True's Beaked Whale

Classification

Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Ziphiidae
Genus: Mesoplodon
Species: mirus
Common Names: True's beaked whale
Irish Name: An míol mór socach breá
 

Key Identification Features

Max. adult body length/weight: 6m / 1,500kg
Average adult body length/weight:5m / 1,300kg
Average length/weight of calf at birth:2m / 136kg
Blow: Barely visible.
Head: Relatively small head with a bulging forehead. A depression is found in the top of the head behind the blowhole.
Dorsal Fin: The dorsal fin is small and slightly sickle-shaped. It is situated roughly two-thirds of the way along the body.
Colouration: Blue to dark grey upper body, with lighter patches on the underside and throat. The colour may vary to an overall grey or brownish colour.
Markings: Some stranded animals have been reported with yellow, purple, hazel or sienna spots on the lower flanks. Adult males have white rake marks (made by the teeth of other males) on the sides and back. There is a dark patch around the eye.
 

Field Identification

Without a good view of the head, they are extremely difficult to identify at sea. Their tail flukes are generally not visible even when the animal is diving. They are shy of shipping and boats. The single animal photographed alive in European waters was identified through its characteristic teeth. The lower jaw is slightly protruding with two teeth visible near the tip of the lower jaw in adult males. They have a medium sized beak.
 

Species Similar in Appearance

Other Mesoplodon species.
 

Behaviour

These animals are shy of shipping and dive quickly if disturbed. Adults have been seen breaching a number of times in the waters of the Bay of Biscay in 2001 and it is thought that breaching is not uncommon for this species, with one animal breaching 17 times in succession.
 

Status and Distribution

Little is known of the population size of this species. What little we do know has been gleaned from a handful of sightings and about 40 stranded specimens.

It is thought that True's beaked whales occupy all oceans outside of the polar seas. Stranded animals have been discovered on the east coast of Canada and the USA, on the Irish west coast and Bay of Biscay, the North African Coast and the South coast of Australia and South Africa. The northern hemisphere population may be a distinct from their southern hemisphere counterparts, as the southern hemisphere animals have slight cranial and pigmentation differences.

Prior to 2001 no True's beaked whale had ever been photographed and definitely identified alive in North European Waters, even though the North Atlantic is thought to represent their centre of population. In summer 2001 and adult male was photographed breaching by observers on the P&O vessel, the Pride of Bilbao, whilst travelling along the shelf edge in the Bay of Biscay. This is the most recent of 3 suspected sightings of True's beaked whale in the Bay of Biscay.
 

Where and When Best Seen in Ireland

Although Ireland has had a number of strandings, it is possible that these drifted dead on the Gulf Stream from mid-Atlantic waters. Seven of the ten strandings in Northern Europe occurred on the Irish West Coast and these animals are probably relatively common in deep water canyons beyond the shelf edge off our west coast.
 

Food and Feeding

The main food of the True's beaked whale is squid and some deep- water fish species
 

Reproduction and Life Cycle

Max. life expectancy: Unknown.
Average life expectancy: Unknown.
Mating Occurs: Unknown.
Season of birth: Spring.
Gestation: Unknown.
 

Social Structure

Little or nothing is known of their social structure. Two females and a calf were seen together in Southern California.
 

Conservation Issues

Not enough is known about these animals to determine their main threats, although new trends in deep water trawling may pose some difficulties, as they rely on deep-water canyons as their primary habitat.
 

Stranded Animals

The flippers are placed well forward and low down on the animal. There is a pronounced ridge on top of the tail-stock. As with other “beaked whales” their flukes have no notch. Males have two small teeth that protrude from a point around 5cm from the tip of the lower jaw. In females, these teeth do not erupt but may be found in a vestigial below the gum. The flippers fold into recesses in the body wall.
 

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