Nerpa
From Wikipedia, the free encyclopedia
Order: Carnivora
Family: Phocidae
[Photo] Baikal Seal (Pusa sibirica). Date: 30 July 2005. Author Uryah (http://commons.wikimedia.org/wiki/User:Uryah). | Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". |
The Nerpa or Baikal Seal (Pusa sibirica) is a species of earless seal endemic to Lake Baikal, the world's largest fresh water lake by volume, located in Siberia near its border with Mongolia. Nerpa are unique among seals in several ways:
They and two subspecies of the Ringed Seal are the only seals to spend their whole lives in fresh water.
They are the longest-lived of seals (up to 56 years in females).
They feed their young on milk twice as long as other seals.
It remains a scientific mystery as to how the seals originally came to Lake Baikal, as it is hundreds of kilometres from any ocean, although it is speculated that they may have come at a time when a sea-passage linked the lake with the Arctic Ocean (see also West Siberian Plain). Like the Caspian Seal, they are considered to be related to the Ringed Seal of the Arctic.
The total population is estimated to be over 60,000 animals, and hunting was practiced widely in the past (officially and unofficially), but has been put under tighter restrictions recently because of declining numbers. Hunting Nerpa on the frozen Lake Baikal is a dangerous activity, and many such hunters drown every year.
Statistics
Weight: 70 kg average (150 kg maximum)
Length: 1.3 m average
Food: mainly golomyanka and gobies
Litter: usually one pup, sometimes 2
Diving Time: usually 20???25 minutes (45???60 minutes maximum)
Description
The Nerpa is one of the smallest true seals. The adult Nerpa, or Lake Baikal Seal, grows to be around 1.3 meters in length and can weigh from 63 to 70 kg. The animals show very little sexual dimorphism; the males are only slightly larger than the females. The seals have a uniform steely-grey coat on their backs and fur with a slightly more yellow tinge coating their stomachs. As the coat weathers, it becomes brownish. When first born, the seal pups are around 4.5 kg and have a coating of white silky natal fur. This fur is quickly shed and exchanged for a darker coat, much like that of the adult. Rare Nerpas can be found with spotted coats.
Distribution
The Nerpa lives only in the waters of Lake Baikal, on the edge of Siberia, the world's deepest freshwater lake and the largest by volume, accounting for 20% of the world’s freshwater. Baikal is 700 km long, 70 km wide and more than 1.5 km deep at some points. It is also several hundred miles inland, so it is something of a mystery as to how the Nerpas came to live there in the first place. It can be speculated that they swam up rivers and streams or that possibly Lake Baikal was linked to the ocean at one point as the result of a large body of water formed in a previous ice age. No one knows how they actually arrived at Lake Baikal, but it is estimated that they have been inhabiting that location for some 2 million years. The nerpa, Saimaa Ringed Seal Phoca hispida saimensis, and the Ladoga Seal Pusa hispida ladogensis are the only exclusively freshwater seals.
The areas of the lake in which the Nerpas reside changes depending on the season as well as some other environmental factors. The Nerpas are solitary animals for the majority of the year, sometimes living kilometers away from other Nerpas. In general, there is a higher concentration of Nerpas in the northern parts of the lake, because the longer winter keeps the ice frozen for longer, which is preferable for pupping. However, in recent years there have been migrations to the southern half of the lake. These are speculated to be evasive action against hunting. In the winter, when the lake is frozen over, they maintain a few breathing holes over a given area, and tend to remain to that area, not interfering with the food supplies of a nearby neighbour. When the lake begins to melt, the Nerpas tend to stay around the shorelines.
Abundance and trends
As of 2007, the Nerpa is listed as a “Lower risk” species on conservation lists. This means that while they are not currently threatened or endangered, it is possible and even likely that they will be in the near future. At last official count, the Russian government counted 104,000 Nerpas. That was in 1994. In 2000, Greenpeace performed its own count and came up with somewhere from 55,000 to 65,000 seals. It is thought that excessive hunting, as well as poaching and pollution is quickly reducing the Nerpa population. The main problem is excessive hunting.
In the last century, the kill quota for hunting Nerpas was raised several times, most notably after the fur industry boomed in the late seventies and when official counts began indicating that there were more Nerpas that previously known, allowing the kill quotas to be raised. The quota in 1999 was 6000 and was lowered in 2000 to 3,500 which is still nearly 5% of the Nerpa population if the Greenpeace count is correct. In addition, new techniques, such as netting breathing holes, and seal dens to catch the Nerpa pups have been introduced. In one area 3000 out of 4000 breathing holes had been netted, many probably illegally.
Unfortunately, for all of Lake Baikal, there are only 8 wildlife patrol officers, which amounts to roughly 2,500 square kilometers each. It is unlikely poachers will get caught. Even without poaching, hunting, even on a small quota, is a problem, because many of the seals that are shot or injured still escape, and die later. These do not fall under the kill quota and are tacked on after. Sadly, it is unlikely that poaching and hunting will slow considerably, at least not without government intervention. One prime seal pelt will bring 1,000 rubles at market, more than a month’s salary.
The other problem at Lake Baikal is the introduction of pollutants into the ecosytem. Pesticides such as DDT and Hexachlorocyclohexane, as well as industrial waste, mainly from the Baikalisk pulp and paper plant, have thought to have been the cause of several disease epidemics among the Nerpa. The speculation is that the chemicals work their way up the food chain, and weaken the Nerpa's immune systems, making them susceptible to diseases such as canine distemper and the plague, which was the cause of a serious Nerpa epidemic that resulted in the deaths of thousands of Nerpas in 1997 and 1999.
Reproduction
Female Nerpas reach sexual maturity at 3-6 years of age, whereas male Nerpas reach it around 4-7 years. The males and females are not sexually dimorphic. Nerpas mate in the water towards the end of the pupping season. With a combination of delayed implantation and a 9-month gestation period, the Nerpa’s overall pregnancy is around 11 months. Pregnant females are the only Nerpas to haul out during the winter. The male Nerpas tend to stay under the ice, in the water for all of winter. Nerpas usually give birth to one pup, but they are the only seal with the ability to give birth to twins. The twins will often stick together for some time after being weaned. The females, after giving birth to their pups on the ice in late winter will become immediately impregnated again, and will often be lactating while pregnant.
The Nerpas mate in the water, after the pups are born. Nerpas are slightly polygamous and slightly territorial, although not particularly defensive of this territory. Nerpa males will mate with around 3 females if given the chance. They then mark the female’s den with a strong musky odor, which can be smelled by another male if he approaches. The female raises the pups on her own; she will dig them a fairly large den under the ice, up to 5 meters in length, and more than 2 meters wide. Pups as small as two days old will then further expand this den by digging a maze of tunnels around the den. Since the pup will avoid breaking the surface with these tunnels, it is thought that this activity is mainly for exercise, to keep warm until they have built up an insulating layer of blubber.
The mother Nerpa will feed her young for around 2.5 months, nearly twice as long as any other seal. During this time, the pups can increase their birth weight (around 4 kg) fivefold. After the pups are weaned, the mother will introduce them to solid food, bringing shrimp, fish, and other edibles into the den.
In spring, when the ice melts and the dens collapse, the pup is left to fend for its self. Growth continues until they are 20 to 25 years old.
Every year in the late winter and spring, both sexes will haul themselves out and begin to moult their coat of fur from the previous year, which will be replaced with a new one. While moulting they do not eat and enter a lethargic state, during which time they often die of overheating, males especially, from lying on the ice too long in the sun. During the spring and summer, groups as large as 500 can form on the ice floes and shores of Lake Baikal. Nerpas can live to over 50 years old, exceptionally old for a seal, although they are presumed to be fertile only until they are around 40.
Foraging
The Nerpa’s main food source is the golomyanka, a type of sculpin that lives only in Lake Baikal. Nerpas eat more than half of the annual produced biomass of golomyanka, some 64,000 tons. They feed mainly at night, when the fish come within 100 meters of the surface. They feed with short, 10-20 minute dives, although this is hardly the extent of their abilities. Nerpas have two liters more blood than any other seal of their size and can stay underwater for up to 70 minutes if they are frightened or need to escape danger. Nerpas also eat some types of invertebrates, and the occasional omul, a staple of the diet of the people of lake Baikal.
The Nerpa is blamed for drops in omul numbers; however, this is not the case. The omul’s main competitor is the golomyanka and by eating tons of these fish a year, Nerpas cut down on the omul’s competition for resources.
Nerpas do have one unusual foraging habit. In the early autumn, before the entire lake freezes, the Nerpas will migrate to bays and coves and hunt out Sculpin, a fish that lives in silty areas and as a result usually contains a lot of grit and silt in its stomach. This grit scours out the innards of the Nerpa and gets rid of parasites.
http://en.wikipedia.org/wiki/Nerpa
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