Cuvier's beaked whale

History of discovery

The French anatomist Georges Cuvier, in his treatise Sur les Ossements fossiles (1823), first described the species based on an imperfect skull from the Mediterranean coast of France. It had been obtained by M. Raymond Gorsse in the department of Bouches-du-Rhône, near Fos, in 1804 from a local who had found it on the seashore the previous year. Cuvier named it Ziphius cavirostris, the specific name being derived from the Latin cavus for "hollow" or "concave", in reference to the deep hollow (the prenarial basin) in the skull, a diagnostic trait of the species. Cuvier believed it to represent the remains of an extinct species. Zoologists did not realize the extant nature of the species until 1850, when Paul Gervais compared the type specimen to another that had stranded itself at Aresquiès, Hérault, in May of the same year, and found the two to be identical. There is no connection between Cuvier's beaked whale and the mythical Ziphius, or "Water-Owl", a creature in medieval folklore which had the characteristics of both an owl and a fish. Its dorsal fin was said to be sword-shaped, and pierced ship's hulls, while the beak was said to resemble an owl's head.

Description

The body of Cuvier's beaked whale is robust and cigar-shaped, similar to those of other beaked whales, and can be difficult to distinguish from many of the mesoplodont whales at sea. It grows to about 5–7 m (16–23 ft) in length and weighs 2,500 kg (5,500 lb). No significant size difference is seen between sexes.

Its dorsal fin is curved, small, and located two-thirds of the body length behind the head. Its flippers are equally small and narrow and can be tucked into pockets in the body wall, presumably to prevent drag while swimming. Like other beaked whales, its flukes are large and lack the medial notch found in all other cetaceans. The head is short with a small, poorly defined rostrum and a gently sloping melon. A pair of throat grooves allows the whale to expand this region when sucking in its prey.

Cuvier's beaked whale has a short beak in comparison with other species in its family, with a slightly bulbous melon, which is white or creamy in color, and a white strip runs back to the dorsal fin about two-thirds of the way along the back. The rest of the body color varies by individual: some are dark grey; others are a reddish brown. Individuals commonly have white scars and patches caused by cookiecutter sharks. The dorsal fin varies in shape from triangular to highly falcate, whilst the fluke is about one-quarter the body length. They live for around 40 years.

Diving adaptations

Food and foraging

Cuvier's beaked whales feed on several species of squid, including those in the families Cranchiidae, Onychoteuthidae, Brachioteuthidae, Enoploteuthidae, Octopoteuthidae, and Histioteuthidae; they also prey on deep-sea fish. In 2014, scientists reported that they had used satellite-linked tags to track Cuvier's beaked whales off the coast of California, and found the animals dived up to 2,992 m (9,816 feet) below the ocean surface and spent up to two hours and 17 and a half minutes underwater before resurfacing, which represent both the deepest and the longest dives ever documented for any mammal.

Range and habitat

Cuvier's has a cosmopolitan distribution in deep, offshore waters from the tropics to the cool, temperate seas. In the North Pacific, it occurs as far north as the Aleutians and in the North Atlantic as far north as Atlantic Canada in the west to Shetland in the east. In the Southern Hemisphere, it occurs as far south as Tierra del Fuego, South Africa, southern Australia, New Zealand, and the Chatham Islands. It also frequents such inland bodies of waters as the Gulfs of Mexico and likely the Caribbean and Mediterranean Seas. Mediterranean population is genetically distinct from North Atlantic population(s).

Cuvier's beaked whale may be one of the most common and abundant of the beaked whales, with a worldwide population likely well over 100,000. An estimated 80,000 are in the eastern tropical Pacific, nearly 1,900 are off the west coast of the United States (excluding Alaska), and more than 15,000 are off Hawaii.

In 2011, a tagged Cuvier's beaked whale dove to 2,992 m, (9,816 ft) which is the deepest recorded dive by any mammal. The whales' rib cages can fold down so as to reduce air pockets and decrease buoyancy.

Conservation

Japanese whalers in the past opportunistically caught Cuvier's, taking between three and 35 each year (before 1955). The species has been reported taken incidentally in fisheries in Colombia, the Italian swordfish fishery, and in the drift gillnet fishery off the U.S. west coast, where between 22 and 44 individuals died each year off California and Oregon from 1992 to 1995. Cuvier's beaked whale is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS) and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS). The species is further included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU) and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).

Beaked whales may also be sensitive to noise: a higher incidence of strandings has been recorded in noisy seas such as the Mediterranean, and multiple mass strandings have occurred following operations by the Spanish Navy in the Canary Islands. In 2019, a review of evidence on the mass strandings of beaked whale linked to naval exercises where sonar was used was published. It concluded that the effects of mid-frequency active sonar are strongest on Cuvier's beaked whales but vary among individuals or populations, and the strength of the whales' response may depend on whether the individuals had prior exposure to sonar. The report considered that the most plausible explanation of the symptoms of decompression sickness such as gas embolism found in stranded whales to be the whales' response to sonar. It noted that no more mass strandings had occurred in the Canary Islands once naval exercises where sonar was used were banned there, and recommended that the ban be extended to other areas such as the Mediterranean where mass strandings continue to occur.

Taxonomy

Its nearest relative, the only other living member of the subfamily Ziphiinae, is Shepherd's beaked whale (Tasmacetus sheperdi).