Bowhead whales are comparable in size to the three species of right whales. According to whaling captain William Scoresby, Jr., the longest bowhead he measured was 17.7 m (58 ft) long, while the longest measurement he had ever heard of was of a 20.4 m (67 ft) whale caught at Godhavn, Greenland, in early 1813. He also spoke of one, caught near Spitsbergen around 1800, that was allegedly nearly 21.3 m (70 ft) long. In 1850, an American vessel claimed to have caught a 24.54 m (80.5 ft) individual in the Western Arctic. It is questionable whether these lengths were actually measured. The longest reliably measured lengths of the sexes were 16.2 m (53 ft) in a male and 18 m (59 ft) in a female, both killed by humans and landed in Alaska.[17] On average, female bowheads are larger than males.

Analysis of hundreds of DNA samples from living whales and from baleen used in vessels, toys, and housing material has shown that Arctic bowhead whales have lost a significant portion of their genetic diversity in the past 500 years. Bowheads originally crossed ice-covered inlets and straits to exchange genes between Atlantic and Pacific populations. This conclusion was derived from analyzing maternal lineage using mitochondrial DNA. Whaling and climatic cooling during the Little Ice Age, from the 16th century to the 19th, is supposed to have reduced the whales’ summer habitats, which explains the loss of genetic diversity.

A 2013 discovery has elucidated the function of the Bowhead's large palatal retial organ. The bulbous ridge of highly vascularized tissue, the *corpus cavernosum maxillaris*, extends along the center of the hard plate, forming two large lobes at the rostral palate. The tissue is histologically similar to that of the corpus cavernosum of the mammalian penis. It is hypothesized that this organ provides a mechanism of cooling for the whale (which is normally protected from the cold Arctic waters by 40 cm or more of fat). During physical exertion, the whale must cool itself to prevent hyperthermia (and ultimately brain damage). It is now believed that this organ becomes engorged with blood, causing the whale to open its mouth to allow cold seawater to flow over the organ, thus cooling the blood.

## Behavior

### **Swimming**

Bowhead whales are not social animals, typically traveling alone or in small pods of up to 6. They are able to dive and remain submerged underwater for up to an hour. However, the time spent underwater in a single dive is usually limited to 9-18 minutes. Bowheads are not thought to be deep divers but they can reach a depth of up to 500 feet. These whales are slow swimmers, normally traveling at about 2–5 km/hr. When fleeing from danger, they can travel at a speed of 10 km/hr. During periods of feeding, the average swim speed is reduced to 1.1 – 2.5 m/s.

### **Feeding**

The head of the bowhead whale comprises a third of its body length, creating an enormous feeding apparatus. Bowhead whales are filter feeders, feeding by swimming forward with its mouth wide open. The whale has hundreds of overlapping baleen plates consisting of keratin hanging from each side of the upper jaw. The mouth has a large upturning lip on the lower jaw that helps to reinforce and hold the baleen plates within the mouth. This also prevents buckling or breakage of the plates from the pressure of the water passing through them as the whale advances. To feed, water is filtered through the fine hairs of keratin of the baleen plates, trapping the prey inside near the tongue where it is then swallowed. The diet consists of mostly zooplankton which includes copepods, amphipods, and many other crustaceans. Approximately 2 tons of food is consumed each day. While foraging, bowheads are solitary or occur in groups of two to ten or more.

### **Vocalization**

Bowhead whales are highly vocal and use low frequency (<1000 Hz) sounds to communicate while traveling, feeding, and socializing. Intense calls for communication and navigation are produced especially during migration season. During breeding season, bowheads make long, complex, variable songs for mating calls.

### **Reproduction**

Sexual activity occurs between pairs and in boisterous groups of several males and one or two females. Breeding season is observed from March through August; conception is believed to occur primarily in March when song activity is at its highest. Reproduction can begin when a whale is 10 to 15 years old. The gestation period is 13–14 months with females producing a calf once every three to four years. Lactation typically lasts about a year. To survive in the cold water immediately after birth, calves are born with a thick layer of blubber. Within 30 minutes of birth, bowhead calves are able to swim on their own. A newborn calf is typically 4-4.5 m (13.1-14.7 ft) long, weighs approximately 1,000 kg (2,200 lb), and grows to 8.2 m (27 ft) within the first year.

## Health

### **Lifespan**

Bowhead whales are known to be the longest-living mammals, living for over 200 years. In May 2007, a 15 m (49 ft) specimen caught off the Alaskan coast was discovered with the head of an explosive harpoon embedded deep under its neck blubber. The 3.5-inch (89 mm) arrow-shaped projectile was manufactured in New Bedford, Massachusetts, a major whaling center, around 1890, suggesting the animal may have survived a similar hunt more than a century ago. This whale was estimated to be 211 years old. Other bowhead whales found on the whaling expedition were estimated to be between 135 and 172 years old. This discovery showed the longevity of the bowhead whale is much greater than originally thought.

### **Genetic Causes**

It was previously believed the more cells present in an organism, the greater the chances of mutations that cause age related diseases and cancer. Although the bowhead whale has thousands of times more cells than other mammals, the whale has a much higher resistance to cancer and aging. In 2015, scientists from the US and UK were able to successfully map the whale's genome. Through comparative analysis, two alleles that could be responsible for the whale's longevity were identified. These two specific gene mutations linked to the bowhead whale's ability to live longer are the ERCC1 gene and the proliferating cell nuclear antigen (PCNA) gene. ERCC1 is linked to DNA repair as well as increased cancer resistance. PCNA is also important in DNA repair. These mutations enable bowhead whales to better repair DNA damage, allowing for greater resistance to cancer. The whale's genome may also reveal physiological adaptations such as having low metabolic rates compared to other mammals. Changes in the gene UCP1, a gene involved in thermoregulation, can explain differences in the metabolic rates in cells.

## Ecology

### **Range and Habitat**

The bowhead whale is the only baleen whale to spend its entire life in the Arctic and sub-Arctic waters. The Alaskan population spends the winter months in the southwestern Bering Sea. The group migrates northward in the spring, following openings in the ice, into the Chukchi and Beaufort seas. It has been confirmed the whale's range varies depending on climate changes and on the forming/melting of ice.

### **Population**

The bowhead population around Alaska has increased since commercial whaling ceased. Alaska Natives continue to kill small numbers in subsistence hunts each year. This level of killing (25–40 animals annually) is not expected to affect the population's recovery. The population off Alaska's coast (the Bering-Chukchi-Beaufort stock) appears to be recovering and was at about 10,500 animals as of 2001. The status of other populations is less well known. There were about 1,200 off West Greenland in 2006, while the Svalbard population may only number in the tens. However, the numbers have been increasing in recent years. In March 2008, Canada's Department of Fisheries and Oceans stated the previous estimates in the eastern Arctic had under-counted, with a new estimate of 14,400 animals (range 4,800–43,000). These larger numbers correspond to prewhaling estimates, indicating the population has fully recovered. However, if climate change substantially shrinks sea ice, these whales could be threatened by increased shipping traffic.