Seals, Sea Lions and Walruses




Дата канвертавання24.04.2016
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Seals, Sea Lions and Walruses
Monk seals are one of the most threatened of the seal populations and indeed the Caribbean monk seal Monachus tropicalis has been so heavily exploited by humans that it is thought to be the only pinniped species to have become extinct in modern times. The Mediterranean monk seal Monachus monachus is a critically endangered species with probably only a few hundred individuals still alive today. They are secretive animals that are confined to remote areas and breed in caves. Despite being protected throughout their range Mediterranean monk seals are regarded as a competitor by fishermen who still kill them deliberately and cause their incidental death by entanglement in nets. A lack of food due to overfishing in the Mediterranean as well as loss of habitat and disturbance all threaten those remaining animals. A mass die-off event in 1997 resulted in the loss of a third of the population and plunged this species further towards extinction. The Hawaiian monk seal Monachus schauinslandi fairs best of all the monk seals but is still on the endangered list. Although it is heavily protected throughout its range it is estimated that fewer than 1,500 individuals exist today. It is most threatened by disturbance as humans move into its remote breeding grounds and the problem of entanglement in fishing nets and marine debris is as much a problem for this species as other marine mammals.
Four species of fur seal are listed as vulnerable on the IUCN Red List. The most recent survey in 1978 of numbers of Galapagos fur seals Arctocephalus galapagoensis estimated 40,000 individuals existed. It is not known how many Galapagos fur seals there are currently but the 1982-83 and 1997-98 El Nino events have severely depleted numbers due to the seals localised position and the lack of food during these events. The Juan Fernandez fur seal Arctocephalus philippii and the Guadalupe fur seal Arctocephalus townsendi were both thought to be extinct after intensive hunting but were rediscovered in the mid 1900s. Their total populations are thought to be 12,000 and 7,000 respectively. The total world population of northern fur seals Callorhinus ursinus is estimated at about 1,300,000 but these severely depleted numbers are still falling as hunting continues and other issues of pollution and entanglement take their toll.
The Steller sea lion Eumetopias jubatus is thought to number around 89,000, a drop from 290,000 in 1985, and has been placed on the endangered species list. The sharp decline, especially in western populations, is thought to have been caused by a reduced food supply, such as the walleye pollock, the result of intensive commercial overfishing of stocks. The Hooker sea lion Phocarctos hookeri found only in New Zealand is now classed as vulnerable and the Japanese sea lion Zalophus californianus japonicus has become extinct since 1988 when it was classed as endangered.
The Saimaa seal Phoca hispida ssp. saimensis is found only in Finland and thought to number about 200. This endangered animal is protected under Finnish law but its lake habitat is still threatened by human disturbance and pollution. The habitat of the Caspian seal Phoca caspica is also threatened by human activities, such as agricultural run-off and intensive oil production. It has been classed as vulnerable but its fate is far from certain.
The Atlantic walrus Odobenus rosmarus rosmarus is thought to number about 20,000 although accurate information is not available. Hunting caused the population to fall to this level and in 1995 it was estimated that 1,150 animals were still being killed each year, exceeding the sustainable yield. The Pacific walrus Odobenus rosmarus divergens is thought to fair better with a population size of 200,000 but again this figure is not accurate. Estimates of hunting-caused mortality since 1996 is thought to be about 6,000 animals a year.


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