Vertebrate Zoology - V. M. Konstantinov 2011

Chordates
Terrestrial, or Four-Legged, Vertebrates — Vertebrates with Embryonic Membranes
Class Mammalia, or Mammals — Subclass Theria — Suborder Anthropoids, or Monkeys — Order Pinnipedia

Pinnipeds comprise 30 species of large marine mammals (body weight ranging from 40 kg to 4 t) that are systematically very close to carnivores and undoubtedly represent a branch of the latter that has adapted to an aquatic lifestyle. Pinnipeds spend the major part of their lives in the Water, where they feed and rest. They typically haul out onto land or ice only for mating, giving birth, and molting. Attachment to land varies among different species. In adaptation to their aquatic life, pinnipeds exhibit A number of distinctive morphological features. The overall body shape is elongated and fusiform; the neck is shortened and lacks a sharply defined constriction. The limbs are shortened and modified into flippers, while the coat is reduced to varying degrees. Subcutaneous fat deposits are exceptionally well developed, serving as thermal insulation, protecting the body against mechanical injury, and reducing the animal's overall density.

Most species lack external pinnae, yet their Hearing is exceptionally acute. Certain species have been proven capable of echolocation while swimming under ice and foraging. Pinnipeds produce faint underwater sounds (clicks), which are likely used for short-range localization. In the sea lion, the duration of each pulse is 3 — 5 ms, with a pulse frequency ranging from 3 to 13 kHz, averaging 7.5 kHz. Olfaction is well developed, whereas Vision, by contrast, is poor. The dentition is fundamentally similar to that of terrestrial carnivores, though dental differentiation is less pronounced.

Pinnipeds are of immense commercial importance. Their blubber and hides are widely utilized, and certain species yield valuable pelts (Fig. 201).

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Fig. 201. Pinniped species:

1 — harp seal (male); 2 — male fur seal (bull); 3 — harp seal (female) with newborn pup; 4 — walruses

The family Otariidae (eared seals) includes species that deviate the least from terrestrial carnivores. They possess rudimentary external pinnae. Their hind flippers can be rotated forward to serve for terrestrial locomotion, and their canines are well developed. This family comprises sea lions, Steller sea lions, and fur seals. All these species avoid ice and haul out on shores for reproduction.

Of greatest interest is the fur seal (Callorhinus ursinus). This large seal (up to 2 m in length) is distributed across the northern Pacific Ocean. In summer, from May to August, fur seals congregate at certain islands, where they breed and molt on the shores; these gatherings are known as rookeries. In autumn, having completed their molt, fur seals migrate southward. In our region, fur seal rookeries are located on the Commander Islands and Tyuleniy Island (off Sakhalin). Fur seals are polygynous: ashore, adult males gather harems of 30 — 80 females around themselves, which they fertilize. Females give birth to a single black pup. Adult fur seals possess a grayish-brown coat consisting of a dense, short underfur and sparse, coarse guard hairs. During fur Processing, the guard hairs are removed, while the underfur is sheared and typically dyed black. Fur seal harvesting is conducted in summer on the rookeries on a scientific basis that ensures population growth. Other fur seal species are found in the seas of the Southern Hemisphere.

The family Odobenidae (walruses) includes only a single extant species (Odobenus rosmarus), which has a circumpolar distribution and remains year-round along the coasts of Eurasia and North America, as well as islands of the Arctic Ocean, such as Franz Josef Land. Walruses reach a body length of 3 — 4 m and a mass of about 1 000 kg. Their hind flippers, much like those of eared seals, can be tucked forward and used in terrestrial locomotion. External pinnae are absent, and the Hair coat is strongly reduced. The upper canines are enormous, taking the form of massive tusks, which walruses use to haul themselves onto ice and to dig up benthic invertebrates from the seabed for food. Walrus haul-outs, sometimes quite large, occur on both shores and ice floes. The total population of walruses is substantial only in certain areas, and commercial hunting is permitted exclusively to indigenous peoples.

The family Phocidae (earless or true seals) is characterized by the absence of external pinnae; the hind flippers cannot be rotated forward and are permanently directed backward, taking no part in the locomotion of the animals across a solid substrate. The pelage of adults lacks underfur. A significant number of species within this family are distributed predominantly in the icy seas of both hemispheres. For molting, mating, and pupping, they usually haul out onto ice rather than land, forming large breeding aggregations known as wheezing grounds.

Some species are highly migratory, whereas others are more or less sedentary. The former group includes the harp seal (Pagophilus groenlandica). In summer, these seals inhabit the edges of the Arctic pack ice, migrating southward in winter to form breeding aggregations on the ice near Newfoundland and Jan Mayen, as well as in the funnel and throat of the White Sea. Here the seals mate, give birth, and molt, which is when the hunt takes place. The young are born with a thick, white coat of fur that persists for three weeks. Their diet consists of fish.

The large (over 2 m) bearded seal, or lakhtak (Erignathus barbatus), leads a sedentary lifestyle, frequenting shallow coastal waters of the Arctic Ocean, the Bering Sea, and the Sea of Okhotsk. It feeds on benthic invertebrates, does not form large aggregations, and gives birth on the ice. The small ringed seal (Phoca hispida) is likewise sedentary across most of its range. It is circumpolarly distributed throughout the northern Atlantic, the Arctic Ocean, the northern Pacific, and additionally in Lake Ladoga and Lake Saimaa. In winter, it typically constructs lairs in the ice where it pups. Distinct seal species closely related to the ringed seal inhabit Lake Baikal and the Caspian Sea. Ringed seals feed primarily on fish and crustaceans. Their pups are covered in thick, fluffy white fur and are referred to as whitecoats. A number of peculiar true seal species are known from the seas of the Southern Hemisphere, among them the crabeater seal (Lobodon carcinophaga), the leopard seal (Hydrurga leptonyx), and others.