Andrew's beaked whale (scientific name: Mesoplodon bowdoini) 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. They are marine mammals within the order of cetaceans.
There have been very few sightings of this whale due to its spending little time on the surface. As of 2001, this whale was known from 35 specimens, all from strandings; of which 21 were from New Zealand and its surrounding islands. Most of the rest were from southern Australia.
|Andrew's beaked whale. Source: FAO|
|Size comparison of an average human against Andrew's beaked whale. Source: Chris Huh|
General physical features: endothermic metabolism; homoiothermic; and bilateral symmetry. Of the roughly 35 specimens studied, the following are specific to Andrew's beaked whale:
- individuals weigh 2.6 tons at their maximum and at birth the average length is approximately two meters (m).
- Females grow to an average of 4.6 m., with males growing slightly longer to 4.8 m, illustrating the sexual dimorphism
- The colour of males ranges from dark grayish-blue to black, except for the beak, the tip of the rostrum and lower jaw, which are white in color.
- Females have more of an off-white beak. (Baker, 2001; Jefferson, Leatherwood, and Webber, 1993; Reeves et al., 2002)
Andrew's whale females or young are distinguished from other Mesoplodon species by their heads, which have a small melon and as a result, slants down dramatically from the body. Also, females and young have short, thick beaks. The dorsal fin of this species is rather small for its body size. This fin is found in the middle of the back, and it is triangular and blunt tipped. (Reeves et al., 2002)
The teeth of males are helpful in identification. Males have two teeth located in the lower jaw within a set of sockets in the middle of the beak. Females also contain these teeth, but they are not visible since they do not erupt through to the surface. (Baker, 2001; Culik, 2003)
Key general behaviours are: natatorial; motile; and solitary. Relatively little is known about the behaviour of the Andrews' beaked whale, which is generally viewed as a. slow, sluggish marine mammal.
Beaked whales have flipper pockets, which allow the flippers to be tucked away to reduce drag when swimming. Andrew's beaked whale spends little time at the water surface, making individuals more difficult to identify or find. When spotted, these whales are generally alone, and if in a group, it is typically accompanied by no mroe than six others. (Jefferson, Leatherwood, and Webber, 1993; Reeves et al., 2002)
Key reproductive features are seasonal breeding; gonochoric/gonochoristic/dioecious (sexes separate); viviparous. Due to the lack of scarring on Andrew's beaked whales (common with many other beaked whales), investigators believe that there is no physical competition for partners.
Little is known about the mating system of this species. ("The Toothed Whales", 1975) The scarce information on the reproductive system of Andrew's beaked whale is from occasional observations of young. The calving season occurs during the summer and autumn. (Reeves et al., 2002)
Distribution and Movements
Mesoplodon bowdoini, also known as Andrew's beaked whales, can be found in cool temperate water such as the Indo-Pacific Ocean. The waters around New Zealand and off the southern coast of Australia are home to this whale. ("The Toothed Whales", 1975)
This beaked whale inhabits temperate Southern Hemisphere waters at the southern end of the continental land masses. They may be found in both pelagic and coastal environments. These animals prefer to forage at depths below the 1000 metre line. This is possibly due to the distribution of squid and other food sources not yet identified. The great depths to which these marine mammals travel can result in dives that last longer then 45 minutes. (Jefferson, Leatherwood, and Webber, 1993)
Andrew's beaked whale feeds in deep waters, primarily on Cephalopoda. When squid are not available, Actinopterygii become a secondary source of food. (Jefferson, Leatherwood, and Webber, 1993) Andrew's beaked whale affects the trophic chain by feeding on squid and occasionally fish and mollusk populations. No relationships with other marine animals are known. ("The Toothed Whales", 1975)
Threats and Conservation Status
Andrew's beaked whale is protected under the 1972 Marine Mammal Protection Act (MMPA). This established an end to the hunting, harassing, capture or killing of marine mammals in US waters and by US citizens. MMPA also extended the ban on the importation of marine mammals or their products into the country. (U.S. Department of the Interior, 2003)
The IUCN Red List reports:
There have been no confirmed sightings at sea, and no population genetic analyses have been done. As such, nothing is known of the population status of Andrews' beaked whale.
No threats are known (Reeves et al. 2003), but there are a number of potential threats.
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).
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.
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.
Predicted impacts of global climate change on the marine environment may affect this species of whale, although the nature of impacts is unclear (Learmonth et al. 2006).
IUCN Red List classifies this Data Deficient, while the U.S. Federal List and CITES confer special status.
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