the baikal seal（ 贝加尔湖海豹 ）的英文简介,做演讲用的材料,

the baikal seal（ 贝加尔湖海豹 ）的英文简介,做演讲用的材料,
the baikal seal（ 贝加尔湖海豹 ）的英文简介,做演讲用的材料,

the baikal seal（ 贝加尔湖海豹 ）的英文简介,做演讲用的材料,
来源 百科
The Baikal seal, Lake Baikal seal, or nerpa (Pusa sibirica, obsolete: Phoca sibirica), is a species of earless seal endemic to Lake Baikal in Siberia. Like the Caspian seal, it is related to the Arctic ringed seal. The Baikal Seal is the smallest of the true seals, and with the exception of a subpopulation of inland harbour seals living in the Hudson Bay region of Quebec, Canada (lac de loups marins harbour seals), they are the only exclusively freshwater pinniped species.

It remains a scientific mystery how the seals originally came to Lake Baikal, hundreds of kilometers from any ocean. Some scientists speculate the seals arrived at Lake Baikal when a sea-passage linked the lake with the Arctic Ocean (see also West Siberian Glacial Lake and West Siberian Plain).

The total population is estimated to be over 60,000 animals, and hunting of the seals, once widespread, is now restricted.
The Baikal seal is one of the smallest true seals. The adult grows to be around 1.3 m (4 ft 3 in) in length with a body mass from 63 to 70 kg (140 to 150 lb).[3] The animals show very little sexual dimorphism; the males are only slightly larger than the females.[3] They have a uniform, steely-grey coat on their backs and fur with a slightly more yellow tinge coating their abdomens. As the coat weathers, it becomes brownish.[4] When first born, pups are around 4.5 kg (9.9 lb) 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 Baikal seals can be found with spotted coats.
The Baikal seal lives only in the waters of Lake Baikal.[5] It is something of a mystery how Baikal seals came to live there in the first place. It can be speculated they swam up rivers and streams or possibly Lake Baikal was linked to the ocean at one point as the result of a large body of water, such as the West Siberian Glacial Lake or West Siberian Plain, formed in a previous ice age. The seals are estimated to have inhabited Lake Baikal for some two million years. The Baikal seal, the Saimaa ringed seal (Pusa hispida saimensis), and the Ladoga seal (Pusa hispida ladogensis) are the only exclusively freshwater seals.

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, possibly to evade hunters.[3] 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.
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.[4] Baikal seals also eat some types of invertebrates,[4] 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 the seals' gastrointestinal tracts and gets rid of parasites.