According to the research, the levels of mercury found in Arctic foxes depend on their diets Scientists say that foxes in Arctic regions who feed on ocean prey are being exposed to dangerous levels of mercury. On one Russian island where the population of foxes has crashed, the researchers believe the toxin has played a key role in the decline. They say the findings could have important implications for conservation. The data is published in the Journal, PLOS ONE. Mercury levels in the world's oceans have doubled over the past 100 years, according to the UN, with more mercury deposited in the Arctic than on any other part of the planet. The Arctic Council says there has been a ten-fold increase in the levels of mercury found in top predators in the region over the past 150 years. Hair of the dog Now a team of researchers says it has found significant levels of mercury in different populations of Arctic foxes in different environments. On the small Russian island of Mednyi, part of the Commander Islands chain in the North Pacific Ocean, the foxes survive almost exclusively on sea birds with some also eating seal carcasses. The island's fox population declined mysteriously in the 1970s, and while the population is currently stable many of them are in poor condition, and have low body weight. They are listed as a critically endangered species with IUCN. Scientists at one time believed their shrinking numbers were caused by an infection, but they couldn't find the underlying cause.

Bear (Polar)

Polar bear: Ursus maritimus

Distribution: northern polar regions occurring in 5 nations - Greenland, Norway, Canada, United States, the former Soviet Union and also on Arctic sea pack ice usually within 300km of land. Some individuals wander up to 200km inland.

Population: 20,000 - 25,000 with 60% living in Canada. Status: vulnerable species (IUCN).

Habitat: favourite habitat is a combination of pack ice, open water and coastal land.

Description: coat colour varies from pure white to shades of yellow. Small ears; black eyes and nose.

Height: 1.6m to shoulder

Length: 2.2 - 2.5m.

Size of feet: 30cm long, 25cm wide.