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Otter

Encyclopedia : O : OT : OTT : Otter

The aquatic (sometimes marine) carnivorous mammals known as otters form part of the large and diverse family Mustelidae, which also includes weasels, polecats, badgers, and others. With 13 species in 7 genera, otters have an almost worldwide distribution.

English-speakers may use the collective noun romp to refer to a group of otters (a Google search as of 29 May 2006 lists 63 occurrences of the phrase "romp of otters", but the OED does not appear to record this usage).

Contents

Physical characteristics

Otters have a dense layer (1,000 hairs/mm², 650,000 hairs per sq. in) of very soft underfur which, protected by their outer layer of long guard hairs, keeps them dry under water and traps a layer of air to keep them warm.

All otters have long, slim, streamlined bodies of extraordinary grace and flexibility, and short limbs; in most cases they have webbed paws. Most have sharp claws to grasp prey, but the short-clawed otter of southern Asia has only vestigial claws, and two closely-related species of African otter have no claws at all: these species live in the often muddy rivers of Africa and Asia and locate their prey by touch.

Diet

Most otters have fish as the primary item in their diet, supplemented by frogs, crayfish and crabs; some have become expert at opening shellfish, and others will take any available small mammals or birds. To survive in the cold waters where many otters live, they do not depend on their specialised fur alone: they have very high metabolic rates and burn up energy at a profligate pace: Eurasian otters, for example, must eat 15% of their body-weight a day; sea otters, 20 to 25%, depending on the temperature. This prey-dependence leaves otters very vulnerable to prey depletion. In water as warm as 10°C an otter needs to catch 100 g of fish per hour: less than that and it cannot survive. Most species hunt for 3 to 5 hours a day, nursing mothers up to 8 hours a day.

Species

Northern River Otter

The northern river otter (Lontra canadensis) became one of the major animals hunted and trapped for fur in North America after European contact. As one of the most playful and active species of otter, they have become a popular exhibit in zoos and aquaria, but unwelcome on agricultural land because they alter river banks for access, sliding, and defense. River otters eat a variety of fish and shellfish, as well as small land mammals and birds. They grow to 1 m (3 to 4 feet) in length and weigh from 5 to 15 kg (10 to 30 pounds). Once found all over North America, they have become rare or extinct in most places, although flourishing in some locations.

Some jurisdictions have made otters a protected species in some areas, and some places have otter sanctuaries. These sanctuaries help ill and injured otters to recover.

Sea Otter

Sea otters (Enhydra lutris) live along the Pacific coast of North America. Their historic range included shallow waters of the Bering Strait and Kamchatka, and as far south as Japan. Sea otters have some 200,000 hairs per square cm of skin, a rich fur for which humans hunted them almost to extinction. By the time the 1911 Fur Seal Treaty gave them protection, so few sea otters remained that the fur trade had become unprofitable.

Sea otters eat shellfish and other invertebrates (especially clams, abalone, and sea urchins ), and one can frequently observe them using rocks as crude tools to smash open shells. They grow to 1 to 2 m (2.5 to 6 feet) in length and weigh 30 kg (25 to 60 pounds). Although once near extinction, they have begun to spread again, starting from the California coast.

Unlike most marine mammals (seals, for example, or whales), sea otters do not have a layer of insulating blubber. As with other species of otter, they rely on air-pockets trapped in their fur.

Maxwell's Otter

Zoologists believe that a sub-species of otter Lutrogale perspicillata maxwelli (named 'Maxwell's Otter' after the British naturalist Gavin Maxwell and the subject of his book Ring of Bright Water) lived in the Tigris-Euphrates alluvial salt marsh of Iraq. Some have suggested that this sub-species may have become extinct as a result of the large-scale drainage that has taken place in the region since the 1960s.

European Otter

Otters also inhabit in Europe. In the United Kingdom they occurred commonly as recently as the 1950s, but have now become rare due to the former use of chlorinated hydrocarbon pesticides and as a result of habitat-loss. Numbers reached a low point in the 1980s, but with the aid of a number of initiatives, by 1999 estimated numbers indicated a recovery to just below 1,000 animals. The UK Biodiversity Action Plan envisages the re-introduction of otters by 2010 to all the UK rivers and coastal areas that they inhabited in 1960. Roadkill deaths have become one of the significant threats to the success of their re-introduction.

Otters in mythology

Norse mythology tells of the dwarf Ótr habitually taking the form of an otter. (Note that the Old Icelandic word otr means "otter"; these and cognate words in other Indo-European languages ultimately stem from a root which apparently also gave rise to the English words "water", "wet" and "winter".)

Otters in literature

Otters appear very commonly in Brian Jacques's Redwall series.

Note also:

List of species

Genus Lutra Genus Hydrictis Genus Lutrogale Genus Lontra Genus Pteronura Genus Aonyx Genus Amblonyx Genus Enhydra

External links

 

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