The northern Dutch city Leeuwarden (in the province Friesland) has an otter park called Otterpark Aqualutra. The special animal can be examined from close range here. The partly educational centre tells you that otters are the ambassadors of fresh water environments: if otters are leaving a certain region in masses, it shows that the fresh water has been polluted in any way.

The address in case you happen to be in the neighbourhood: Otterpark Aqualutra, De Groene Ster 2, Leeuwarden. Its website at http://www.aqualutra.nl is only in Dutch but packed with photo's of otters and similar animals.

Otter is a problem solver computer system (also described as an automated deduction system), suited to solving logical and algebraic problems. A description from the Otter website:

"Our current automated deduction system Otter is designed to prove theorems stated in first-order logic with equality. Otter's inference rules are based on resolution and paramodulation, and it includes facilities for term rewriting, term orderings, Knuth-Bendix completion, weighting, and strategies for directing and restricting searches for proofs...Currently, the main application of Otter is research in abstract algebra and formal logic. Otter and its predecessors have been used to answer many open questions in the areas of finite semigroups, ternary Boolean algebra, logic calculi, combinatory logic, group theory, lattice theory, and algebraic geometry."

It works by taking a list of axioms and a hypothesis; Otter then works to try and find a pair of axioms, or an axiom and hypothesis which are mutually exclusive, by using logical steps. Otter then spits out a proof which effectively shows that one of the two statements in your input is wrong.

Otter has a good few predecessors from the sixties and seventies. It and its current relatives EQP and MACE have discovered a few interesting new results, such as proof of the Robbins conjecture. The latest versions of Otter are available to download from the Otter website, and come packaged with MACE.

Small carnivorous aquatic mammals. Members of the weasel family, mustilidae, along with ferrets, badgers and wolverines. Otters are the only aquatic weasels and do not venture far from water.

Otters exist throughout the world, except for the northern- and southernmost reaches and some of the South Pacific. Most species are diurnal and many are social and gregarious with others of their kind.

Most otters are brown or grey, they have a sleek, hydrodynamic shape. Most species have lighter fur on the underparts of their bodies, some are without any distinct markings. Like most other weasels, they scent mark with musk from anal glands and also with feces, to establish territory and find mates.

Most otters have webbed paws for better swimming. They are adapted to aquatic life with water-resistant fur, small ears and slitted nostrils that can be closed when submerged. Otters have sensitive whiskers which they use to detect water turbulence and find prey.

The diet of most otters consists entirely of small animals found in or very near water. They feed on frogs, eels, small birds, small fishes and shellfish. Many otters use their clawed forepaws to catch prey, although some catch prey in their teeth. Many species are very vocal and have specific vocalizations, easily recognized and seemingly adapted to very specific purposes.

TAXONOMY
Domain Eucarya
Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata
Superclass Gnathostomata
Class Mammalia
Infraclass Eutheria
Order Carnivora
Suborder Canoidea
Family Mustilidae
Subfamily Lutrinae

13 species in six genera. A fourteenth species is presumed extinct (see Threats to Otters, below). Much work has been done on the taxonomy of these animals in the last twenty years, and there is some disagreement over the exact delineations between genera, species and subspecies.

Genus Lontra (4 Species)
North American River Otter / Canadian Otter Lontra canadensis–is found across United States and Canada except for the Southwest and northernmost reaches of Canada. These animals are very dark brown to black with lighter coloration underneath and highly webbed feet. They catch prey in their mouths. About 20 subspecies

Marine Otter Lontra felina–native to a long band along the west coast of South America. They are the only exclusively marine otters of genus Lontra, although they will venture into freshwater streams. These animals are also the smallest of their genus and largely solitary animals. Marine otters live near rocky beaches and crags where they dwell in tunnels and caves. They are dark brown above with well-webbed paws and small ears set low on their head. Marine otters are hunted by orcas and sharks and sometimes by humans

Chilean River Otter / Southern River Otter Lontra provocax–inhabit calm marine and fresh water in Chile and Argentina. They are thick-coated, chocolate brown with a light underbelly and well-webbed paws. These animals are usually quite solitary.

Neotropical Otter Lontra longicaudis–habitat describes a NW to SE slash from NW Mexico to the Brazilian coast. These animals are similar in looks to the North American River Otter but smaller. They are brown to reddish with lighter underparts. They possess well-webbed paws. Neotropical otters are solitary and usually diurnal.

Genus Aonyx (2 species)
Cape Clawless Otter / African Clawless Otter Aonyx capensis–native to parts of sub-Saharan Africa, this otter has strong, unwebbed forepaws with great dexterity. Thick, silky fur, deep brown with much lighter underparts and often a white patch on the throat.

Congo Clawless Otter Aonyx congicus–found in a small area of central western Africa. Dark upper body with white beneath. Three subspecies.

Genus Enhydra (1 species)
Sea Otter Enhydra lutris–dark brown with lighter head and face. They live in a narrow band along the coast of China, across the Bering Strait and south as far as Baja California. The sea otter rarely sets paw on dry land. One of the two largest mustalids, the sea otter can grow as large as 100 pounds. Their diet is largely made up of mollusks, fish and sea urchins. This creature was hunted almost to extinction in the Nineteenth Century for its pelt.

Genus Amblonyx (1 species)
Asian Clawless Otter / Oriental Short Clawed Otter Amblonyx cinereus–the smallest of all otters, this animal is seldom bigger than 35 in (90 cm). They are short, stout little creatures with deep brown fur and a lighter patch on the throat and cheeks. Despite the name, the Asian clawless otter is not clawless, but has small, blunt claws. This species possesses only slight webbing on the paws. Their range is through central Asia.

Genus Lutra (3? species)
Eurasian River Otter / European River Otter Lutra lutra–has the largest range of any otter, this species is found across all of Europe, Asia and down south as far as Java. It lives in coastal and freshwater areas. Eurasian river otters are dark colored with light fur beneath their body and a thick, wooly undercoat. They are medium-sized, as otters go, with maximum body weight at around 26 pounds (12 kg) and lengths up to 38 inches (95 cm).

Hairy Nosed Otter Lutra sumatrana–has a small range in Thailand and Cambodia south to Indonesia. These animals have a deep reddish or brownish coat with a white patch on the throat and/or around the mouth. This is an extremely rare and poorly-studied species.

Spotted-Necked Otter / African River Otter Lutra maculicollis–found in most of the freshwater lakes, streams and river systems south of the Sahara Desert (although they are not found in that arid southwest corner of the continent). These very small otters (up to 13 pounds) are very dark with some white spotting on the neck and foreparts. They possess a thick, strong tail and well-webbed paws.

Genus Lutrogale (1 species)
Indian Smooth-Coated Otter / Asian River Otter Lutrogale perspicillata–lives in marshes and along coastlines throughout India and Southeast Asia, south to Indonesia. This is the largest of the Asian otter species, with weights up to 24 pounds. The coat of this species is smooth and short, as the name implies. They possess a thick, long tail that is slightly flattened at the tip. This otter is sometimes included in genus Lutra.

Genus Pteronura (1 species)
Giant Otter Pteronura brasiliensis–ranges through Brazil, Colombia and central South America in river systems which include the Orinoco, Amazon and La Plata and their tributaries. These otters are typically dark brown with very well-webbed feet. These big animals can grow to over 5 feet long and as heavy as 66 lbs. The giant otter is endangered because of being depleted by pelt hunters.

TOOL-USING WEASELS
Sea otters use rocks to bash open the shells of mollusks. The otter floats on its back and pounds the shellfish on a stone, thus cracking open the shell. Apart from primates, otters are one of the very few animals to use tools, a fact which has caused some slight consternation among certain animal behaviourists.

THREATS TO OTTERS
Most species of otters are threatened and some are endangered. Habitat loss has taken a big toll on these animals, as they favour areas near bodies of water, and these are prime real estate.

A subspecies called Maxwell's Otter (Lutrogale perspicillata maxwelli) was native to Iraq, living in the salt marshes of the Euphrates River. Due to large-scale draining of their habitats, the Maxwell's otter died off in large numbers and is now presumed extinct.

Pollution and hunting have also threatened to wipe out many species of otters. Otters are especially vulnerable to oil spills and industrial waste. They have also been hunted as pests in certain places as they compete with fishermen for fish. As noted above, some species are a favourite food of sharks, killer whales and other sea-going meat-eaters. This too, may deplete their numbers.

References: Lioncrusher's Domain online - http://www.lioncrusher.com/Lutrinae.htm
Bateman, Graham, ed., "All the World's Animals; Carnivores" (Equinox, Oxford, 1984).
Otternet.com

Ot"ter (?), n. [OE. oter, AS. Otor; akin to D. & G. otter, Icel. otr, Dan. odder, Sw. utter, Lith. udra, Russ, vuidra, Gr. water serpent, hydra, Skr. udra otter, and also to E. water. 137, 215. See Water, and cf. Hydra.]

1. Zool.

Any carnivorous animal of the genus Lutra, and related genera. Several species are described. They have large, flattish heads, short ears, and webbed toes. They are aquatic, and feed on fish. Their fur is soft and valuable. The common otter of Europe is Lutra vulgaris; the American otter is L. Canadensis; other species inhabit South America and Asia.

2. Zool.

The larva of the ghost moth. It is very injurious to hop vines.

Otter hound, Otter dog Zool., a small breed of hounds, used in England for hunting otters. -- Otter sheep. See Ancon sheep, under Ancon. -- Otter shell Zool., very large bivalve mollusk (Schizothaerus Nuttallii) found on the northwest coast of America. It is excellent food, and is extensively used by the Indians. -- Sea otter. Zool. See in the Vocabulary.

Ot"ter, n.

A corruption of Annotto.