Pusa sibirica

17.

Baikal Seal

Pusa sibirica

French: Phoque du Baikal / German: Baikal-Ringelrobbe / Spanish: Foca del Baikal

Other common names: Lake Baikal Seal, Nerpa

Taxonomy. Phoca sibirica Gmelin, 1788,

“Baikal et Orom” (= Lake Baikal and Lake Oron, Russia).

This species is monotypic.

Distribution. lake Baikal in S Siberia, Russia.

Descriptive notes. Total length 130-145 cm (males) and 120-130 cm (females); weight 50-90 kg. Newborns are 60-65 cm in length and weigh c.4 kg. Baikal Seals are unspotted, or occasionally very sparsely and faintly spotted, with small heads and robust bodies. Claws on front flippers are relatively long, thick, and strong—evidently adaptations for living under the ice for much of autumn through spring when Lake Baikal freezes over and for helping them to get traction on the ice surface at pressure cracks and small breathing holes that they keep open. Offspring are born with a white lanugo (fine, soft hair) that is shed at 4-6 weeks old and replaced by shorter silver gray hair. Adult Baikal Seals are silver-gray to brown dorsally and yellowish white ventrally.

Habitat. Confined to freshwater Lake Baikal where they have been isolated from their Arctic marine ancestors for several hundred thousand years. Baikal Seals haul-out on island shorelines in summer but otherwise live on or under the lake’s frozen surface from autumn through spring.

Food and Feeding. Baikal Seals eat a large diversity offish, although the golomyankas or Baikal oilfish (Comephorus spp.) and Baikal sculpins (Cottocomephorus spp.) are their most important prey. Baikal Seals occasionally eat omul (Coregonus migratorius), a commercially harvested fish, in summer. Prey is captured mostly at depths of 10-50 m at night and 100-200 m during the day. In aquaria, Baikal Seals have been recorded to consume c.4-6% oftheir body weight/day, or ¢.5-6 kg offish.

Breeding. Mating of Baikal Seals occurs in water in late spring, just after offspring are weaned. Little is known about breeding structure of Baikal Seals, although they seem to be monogamous to promiscuous, with males searching for scattered receptive females in May when they are in estrus. After the egg is fertilized, it develops briefly and then attaches to the uterine wall about three monthslater, resulting in about eleven months of gestation. Females are sexually mature at ¢.3-6 years old. Pregnancy rates can vary from ¢.30% to 80-90%, depending on environmental conditions. Males are sexually mature at 7-10 years old. Offspring are born in snow and ice lairs from mid-February through late March and are nursed for ¢.2-2-5 months. Baikal Seals have a rather high rate of twinning (4% of annual births) compared with other seals. Maximum known age is 56 years for females and 52 years for males.

Activity patterns. Very little is known about behavior of Baikal Seals, particularly from autumn through spring when they are infrequently seen. Baikal Seals molt in late May-June and evidently fast during this period while hauled out on ice or island shorelines. Some individuals move southward as the lake begins to freeze in autumn and then northward again in spring as ice melts and recedes, although they can be found scattered throughout the lake in winter when they spend most of their time in the water or in concealed birth lairs during the breeding season. They appear to dive continually for several hours or more each day to depths of ¢.50 m at night and up to 200 m during the day to forage, with periodic periods of rest at the surface or hauled out during mid-day.

Movements, Home range and Social organization. Baikal Seals are mostly asocial and solitary, although they can aggregate on island beaches during summer when haul-out space is limited and in areas of high prey concentrations in spring and autumn.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Local Evenk and Buryat peoples hunted Baikal Seals for several thousands of years for meat and skins for clothing. Commercial harvests by Soviets began in the early 1900s when 2000-9000 Baikal Seals were killed each year through the 1970s, including up to 2000 recently weaned offspring. The population of Baikal Seals was estimated at ¢.77,000 individuals in the late 1970s and ¢.60,000 individuals in the mid 1980s: the decline was evidently due to excessive commercial harvests and some poaching for their pelts and meat, which was used to feed fur-bearing animals in production farms. Substantial declines in the late 1980s were related to mass mortality from an epidemic canine distemper-like virus. Numbers apparently increased to ¢.80,000-100,000 individuals by the mid-2000s, although ¢.2000 individuals are killed each year in a commercial harvest and another 1500-2000 individuals are poached or die after getting entangled in fishing nets.

Bibliography. Burkanov (2008), Grachev et al. (1989), Myazaki (2009), Ponganis et al. (1997), Stewart et al. (1996), Thomas et al. (1982).