Shepherd's beaked whale (Tasmacetus shepherdi), also commonly called Tasman's beaked whale or simply the Tasman whale, is a cetacean of the family Ziphiidae and the only species in the genus Tasmacetus. The whale has not been studied extensively. Only four confirmed at sea sightings have been made and 42 strandings recorded (as of 2006).<!-- DO NOT CHANGE (see Talk page) --> It was first known to science in 1937, being named by W. R. B. Oliver after George Shepherd, curator of the Wanganui Museum, who collected the type specimen near Ohawe on the south Taranaki coast of New Zealand's North Island, in 1933.

Description

center|thumb|Illustration depicting the morphology and coloration of a typical adult.

Adults can reach lengths of to and weigh about 2.32 to 3.48 tons. At birth they may be about long. The longest recorded lengths were for a male and for a female.

They are robust and large-bodied for beaked whales, having a bluff melon and a long, dolphin-like beak.

It is the only species of ziphiid with a full set of functional teeth (17 to 27 pairs in both the upper and lower jaws).

Population and distribution

Sightings and stranding records indicate that the species has a circumpolar distribution in southern hemisphere. No population estimates exist for Shepherd's beaked whale. As of 2006, there have been about 42 stranding records of the species from New Zealand (including the Chatham Islands, 24), Argentina (7), Tristan da Cunha (6), Australia (3), and the Juan Fernández Islands (2). The northernmost record was at Shark Bay in Western Australia in 2008. There have been five unconfirmed sightings (mostly from New Zealand), as well as a "probable" sighting near Shag Rocks and four confirmed sightings—the first two confirmed sightings occurred in 1985, within a few minutes of each other, off the Tristan da Cunha group (first sighting at ); the third in 2002 near Gough Island (); and the fourth in 2004 south of Tasmania (). In January 2012, a group of up to a dozen of this species were photographed and filmed by the Australian Antarctic Division south of Portland, Victoria.

Multiple sightings of the species have been reported from Otago submarine canyons off Otago coast, New Zealand. Sightings have been recorded throughout the year with vocalization recordings, suggesting regular presences there. followed by four sightings in 2017, one or more sighting(s) in 2018, one sighting in 2019, four or five sightings in 2021, five sightings in 2022 including a pod of 15-20 animals.

There have been additional sightings from other parts of New Zealand, such as off Gisborne, several sightings off Kaikōura, off Fiordland, Taranaki, and so on. The species is seldom seen because of its deep, offshore distribution in waters where sighting conditions can be difficult (the "Roaring Forties" and "Furious Fifties").

thumb|Dorsal fin region of a male showing extensive scarring, likely caused by aggression with other males.|left

Food and foraging

Like other beaked whales, Shepherd’s beaked whales possess a pair of V-shaped throat grooves that are thought to facilitate suction feeding by creating negative pressure within the mouth as the tongue retracts and the throat grooves expand, powerfully drawing prey inward like a biological vacuum. They are presumed to use echolocation to locate prey and may also use vision at close range, particularly when targeting bioluminescent species. However, their unusual full set of functional teeth may also be advantageous in capturing fish, which constitute a substantial portion of their diet.

Shepherd's beaked whales appear to have a very diverse diet composed of both fish and squid, rather than feeding primarily on squid like many other beaked whales. Analyses of stomach contents revealed cephalopod taxa such as Histioteuthis atlantica, Stigmatoteuthis dofleini, Todarodes filippovae, Ancistrocheirus lesueurii, Taningia danae, Octopoteuthis sp., Teuthowenia pellucida, Ommastrephes bartramii, Pholidoteuthis sp., Lycoteuthis lorigera, Mastigoteuthis sp., and Brachioteuthis picta; recorded fish taxa include Argentine hake, serranids, Brotula sp., orange roughy, splendid alfonsino, mirrorbelly, eelpout, grenadiers, monkfish, Neobythites, and lanternfish (Symbolophorus sp., Diaphus sp.). Other prey, such as crabs (Peltarion spinulosum), have been recorded.

The species may vary its foraging strategy spatially or temporally in response to prey movements and habitat use. Several prey species, including splendid alfonsino and squid such as Stigmatoteuthis dofleini and Taningia danae undergo diel vertical migrations, occupying deeper waters during the day and rising toward shallower depths at night. This may indicate that the whales shift between slope, seamount, and more oceanic habitats to exploit prey concentrations at different depths and times.thumb|left|First underwater sighting of live Shepherd's beaked whales, near [[Inaccessible Island, Tristan da Cunha, January 2017.]]

Vocal behavior

A recent study found Shepherd's beaked whale to produce a variety of ultrasonic pulses used in echolocation. Like other beaked whales, these high-frequency clicks are thought to assist in navigation and prey detection during deep dives, and the frequency-modulated upsweep pulses may be unique to this species.

Predators

thumb|A stranded adult male photographed in New Zealand bearing numerous cookiecuttershark wounds, most concentrated on the ventral surface, especially around the genital area.

Killer whales and large sharks may prey on Shepherd's beaked whales. There have also been unconfirmed reports of kleptoparasitic interactions with killer whales. Plastic debris and longline hooks have been found in the stomachs and intestines of some individuals, which could lead to internal trauma or starvation if the material blocks their digestive tracts.

The species was featured on a 45p commemorative stamp issued by Tristan da Cunha in 2019 as part of a set celebrating different species of whale.

See also

  • List of cetaceans

References

Sources

  1. Shepherd's beaked whale in the Encyclopedia of Marine Mammals Thomas A. Jefferson, 1998.
  2. Whales, Dolphins and Porpoises Carwardine, 1995.