Caspian Seal
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| Pusa caspica (Gmelin, 1788) |
Caspian seals (Pusa caspica), one of the smallest members of the "true seal" family, are unique in that they are found exclusively in the brackish Caspian Sea. They can be found not only along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea. In winter, and cooler parts of the spring and autumn season, these marine mammals populate the Northern Caspian. As the ice melts in the warmer season, they can be found on the mouths of the Volga and Ural Rivers, as well as the southern latitudes of the Caspian where cooler waters can be found due to greater depth.
It is so-far unclear as to how these Seals became isolated in the landlocked Caspian Sea, and hypotheses have been put forth to explain this enigmatic situation. One of the most widely known hypotheses argues that the seals reached the Caspian during the Quaternary period from the north when continental ice sheets and proglacial lakes were growing. It may also be the case that the seals invaded this region during the late Pliocene cooling around 2 million years ago. It is generally thought that the Caspian seals, along with the Baikal seals (another isolated species of seals in a Eurasian basin), descended from the Ringed seal.
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[edit] Description
Caspian seals are known for their prominent spots, which are usually lighter on the females. Adults are approximately 1.5 meters in length and weigh around 86 kilograms. Displaying sexual dimorphism, the males of this species are generally larger and bulkier. Their heads are small relative to the rest of the body. The dental formula for these pinnipeds is I 3/2, R 1/1, PC 6/5.
Caspian seals are shallow divers, with diving depths typically reaching 50 meters and lasting about a minute, although deeper and longer depths have been recorded. They are gregarious, spending most of their time in large colonies.
After an 11 month gestation period, the single pups are born in January and February. Similar to other ringed seals, these pups are born with white pelage and weigh about 5 kilograms. Their white coat is molted at around three weeks to a month. Sexual maturity is reached at 5 years for females, and about 6 or 7 years for males.
[edit] Prey and Predators
Caspian seals diets varies seasonally, and includes a wide variety of fishes and crustaceans such as shad (Alosa spp), cyprinids, gobies, and crustaceans. The seals may enter river estuaries to eat carp, roach and pike-perch.
Sea eagles are known to hunt these seals, which results in a high number of fatalities for the juveniles. They are also hunted by humans for subsistence and commercial reasons. Due to the increasing industrial development in the surrounding region, pollutants and pesticides have entered the Caspian and caused significant habitat problems, weakened immune systems and contributed to disease outbreaks.
Since the late 1990s, there have been several cases of many Caspian seals dying due to Canine distemper Virus.
[edit] References
- Seal Specialist Group (1996). Pusa caspica. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Listed as Vulnerable (VU B1+2e v2.3)
