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Why do polar foxes disappear?

October 11, 2002

The polar foxes inhabit the Commandor Islands. Due to isolation, the polar foxes of each island differ from the ones inhabiting the mainland and even from the neighbors populating other islands of the archipelago. As a matter of fact, each island is populated by an individual polar fox subspecies. Isolated populations have always been of interest for biologists, but in this particular case their interest to the polar foxes population quantity, health state and living conditions is not only of scientific nature - the Commandor Islands polar foxes has always been hunted for (as they are bigger than the continental ones). D.A. Ryazanov, researcher of the Kamchatkа Institute for Ecology and Nature Management, Far-East Branch, Russian Academy of Sciences, has studied the polar foxes of two neighboring islands - Bering Island and Medny (Copper) Island. Ryazanov has recently published the observations dating back to ten years, but there has been no fundamental change since that time. At present, the polar fox hunting is carried out only on Bering Island. As for Medny (Copper) Island, the polar fox authorized hunting ceased there in 1965. However, on that particular island these animals are now in distress.
      
Ryazanov investigated the islands in summertime when the polar fox cubs already got out of the burrows, but did not leave the litter yet, and in winter, during the hunting season. The animals were marked so that the researcher could track their travel along the island throughout the year. On Bering Island the researcher calculated 1000 to 1500 animals in various years. Based on this data, no judgments can be made as regards to the increase or reduction of the polar fox population quantity, these deviations can be accounted for by the ordinary quantity fluctuations. Anyway, the animals are so numerous on the island that it is getting a bit crowded. The polar foxes have to migrate in search of food. In summertime the polar foxes settle in the vicinity of the poultry-yards in the southern part of the island, near the salmon spawning places or the northern fur-seal breeding ground. As winter approaches the birds fly away, the rivers get frozen, and the coastline remains the only place where the polar foxes can find food. During this period they have to live on carrion of the marine mammals and birds which are most numerous on the northern and eastern coasts, and this is where the polar foxes move to. Despite the difficulties the animals face and the hunt for polar foxes, the life of this species is stable on Bering Island.

As for Medny (Copper) Island, the situation is sorrowful. In 1965 the island was inhabited by approximately 600 adult animals, and in 1978 the population accounted not more than 100-120. The primary reason the polar foxes` disappearance was the cubs` high death-rate from the ear disease caused by itch-mites. So, at that point the subspecies was registered in the Red Book as the one being on the verge of extinction.
      
According to Ryazanov`s estimates, the current quantity of adult animals on the island makes up about fifty. The density being so low, the animals do not have to compete with each other and migrate over the islad in search of food. They are so fastidious about food that they do not eat carrion. But regardless of the abundance, the polar foxes of Medny (Copper) Island do not practically reproduce themselves - their posterity is not numerous, the death-rate being high. Some couples produce no cubs at all. The researcher assumes that the polar foxes have become so scanty that even an insignificant growth of the adult animals death-rate may result in an irreplaceable loss. For retaining and restoring of the subspecies population, it is necessary, firstly, to set up a preserve on the island, and secondly, to sort out what is going on with the polar foxes. The itch-mite can hardly be considered the sole cause of the cubs` death, since this parasite has always existed on Medny (Copper) Island and it can also be found on Bering Island. Probably, hunting has played its role - for forty years the sires on the island have been artificially selected and fed up, thus upsetting the genetic balance inherent to a wild population. As s result, some of the Medny (Copper) Island polar foxes could have lost part of the gene pool, and therefore they have lost resistance to some diseases. That is why the scientists urgently need to study the genetic diversity of polar foxes of Medny (Copper) Island and the causes of their mortality, along with treating the animals from the mange. Ryazanov is confident that only a complex solution to the problem can become a cost-efficient investment and help to preserve the unique subspecies.

Informnauka (Informscience) Agency