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Beaked whale

From Academic Kids

Beaked whales
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Subclass:Eutheria
Order:Cetacea
Suborder:Odontoceti
Family:Ziphiidae
Genera

Berardius
Hyperoodon
Indopacetus
Mesoplodon
Tasmacetus
Ziphius

A beaked whale is any of at least 20 species of small whale in the family Ziphiidae. They are one of the least-known families of large mammals: several species have only been described in the last two decades, and it is entirely possible that more remain as yet undiscovered. Six genera have been identified. Three of these, Indopacetus, the Hyperoodon and the Mesoplodon, are united in a single subfamily, the Hyperoodontidae.

The known beaked whales range in size from about 3.4 metres to almost 13 metres, and can weigh anywhere between 1 and 15 tonnes. They are found in all oceans and most species rarely venture into the relatively shallow water of the continental shelves. They are very difficult to identify in the wild: body form varies little from one species to another, and the observer must rely on often subtle differences in size, colour, shape of forehead, and length of beak.

The beaked whales are the second-largest family of Cetaceans (after the dolphins) and were one of the first groups to diverge from the ancestral lineage. The earliest known beaked whale fossils date to the Miocene, about 20 million years ago. They are creatures of the ocean deeps, feeding, so far as is known, on or near the sea floor. They have an extraordinary ability to dive for long periods—20 to 30 minutes is common, and 80 minute dives have been recorded—and to great depths: certainly 1000 metres and quite possibly more.

Beaked whales tend to associate in small family groups and avoid shallow water. Known areas where they congregate include the deep waters off the edge of continental shelves, and close to bottom features like seamounts, canyons, escarpments, and oceanic islands including the Azores and the Canaries. Diet is primarily deep water squid, but also fish and some crustaceans.

Because of their preferred habitat and their inclination to make very long dives, they are very difficult to observe, and little is known of most species. Several have yet to be formally described or named; others are known only from remains and have never been sighted alive. Only three or four of the 20-odd species are reasonably well-known. Baird's and Cuvier's Beaked Whales were subject to commercial exploitation off the coast of Japan; and the Northern Bottlenose Whale was extensively hunted in the northern part of the North Atlantic late in the 19th and early in the 20th centuries.

For many years, most of the beaked whale species were insulated from human impact because of their remote habitat. However there are now clear issues of concern: studies of stranded beaked whales show rising levels of toxic chemicals in their blubber (as a top-order predator they are, like raptors, particularly vulnerable to build-up of biocontaminants) and they frequently have ingested plastic bags (which do not break down and can be lethal). With the ongoing worldwide expansion of deepwater fisheries (particularly since the collapse of Atlantic Cod stocks late in the 20th century), beaked whales are more and more frequently trapped in trawl nets, and are also assumed to be vulnerable to prey depletion.

Four of the more than 20 beaked whale species are classified by the IUCN as "lower risk, conservation dependent": Arnoux's and Baird's Beaked Whales, and the Northern and Southern Bottlenose Whales. None of the remaining species are classified - not because they are considered secure, but because their status is simply unknown.

For further details on the genus Mesoplodon, containing thirteen of the beaked whales, see Mesoplodont Whale.

de:Schnabelwale sv:Näbbvalar pl:Wale dziobogłowe

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