Otters
Otters are one of the smallest marine mammals with a thick, waterproof and insulating layer of fur.
Unfortunately it was this fur that first attracted hunters and led to the virtual extinction of several
species at the beginning of this century. The sea otter Enhydra lutris is the largest species and its
ability to use tools, such as stones from the seabed, to break open clams is a behavioural characteristic
few other animals have. They used to range from Japan, across the Alaska Peninsula and down to
California but after being severely hunted it is now confined to smaller isolated populations in
southeast Alaska, British Columbia, Washington and California. Numbers increased steadily until the
1970s when they nose-dived and sea otters were put on the endangered species list. Conflict exists
between them and fishermen and the threats from pollution and disease are increasing. In Alaska the
sea otters are being heavily predated by killer whales forced to find new sources of food by the low
numbers of their usual diet, steller sea lions and harbour seals.
South America has several species of otter; the South American river otter Lontra longicaudis has the
widest distribution, from Mexico to northern Argentina. In some countries it is still classed as
vulnerable to extinction but most countries have no reliable data on population size. The Southern
river otter Lontra provocax is restricted in distribution to southern Chile and western Argentina. The
marine otter Lontra felina occurs from Peru southwards to the tip of South America. These two species
have been severely depleted by hunting and their actual population sizes are uncertain but both have
been classed as endangered. The major threats currently affecting all three species are habitat
destruction and water pollution.
The common otter Lutra lutra has the widest distribution, ranging from Ireland in the west to Japan in
the east and from the arctic to North Africa and Sri Lanka. This species of otter is vulnerable to
extinction because there has been a severe loss of available habitat as well as increasing levels of
pollution throughout its range.
Three species of otter exist in sub-Saharan Africa, the small-toothed clawless otter Aonyx congicus
being the only one that has been listed as near threatened. No data exists as to the current population
levels but they are still being hunted and their habitat denuded.
The hairy-nosed otter Lutra sumatrana was classed as vulnerable to extinction in 1996 but in the 2000
edition of the redlist there was insufficient data for population levels to be assessed. The threats to this
species are not well documented but habitat destruction and depletion of prey species could be
contributing to its decline. The Giant otter Pteronura brasiliensis has become endangered in the last
four years due to multiple anthropogenic influences arising from increased colonisation of tropical
lowland rainforests. Destruction of forests leading to soil erosion, illegal hunting, over-fishing of prey
species are only a few of the problems facing this species.
Even with our increasing scientific knowledge the problems of monitoring population trends becomes
apparent with several species of otter previously threatened by extinction to various degrees but now
there is insufficient information to say how many may exist today. Of those species we have sufficient
data on the otter group shows the greatest number that have recently changed their threatened status for
the worst.