BAIKAL SEAL

 

The Baikal seal, Lake Baikal seal or nerpa (Pusa sibirica) is a species of earless seal endemic to Lake Baikal in Siberia, Russia. Like the Caspian seal, it is related to the Arctic ringed seal. The Baikal seal is one of the smallest true seals and the only exclusively freshwater pinniped species. A subpopulation of inland harbour seals living in the Hudson Bay region of Quebec, Canada, (Lacs des Loups Marins harbour seals), as well as the Saimaa ringed seal and the Ladoga seal (both ringed seal subspecies), are also found in fresh water, but these seals are part of species that also have marine populations.

The most recent population estimates are 80,000 to 100,000 animals, roughly equaling the expected carrying capacity of the lake. At present, the species is not considered threatened.

Distinctive characteristics

The animals show very little sexual dimorphism; males are only slightly larger than females. Baikal seals are dark silver gray above and lighter yellowish grey on their undersides. They appear charcoal to black above when wet. Pups are born in a whitish lanugo that is shed at 4-6 weeks when they transition to a juvenile pelage that is lighter gray than adult coloration. Baikal seals are unmarked, having no rings or spots.

These seals are plump, with a proportionately wide body and a small delicate looking head. The eyes are proportionately large, forward set, and have a slight bulging appearance. The muzzle is small, wide, and delicate looking in juveniles. The vibrissae are long and prominent, including those over the eyes. The fore flippers are short, but broad, with heavy strong claws.

Measurements of Baikal seals have been taken as curvilinear lengths, which yield longer measurements than the standard lengths used for other species.

Dental formula    I 3/2, C 1/1, PC 5/5.

Size

Adult Baikal seals have been reported to reach approximately1.1- 1.4 m (3ft 7 in- 4ft 7in) in length and body mass 80-90 kg. New-born pups are 64-66 cm in length and 4-4.2 kg in weight.

Life Span

Adult Male can live up to 52 years; Adult Female can live up to 56 years.

Gestation Period    274 days.

Can be confused with

There should be no confusion; the Baikal seal does not share its range with any other pinniped species.

Distribution

Baikal seals are entirely confined to Lake Baikal and short distances up communicating rivers and streams. Most seals are found in the northern and central portions of the lake, and a portion of the population moves south in front of advancing ice that forms in the late fall and winter.

The origin of the Baikal seal is poorly known. They are believed to have made it to Lake Baikal sometime during Pleistocene glaciation events from northern Arctic Seas, and are derived from the ringed seal or a ringed seal ancestor. Baikal seals use islands and the rugged lake shoreline for hauling-out in the summer, and during other ice-free periods, and are ice living when the lake is frozen. They maintain breathing and access holes in ice, and give birth in snow-covered lairs excavated on lake ice. The twining rate of approximately 4% may be the highest for all pinnipeds. Pupping occurs from mid-February to the end of March, and pups are weaned in 2-3 months. Newly-weaned juveniles emerge from the lairs in April. Instrumented Baikal seals dove for 2-6 minutes, to depths of 10-50 m; the deepest dives were to 300 m.

Ecology and behavior

Female Baikal seals reach sexual maturity at 3–6 years of age, whereas males achieve it around 4–7 years. 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 nine-month gestation period, the Baikal seals' 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. Females usually give birth to one pup, but they are one of only two species of true seals with the ability to give birth to twins Very rarely, triplets or quadruplets have been recorded. The twins often stick together for some time after being weaned. The females, after giving birth to their pups on the ice in late winter, become immediately impregnated again, and often are lactating while pregnant.

Baikal seals are slightly polygamous and slightly territorial, although not particularly defensive of their territory. Males mate with around three 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 digs 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 then further expand this den by digging a maze of tunnels around the den. Since the pup avoids breaking the surface with these tunnels, this activity is thought to be mainly for exercise, to keep warm until they have built up an insulating layer of blubber.

Baikal seal pups are weaned after 2–2.5 months, occasionally up to 3.5 months. During this time, the pups can increase their birth weight five-fold. After the pups are weaned, the mother introduces them to solid food, bringing amphipods, fish, and other food 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 haul themselves out and begin to moult their coat from the previous year, which is replaced with new fur. While moulting, they refrain from eating 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 the females are presumed to be fertile only until they are around 30.

Predation

Baikal seals have few natural predators, but they do face threats from humans and smaller land predators. Brown bears, Red foxes, Sables and White tailed Eagles. Environmental issues of Water pollution And climate change.

Feeding and prey

Baikal seals forage extensively through the winter. Their diet consists primarily of several species of sculpins and golomyanka (genus Comephorus), but includes many varieties of freshwater fishes, including commercially important species.

Exploitation

The International Union for Conservation of Nature and Natural Resources (IUCN) classifies the Baikal seal as a species of least concern. The IUCN last assessed the Baikal seal in 2015, and the organization estimated the seal’s total population at between 80,000 and 100,000 animals, of which approximately 54,000 are adults. The seal is hunted by human beings, with hunts dating back roughly 9,000 years. Each spring the hunt culls 2,000–3,500 seals from the ranks of the population, most of which are pups; however, the hunt is largely viewed as sustainable. During the 1980s the species was stricken with an outbreak of canine distemper virus that claimed about a 10th of the population. Long-term threats, such as water pollution (which has exposed the seals to polychlorinated biphenyls [PCBs] and DDT) and the effects of climate change, are considered more pressing, however (see also global warming). As regional temperatures increase, it is expected that ice thickness and duration will decline, which could affect the seal’s breeding and feeding habits.

Threats and status

Subsistence and commercial hunting, and poaching continue. Several mass mortality events have been recorded. One event, attributed to a distemper virus in 1987-88, resulted in a large number of deaths. Baikal seals have high organ chlorine contaminant burdens due to industrial wastes discharged into rivers feeding the lake and bio-concentrating up the Lake’s food chain, and these pose an as-yet undetermined level of risk to the health of the population. Entanglement in commercial fishing nets accounts for an unknown level of annual mortality.

Factors hypothesized include

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

IUCN status    Least concern

A Young Seal