Northern right whale dolphins (Lissodelphis borealis) are endemic to the waters of the North Pacific Ocean. On the eastern coast of Asia, they are found from Paramushir Island, Russia to Cape Nojima, Japan. On the western coast of North America, they have been documented from Vancouver Island, Canada to Baja California, Mexico. Multiple entanglements in high seas driftnets confirmed their presence across the North Pacific Ocean. A few sightings have occurred outside their typical range including the Gulf of Alaska and near the Aleutian Islands. (Bjorge, et al., 1992; Jefferson and Newcomer, 1993; Kajimura and Loughlin, 1988; Leatherwood and Walker, 1979; Nishiwaki, 1967)
Northern right whale dolphins most commonly inhabit deep offshore and continental waters. However, they are occasionally observed near the coast, particularly where undersea geographic features create deep waters close to shore. They prefer cool waters, and are most often sighted in waters ranging in temperature from to 7.8° to 18.9° C. (Bjorge, et al., 1992; Jefferson and Newcomer, 1993; Jefferson, et al., 1994a; Leatherwood and Walker, 1979)
This species has been documented migrating south and inshore during the winter months, and north and offshore during the summer months. Within their eastern range, specifically California, they are sighted inshore in the fall months; they increase in numbers until mid-winter, and then decrease towards the late spring and early summer. In their western range, off the coast of northern Honshu, Japan, northern right whale dolphins have only been reported during non-summer months. The reasons for these seasonal movements are largely unknown; however, changes in water temperature could be a factor. In the fall, northern right whale dolphins move toward the cooling waters of the California coast and withdraw in the spring/summer as they warm. Another possible influence could be prey abundance. In California, the maximum abundance of northern right whale dolphins correlates with the maximum abundance of an important prey item, California market squid. (Forney and Barlow, 1998; Jefferson and Newcomer, 1993; Kasuya, 1971; Leatherwood and Walker, 1979)
Northern right whale dolphins have a mostly black body. However, they possess a white stripe that begins at their throat, widens in the thoracic region and continues as a thin band that terminates at the fluke notch. Compared to males, females have wider white markings around their urogenital region. Both males and females possess a white mark behind the tip of their lower jaw. The dorsal side of their flukes are predominantly light grey and primarily white on the ventral side. Variation in color does occur, typically in the area covered by the white ventral markings. Some common variations from the normal coloration include the white ventral strip extending up the edges of the body, white coloration of nearly the whole lower jaw, a white smudge on the side of the melon and beak and variation in the amount of white coloration on the flippers. (Baird and Stacey, 1991; Baird and Stacey, 1993; Jefferson and Newcomer, 1993; Jefferson, et al., 1994a; Jefferson, et al., 1994b; Leatherwood and Walker, 1979; Okada and Hanaoka, 1940)
A peculiar feature of northern right whale dolphins is their lack of a dorsal fin; they are the only dolphin species in the North Pacific Ocean without one. Another diagnostic characteristic of this species is its slender, elongated caudal peduncle. They possess a straight mouth line and a short, yet distinct beak. Their flippers are slightly curved with pointed tips. Their flukes possess a concave posterior margin and a deep central notch. Both their flippers and flukes look disproportionately small compared to their body. Overall, they possess a very streamlined shape. (Baird and Stacey, 1993; Jefferson and Newcomer, 1993; Jefferson, et al., 1994a; Jefferson, et al., 1994b; Leatherwood and Walker, 1979)
Their maximum known weight is 115 kg. The mean length of males aged 12 and older is 237.9 cm, while the largest male measured was 307.0 cm long. The mean length of females aged 12 or older is 211.2 cm. No females over 230 cm have been collected. Males appear to reach greater maximum lengths than females. (Ferrero and Walker, 1993; Jefferson and Newcomer, 1993; Jefferson, et al., 1994b; Leatherwood and Walker, 1979)
Their teeth are cone shaped, small, slender and sharp. There is great variation in the dental formula and number of teeth possessed by individuals of this species. Each side of the upper jaw holds 37 to 52 teeth, with 42 to 54 teeth on each side of the lower jaw. They can have 158 to 212 teeth total. (Baird and Stacey, 1991; Baird and Stacey, 1993; Jefferson and Newcomer, 1993; Jefferson, et al., 1994a; Jefferson, et al., 1994b; Leatherwood and Walker, 1979; Okada and Hanaoka, 1940)
Calves achieve their adult colorations at approximately one year. Before this, they are a paler version of the adult coloration, consisting predominantly of browns, greys and creams. (Baird and Stacey, 1991; Jefferson and Newcomer, 1993; Leatherwood and Walker, 1979)
Currently, nothing is known about the mating system of northern right whale dolphins.
Little is known about the reproduction of northern right whale dolphins. The minimum calving interval is estimated to be two years, because their gestation period is estimated at over 12 months and because of the lack of ovarian activity in a sample of females who were presumed to have given birth at least one year prior. Their gestation period is estimated to be 12.1 to 12.3 months. Calving appears to peak in July and August. Ferrero and Walker (1993) calculated mean lengths at birth to be 99.7 to 103.8 cm. The duration of lactation remains unknown. The average age of sexual maturity for females is estimated to be 9.7 to 10.4 years, when their body length is approximately 199.8 to 201.1 cm. The average age of sexual maturity among males is estimated to be 9.9 to 10.1 years. Testis mass changes little with age until the onset of sexual maturity, when it then increases rapidly. Mature testis masses range from 117.4 to 1,300 g. (Ferrero and Walker, 1993)
Currently, nothing is known about the parental investment of northern right whale dolphins.
There is very little information available regarding the lifespan of northern right whale dolphins. However, the live-capture fishery has taken two live specimens. One died three days after its introduction into an acclimation pool. The autopsy and histopathology examinations determined the cause of death was linked to stress. The second lived 15 months in a 540,000 gallon display tank. The cause of death for this individual was never determined. (Walker, 1975)
Northern right whale dolphins are very social. Off the eastern Pacific coast, the average pod size is 110 individuals, while off the western Pacific coast, they have an average pod size of 200 individuals. They have also been periodically observed alone. (Jefferson and Newcomer, 1993; Jefferson, et al., 1994a; Leatherwood and Walker, 1979)
Individuals swimming slowly generally only expose small portions of their head, mainly the blowhole, to breath. Fast swimming individuals may either swim close to the surface, surfacing rapidly to breathe or swim swiftly at the surface with low angle leaps. Northern right whale dolphins have also been seen performing belly flops, fluke slaps and side slaps. Individuals have been observed breathing at intervals of 10 to 75 seconds, and entire pods have been noted to dive for a maximum of 6.15 minutes. They have been reported to swim at speeds up to 34 km per hour. (Au and Weihs, 1980; Jefferson, et al., 1994a; Leatherwood and Walker, 1979)
Northern right whale dolphins generally occur in one of four different pod configurations. The first configuration is densely packed groups lacking distinct subgroups. The second consists of noticeably distinct subgroups of varying numbers of individuals. Third, is a v-shaped formation and fourth is a line formation. When northern right whale dolphins are in the company of other cetacean species, they typically maintain small, tightly packed groups. They will, however, form mixed interspecific pods with Pacific white-sided dolphins. (Jefferson, et al., 1994a; Leatherwood and Walker, 1979)
This species exhibits remarkably variable behavior towards boats. They may vigorously avoid them or they may approach and interact with them. Bow riding more readily occurs in the presence of other cetacean species, such as Pacific white-sided dolphins. (Jefferson and Newcomer, 1993; Jefferson, et al., 1994a; Leatherwood and Walker, 1979)
Northern right whale dolphins are frequently documented interacting with other marine mammal species. They are most commonly associated with Pacific white-sided dolphins; they have also been seen with common bottlenose dolphins, short-beaked common dolphins, striped dolphins, Risso's dolphins, Dall's porpoises, short-finned pilot whales, fin whales, sei whales, humpback whales, grey whales and California sea lions. (Baird and Stacey, 1991; Baird and Stacey, 1993; Ferrero, et al., 2002; Jefferson, et al., 1994a; Leatherwood and Walker, 1979; Leatherwood, 1974; Wilke, et al., 1953)
All documented strandings have been of single individuals, and no mass strandings have been ever reported. Typically, only a few individual strandings occur each year. The exception was in 1981, where approximately 23 northern right whale dolphins were stranded on southern and central California beaches for undetermined reasons. Strandings have been mainly linked with pathological conditions caused, or irritated by parasites. (Baird and Stacey, 1991; Cowan, et al., 1986; Jefferson and Newcomer, 1993; Leatherwood and Walker, 1979)
There is currently no information available regarding the home range size of northern right whale dolphins.
Northern right whale dolphins primarily communicate with clicks and pulsed vocalizations. Unlike other dolphin species, they do not produce whistles. A commonly produced sound is a burst-pulse series. Burst-pulse series consist of 6 to 18 individual burst-pulse units. Eight unique burst-pulse series have been documented, and most series are repeated in sequence. Compared to echolocation clicks, burst-pulse vocalizations are lower in frequency and shorter in duration. It is believed that these burst-pulse vocalizations may play a comparable role in communication to the conventional whistles emitted by other delphinid species. (Rankin, et al., 2007)
Northern right whale dolphins prey primarily on mesopelagic fish and squid. They dive to depths of at least 200 m in search of food. (Chou, et al., 1995; Jefferson and Newcomer, 1993; Chou, et al., 1995; Fitch and Brownell, 1968; Jefferson and Newcomer, 1993)
Chou, Bright and Yeh (1995) examined the stomach contents of two northern right whale dolphins. They determined that fish are a major component of their diet, comprising 89% of their stomach contents. Lanternfish were the most abundantly occurring fish group, comprising 89% of their fish prey. The most common fish species found were brokenline laternfishes and Warming's lanternfishes. Squid are a smaller component of their diet, comprising 11% of their stomach contents. The most common squid species found were Boreopacific armhook squid and Abraliopsis felis. (Chou, et al., 1995)
Walker and Coe (1989) documented foreign body ingestion in two specimens from Santa Monica and Los Angeles, California. They discovered fronds of marine plants, a honey bee, white bird feathers, a partial plastic bag, several small pieces of blue vinyl plastic and a rusted metal bottle cap inside individual. (Jefferson and Newcomer, 1993; Jefferson and Newcomer, 1993; Walker and Coe, 1989)
Northern right whale dolphins host several species of internal parasites; Nasitrema species in their brain and air sinuses, Crassicauda species in their inner ear complex and air sinuses, Anisakis simplex in their stomach, Monorygma grimaldii in their peritoneal cavity, Phyllobothrium delphini in their blubber, and Sarcosporidia in their skeletal muscles. External parasites of northern right whale dolphins include barnacles, such as Xenobalanus species, and copepods including Penella and Nasitrema species, which are thought to cause major damage to their brain and air sinuses and may play a role in their strandings and death. The effects of most parasites are largely unknown, but heart scars, lung abscesses and inflammation, pulmonary oedema, gastric ulceration, mucosal ulceration and brain lesions were reported in some of the stranded specimens. (Cowan, et al., 1986; Dailey and Walker, 1978; Jefferson and Newcomer, 1993; Jefferson, et al., 1994a)
Northern right whale dolphins are occasionally captured by Japanese small cetacean whalers for food, oil, leather and fertilizers. Their flesh, heart, liver and kidneys are consumed, their blubber provides oil, their hide is tanned into low grade leather and their skeleton and other viscera are used as fertilizer. (Robards and Reeves, 2011; Wilke, et al., 1953)
Northern right whale dolphins feed on commercially important squid species. They are known to occur in areas frequently used by commercial fisherman, and could possibly be seen as competition. (Leatherwood and Walker, 1979)
Mangel (1993) has estimated a mean population size of 247,000 individuals in the North Pacific, with a 95% confidence interval of 61,000 to 1,004,000 individuals. However, it should be noted that the lower limit (61,000 individuals) is believed to be biologically unreasonable. (Mangel, 1993)
The main threat to northern right whale dolphins was the large scale pelagic driftnet fishery that operated out of Japan, Korea and Taiwan. Dolphins would become entangled in driftnets set for squid, and drown. Entangled individuals were occasionally freed, but future survival was unlikely due to the injuries commonly sustained during entanglement. These injuries could include fishing gear still attached to the animal that could impair their movements or ability to eat, ingestion of hooks, open bodily wounds, and damage or loss of fins. The entanglements in driftnets were typically greatly clustered, possibly resulting in entire pods, families or other reproductive units being killed at once. Between 1985 to 1990, this fishery was estimated to kill 15,000 to 20,000 individuals each year. It was estimated that the 1978 pre-exploited population has been reduced by 24 to 73% by this fishery. In 1993, the United Nations suspended the use of large-scale pelagic drift nets, halting the slaughter of this species and many others. (Bjorge, et al., 1992; Carretta, et al., 2003; Ferrero and Walker, 1993; Jefferson and Newcomer, 1993; Jefferson, et al., 1994b; Mangel, 1993)
Northern right whale dolphins are one of the most commonly entangled marine mammals species in the California drift gillnet fishery, targeting broadbill swordfishes and common thresher sharks. From 1996 to 2002, the observed mortality for this species was 31 individuals; however, the estimated mortality was 151 individuals. Due to the fact the data used to calculate this mortality estimate did not include any deaths or injuries not directly observed by researchers, it represents only a minimum estimate of mortality. Despite fishermen being required to report any interactions with marine mammals, it is highly probable the vast majority of interactions went undocumented. (Carretta, et al., 2003)
Northern right whale dolphins have never been subject to extensive direct hunting, however, Japanese small cetacean whalers infrequently take them. They are typically killed with buckshot fired from shotguns and/or harpoons. A single company slaughtered 465 off the coast of Japan in May and June of 1949. (Jefferson and Newcomer, 1993; Wilke, et al., 1953)
Michelle Pasnak (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
A substance that provides both nutrients and energy to a living thing.
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
found in the oriental region of the world. In other words, India and southeast Asia.
An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).
an animal that mainly eats fish
mainly lives in oceans, seas, or other bodies of salt water.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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