貝加爾海豹

**貝加爾海豹**（***Nerpa***）（***Pusa sibirica***，obsolete: ***Phoca sibirica***）係一種生活響西伯利亞貝加爾湖嘅海豹，唔單止係最細隻嘅海豹，重係世界上唯一生活響淡水水域嘅海豹。科學家認為佢哋係環斑海豹嘅部分祖先，喺幾百萬年前嚟到加爾湖之後，慢慢演化而成嘅。

## 統計

* *體重*：平均70公斤（155磅），最重150公斤（330磅）
* *長度*：平均1.3米（4尺3吋）
* *嘢食*：mainly golomyanka and goby
* *Litter*：usually one pup, sometimes two
* *潛水時間*：通常20至25分鐘（45至60分鐘最耐紀錄）

## 特徵
海豹公可生到1.3 米長（4 尺 3 吋），身體63至70公斤重（140 to 155 lb）。The animals show very little sexual dimorphism; 公大隻過乸少少。加爾海豹同其他海洋嘅親戚一樣，背脊灰褐色，然後向肚逐漸過渡為黃褐色，貝加爾海豹重有發達嘅前鰭同爪。

## 分佈
貝加爾海豹只住響貝加爾湖嗰度 

The areas of the lake in which the Baikal seals reside changes depending on the season as well as some other environmental factors. Baikal seals are solitary animals for the majority of the year, sometimes living kilometers away from other Baikal seals. In general, there is a higher concentration of Baikal seals 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 evade hunters. In winter, when the lake is frozen over, seals maintain a few breathing holes over a given area and tend to remain nearby, not interfering with the food supplies of a nearby neighbour. When the ice begins to melt, the Baikal seals tend to keep to the shoreline.

## Abundance and trends
2007年,貝加爾海豹被列作“lower risk”  即係表示佢哋This means that while they are not currently threatened or endangered, it is possible and even likely they will be in the near future. At last official count, by the 根據俄羅斯政府喺1994年嘅研究指出，貝加爾海豹數目大約有104,000隻。喺2000年，「綠色和平」(Greenpeace)用佢哋嘅方法數出佢哋大約得番55,000至65,000隻海豹。 It is thought excessive hunting, as well as less severe problems of poaching and pollution, are quickly reducing the population.

In the last century, the kill quota for hunting Baikal seals was raised several times, most notably after the fur industry boomed in the late 1970s and when official counts began indicating there were more Baikal seals than previously known. The quota in 1999 was 6,000, lowered in 2000 to 3,500 which is still nearly 5% of the Baikal Seal population if the Greenpeace count is correct. In addition, new techniques, such as netting breathing holes, and seal dens to catch pups have been introduced. In one area, 3,000 out of 4,000 breathing holes had been netted, many probably illegally. One prime seal pelt will bring 1,000 rubles at market, more than a month’s salary.

Lake Baikal has eight wildlife patrol officers, which amounts to one officer for roughly 2,500 square kilometers, making enforcement of regulations difficult. 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. It is unlikely poaching and hunting will slow considerably without government intervention.

The other problem at Lake Baikal is the introduction of pollutants into the ecosystem. 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 Baikal Seal. The speculation is that the chemicals work their way up the food chain, and weaken the Baikal seal's immune systems, making them susceptible to diseases such as canine distemper and the plague, which was the cause of a serious Baikal seal epidemic that resulted in the deaths of thousands of animals in 1997 and 1999.

## 繁殖
海豹乸到3至6歲時就到性成熟期。而公就要等到4至7年先到。 不論公乸The males and females are not strongly sexually dimorphic. Baikal seals mate in the water towards the end of the pupping season. With a combination of delayed implantation and a 9個月懷孕期。 gestation period, the Baikal seal’s overall pregnancy is around 11 months. Pregnant females are the only Baikal seals to haul out during the winter. The males tend to stay in the water, under the ice, all winter. Baikal seals 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. 

Baikal seals are slightly polygamous and slightly territorial, although not particularly defensive of this territory. 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 m (16 ft) )in length, and more than 2 m (6 ft) wide. Pups as young 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 Baikal seal 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 {9 lb}) 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 usually collapse, the pup is left to fend for itself. 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. Baikal seals 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.

## 食啲乜
貝加爾海豹主要食貝加爾湖嘅特產鮭魚，另外亦會食一啲無脊椎動物。佢哋主要喺夜晚搵食，花10至20分鐘時間潛水，然後等到啲魚游到離水面大約100米深嘅位置捉魚食。
The Baikal seal’s main food source is the golomyanka, found only in Lake Baikal. Baikal seals eat more than half of the annual produced biomass of golomyanka, some 64,000 tons. Baikal seals also eat some types of invertebrates, and the occasional omul. They feed mainly at night, when the fish come within 100 m (330 ft) of the surface. They feed with 10-20 minute dives, although this is hardly the extent of their abilities. Baikal seals 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. 

The Baikal seal 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, Baikal seals cut down on the omul’s competition for resources.

Baikal seals do have one unusual foraging habit. In the early autumn, before the entire lake freezes, they migrate to bays and coves and hunt 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 seal's innards and gets rid of parasites..

## Bibliography
* Peter Saundry. 2010. Baikal seal. Encyclopedia of Earth. topic editor: C. Michael Hogan; ed. in-chief: Cutler J. Cleveland. Washington, DC (Accessed May 21, 2010)
*Earth Island Institute.  “The Lake Baikal Seal: Already Endangered” (on-line), Baikal Watch. (Accessed March 6, 2004; archive.org link added August 25, 2010.)

## 資料來源

## 睇埋
*鰭足亞目
*海豹

## 出面網頁
*Harrold, A. 2002. “Phoca Sibirica” (on-line),  Animal Diversity Web. (Accessed August 27, 2007.)