Gray's beaked whale
Gray's beaked whale (scientific name: Mesoplodon grayi ) is one of 21 species of beaked whales (Hyperoodontidae or Ziphiidae), medium-sized whales with distinctive, long and narrow beaks and dorsal fins set far back on their bodies. found in the Southern Hemisphere, they are marine mammals within the order of cetaceans.
"This species was described from the remains of animals found at a mass stranding involving approximately 28 whales in the Chatham Islands off New Zealand in 1874. It was described in 1876 by von Haast, and named after the former Director of the British Museum, John E. Gray, who had died the year before. (Gray had described no less than three new species of beaked whale during his career: Hector's, the Strap-toothed and the Spade-toothed beaked whale.) (Australian Museum)
Some general physical features common to all beaked whales are endothermic metabolism and bilateral symmetry. Gray’s Beaked whales, like all members of Ziphiidae, are medium sized whales with a distinct beak. They are 5.0 to 6.0 meters in length and have a body mass of approximately five tons (10,000 pounds).
One of the most conspicuous features of members of the genus Mesoplodon is the single pair of enlarged triangular tusks in the lower jaw. The location of these tusks is set farther back in the mouth than in other beaked whales. The exact function of these tusks is unknown, but the pattern of scarring on the head and body of examined individuals indicates that fighting may occur, most likely for mates. Some Mesoplodon have a hardened bone in their skulls, acting like a shield while fighting. These tusks were originally thought to erupt only in males. However, more recent information shows that the tusks erupt in both sexes. In any case, there is thought to be no sexual dimorphism other than the possibility of this ornamentation. Beached females with erupting tusks, have been discovered recently with high frequency. (Culik, 2002; MacLeod, 2000; MacLeod, 2002)
Gray’s Beaked whale is distinct from all other beaked whales (except for Shepherd's beaked whale) in that it does not lack upper teeth; rather, it has a row of 17 to 22 teeth lining each side of the upper jaw. (Culik, 2002; Evans, 1987; Klinowska and Cooke, 1991; MacLeod, 2000; MacLeod, 2002)
The coloration pattern of Gray’s Beaked whales is similar to other beaked whales, with dark brown to gray on the back and flanks, and light gray to white on the underside. The beak is characteristically white or light colored with white flecks extending to the throat. There are also conspicuous white markings around the navel, genitals, and anal regions. (Culik, 2002; Evans, 1987; Klinowska and Cooke, 1991; MacLeod, 2000; MacLeod, 2002)
Key general behaviors of the species are: natatorial ; diurnal ; motile ; migratory ; and social. Pods of Gray’s Beaked whales have been spotted in the waters throughout the Southern Hemisphere, but there is no information on the movements of particular pods or individuals. No attempts to track or radio-collar these animals have been reported. (Klinowska and Cooke, 1991)
Recorded sightings of Gray's beaked whales are usually pods of between four and ten of these mammals. Some authorities indicate that these animals may form larger pods than other beaked whales, and mass strandings of 28 animals have been noted. Single animals have been observed, but they are rare. There have been many unconfirmed reports that Gray’s Beaked whale raises its white beak above the water just prior to surfacing. (Culik, 2002; Evans, 1987)
Vocalizations and Communication
The communication habits of Gray’s Beaked whale are unknown, but those of other whales have been well studied. Whales are famous for their combination of songs, squeals, grunts, clicks, and clacks. Because water serves as a much better transmission medium for sound than air, evolution has clearly centered on vocal communication rather than any other form. The timing of whale communications, along with their content, may signal position, identity, threats, or food to other members of a pod or to other pods. (Evans, 1987)
The most common beaked whales, Blainville's Beaked whales, have been observed to use particular patterns of clicks when herding schools of prey, possibly to confuse them. It has been proposed that Gray’s Beaked whale uses similar methods, but further information is unavailable. (Evans, 1987)
Some tactile communication most likely occurs between mates, as well as between mothers and their offspring. If the tusks of these animals are used in physical competition, as scarring patterns on the head indicate, this is another form of tactile communication which should be noted. (Evans, 1987) Other communication channels are tactile and chemical; in particular, the female may signal sexual readiness with chemical cues. Some of the acoustical communication is thought to occur in choruses. In addition to using all of the above channels for perception and communication, visual perception is utilized to evaluate the environment.
There is virtually no information on the lifespan of Gray’s Beaked whale, and there have been no reports of attempts to keep any of this species in captivity. (Klinowska and Cooke, 1991)
General reproductive features of the species are: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); and viviparous. Unfortunately, there is little information on the mating system of Gray’s Beaked whale. However, it is very likely that Gray’s Beaked whale follows similar patterns to other toothed whales (Odontoceti). Gray’s Beaked whale, like other toothed whales, does not show as distinct a seasonality in mating and birth as do the baleen whales; this is primarily due to the relatively warmer waters that toothed whales inhabit.
Toothed whales live in small groups with very large ranges of thousands of square miles. It may be difficult for individuals to meet others of the opposite sex, so when they do, it is essential that the right signals are conveyed. Toothed whales are very social, and when pods meet there are physical changes in the female’s body to indicate to potential mates that she is ready. Though these exact signals are unknown, it is likely that a combination of both behavioral dance-like movements and hormones discharged through feces or urine serve as cues. (Evans, 1987)
The courtship and mating rituals usually involve belly contact between the male and female. The pair may be interlocked vertically, or the male may swim upside-down underneath the female. There is also much play in the form of chases, breaching of the surface, and flipper contact. All these behavioral cues convey the readiness to mate. (Evans, 1987)
The mother most likely give birth to a single calf. Gray’s beaked whales, like many whales, are most often seen in pods and highly social behavior has been observed. Often in these groups, females that don't have offspring of their own assist other females in the pod raise their calves. A calf likely remains by its mother’s side until it reaches maturity. (Evans, 1987)
Although toothed whales occupying warm oceanic waters can breed throught the year, most breeding in the southern hemisphere is probably between October and December, and the young are born between February and March. Breeding grounds for similar species are often in shallower waters that are sheltered by bays or inlets. Seasonal movements from winter mating grounds to summer feeding grounds are common for other species but not confirmed for Gray’s Beaked whale. (Evans, 1987)
All cetacean species follow a similar pattern for parental investment. The mother nurses the young; she and the pod family teach newborn calves how to socialize, how to avoid preadators, and how to hunt. Specific information on Gray’s Beaked whale is unavailable. (Evans, 1987)
Distribution and Movements
The general distribution of Gray's beaked whales, Mesoplodon grayi, is in the oceans of the southern hemisphere, south of 30 degrees latitude.
Original sightings were off the coast of New Zealand and Eastern Australia east to Argentina and Chile. However, recent sightings near South Africa, north to Madagascar, and in the Indian Ocean east to Australia confirm its circumpolar home range.
There has been one confirmed live animal sighting in the northern hemisphere, off the coast of The Netherlands, but there have been no other indications of a North Atlantic population (IUCN, 1991). Thus is therefore considered an "extralimital occurrence."
Animals are generally spotted in waters deeper than 2000 meters, but the species also frequents shallower waters and have often been found beached in New Zealand. (Klinowska and Cooke, 1991)
Beaked whales of the genus Mesoplodon eat squid almost exclusively, usually members of the families Ommastrephidae, Octopoteuthidae, Enoploteuthidae, and Neoteuthidae. This carnivore may also feed on deep-sea and mesopelagic zone fish (Lampanyctus, Scopelogadus, Cepola) as well as certain mollusks (sometimes labelled a molluscivore), but is likely to seek only opportunistic prey; some researchers think that squid make up the great majority of the diet. (Evans, 1987)
The evolutionary development of dentition in mesoplodont whales and their nearly exclusive diet of squid, indicate that there must be a strong ecological relationship between these organisms. The highly specialized tongue and reduced teeth allow the whales to use suction to capture their prey. The stomach remains of mesoplodont whales almost always contains squid species smaller than 500 g, which contrasts sharply with other beaked whales (genera Hyperoodon and Ziphius) whose diet consists mainly of squid averaging 1000 g in weight (CMS, 2003). This information indicates that Mesoplodon occupies a dietary niche separate from other beaked whales. The preference for and effectiveness at capturing squid suggests that mesoplodont whales strongly impact the squid population.
Natural preadators of Gray's Beaked whales are unknown. The natural coloration pattern (dark on the dorsal side, lighter on the belly) makes these animals difficult to see from above (where they blend in with darker water below) and from below, where they blend in with lighter water above. (Klinowska and Cooke, 1991)
This species is not known to be commercially hunted, but the possibilty that individuals have been taken by fishing operations cannot be excluded. However, the known population of Gray's Beaked whales generally resides outside of most commercial fishing operations and the impact of these operations is probably limited. (Klinowska and Cooke, 1991)
Threats and Conservation Status
The IUCN Red List note:
This species may not be as rare as some other species of the genus Mesoplodon, based on the number of records. In particular, they seem to be fairly common around New Zealand based on the frequency of strandings (Baker 1999). However, there are no estimates of abundance. There is no information on trends in the global abundance of this species.
Direct hunting has never been associated with this species. Pervasive gillnet and longline fisheries throughout the species' range raises concern that some bycatch is likely. Even low levels of bycatch might cause unsustainable impacts on this group of naturally rare cetaceans.
This species, like other beaked whales, is likely to be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration (Cox et al. 2006).
As a cold water species, Gray’s beaked whale may be vulnerable to the effects of climate change as ocean warming may result in a shift or contraction of the species range as it tracks the occurrence of its preferred water temperatures (Learmonth et al. 2006). The effect of such changes in range size or position on this species is unknown.
Evidence from stranded individuals of several similar species indicates that they have swallowed discarded plastic items, which may eventually lead to death (e.g. Scott et al. 2001); this species may also be at risk.
Gray's Beaked whales is protected by the Marine Mammal Protection Act of 1972. These laws are a strict guideline protecting marine mammals and their habitats. For M. grayi in particular, there is not enough information to determine its appropriate conservation status. Original sightings were so rare that the animals were thought to be close to extinction, but the increasing number of reliable sightings suggests there is a larger, more stable population than earlier believed. (Klinowska and Cooke, 1991)
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