Zoological excursions

Baikal seal

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Mammals of Lake Baikal are represented by the only endemic species – the Baikal seal the whole life cycle of which is directly associated with the aquatic environment. The Baikal seal is a relict of the Tertiary fauna. The divergence time from the common stem of its ancestors is about 20 ky.
History of seal studies. Since ancient times the unique peculiar features of this animal have attracted the attention of researchers. The archpriest Avvakum and Nikolay Spafary, a Russian envoy in China (1675), were the first who informed about the presence of the seal in Lake Baikal. Studies on biology of the seal are first of all associated with such names as Gmelin (1733-1743), who was the first to give its scientific name to the seal – Phoca (Pusa) sibirica; Georgi (1764-1768) describing sizes and weight of mature individuals; B.I. Dybowski (1873) and Z. Svyatosha (1923, 1925, 1926) giving some information on biology of the seal. Their works, however, were of a fragmentary character. Systematic studies on morphology, biology, ecology and commercial hunting of Baikal seals were started by T. Ivanov (1938), N. Sviridov (1954), and V. Pastukhov (1993).
Structure. TheBaikal seal like all the animals of the order Pennipedia has a spindle-shaped body; the neck does not have marked boundaries from the body. The body length of an adult animal is up to 165 cm (from the tip of the nose to the end of hind flappers) weighing from 50 to 130 kg. Females are the heaviest animals; some of them have 80 kg of fat. The skin is covered with rather dense short (up to 2 cm) hairs. The edges of the hearing cover, a narrow ring around eyes and nostrils are hair free. The snout of the bull seal (mature males) of older age is almost bare. Flappers are covered with hair. There are webbings between fingers. There are strong claws on front flappers. Thin and rather long claws of hind flappers are weaker than the front ones.
Upper lips of the seal have semitransparent vibrissae (usually 8) arranged in regular rows. Near-mouth vibrissae in males are shorter than those in females. There are supraorbital vibrissae. Each “brow” consists of seven vibrissae: six vibrissae are located in a form of a circle and the seventh one is in the centre. Nostrils of the seal look like two vertical slits; their outer edges form skin folds – valves. Nostrils and auricles remain tightly closed in the water. Nostrils are opened under the pressure of air released from the lungs.
Eyesight, hearing and sense of smell are well developed. Eyes of the seal have a third eyelid. The vertical pupil is able to widen. The iris is brown. When the seal stays in the open air, its eyes cannot remain open during a long period of time because of intense lacrimation.
The absolute lung volume of an adult seal varies from 3500 to 4000 cm3. While in the water, about 2000 cm3 of oxygen is retained in the lungs. Oxygen is supplied by blood to the organism at diving to large depths for a long period of time.
The thickness of fat cover varies from 1.5 to 12-14 cm. The thinnest fat cover is on the front flappers, head and neck. There is no fat on hind flappers. Mature males are less fat than females, as well as young seals compared to adults. Hypodermic fat layer preserves seal from heat loss (thermal insulation), smoothes the effect of changes of water pressure while diving and ascending to the surface. It is also a storage for nutrients (the seal can stand without food for a long time) and determines floatability of the animal due to which animals can stay on the water surface.
The seal moves in the water with hind flappers. The role of the front ones is unessential. The speed under the water is 7-8 km/hour. The seal dives to 400 m and is able to hold its breath for 40 min. The variety of movements is characteristic of the seal. The seal can hardly move or very slowly on hard substrate. On the ice it moves using its front flappers bending its body, and the seal jumps while running away from hunters.
Distribution. The main habitat of the Baikal seal is the lake pelagic zone. Sometimes it is met in sors and bays of the lake. Lake Baikal, unlike other lakes of the country, completely freezes every year. The average thickness of the ice varies between 50 and 140 cm. The main events in the life of the seal – the birth and breeding of pups – take place on the ice. Coastal stones are necessary for moult and rest.
Regroupings of seals accompanied by migration of seals from south to north take place beginning from the ice breaking (March-May) to complete clearance from the ice. All the animals including one-year-old pups begin moulting with the ice breaking. Animals need hard substrate for changing old faded fur for new shiny one. At this time of the year, the animal comes out to the ice very frequently.
The majority of animals migrate from Southern Baikal to much thicker ice in Central and Northern Baikal where the ice breaks and the areas of open water widen. At the beginning of ice breaking, the total amount of rookeries for seals is maximal, while at the end – it is minimal. The density of animals on the rookery changes vice versa: it is lower when there is much ice and it becomes higher when the ice breaks – the number of seals increases due to migration of new groups of animals.

The distribution of seals around the lake in summer is stipulated by intensive fattening of thin animals which lost their weight after reproduction and moult. From early June to late September, animals of different age of both sexes, moulting and faded, come out to the coastal stones forming rookeries. By September, animals come out to rookeries very frequently and the number of animals on these rookeries increases. The seal comes out to the coastal stones mainly for moulting. In summer, animals are basically dispersed around the whole lake. About 15% of animals are concentrated within the three-kilometre zone of Lake Baikal, while 85% are in the pelagic zone. If the ice thaws quickly and the seal cannot manage to moult on the ice, its aggregations are confined to certain places of the coast – rookeries which are on the Ushkany Islands, in Ayaya Bay, on Cape Pongonye, in the area of the Ledyanaya River, Capes Northern Kedrovy and Khoboy. From several tens to several hundreds of seals are observed on each of these rookeries. When the ice thaws earlier, there are thousands of animals.

The distribution of animals of different age depends on different types of food. Close to the shores there are young seals (one-year-old animals and immature animals of the age of 1-3 years), and farther from the coast – adults. Young seals, unlike adults, are unable to dive deep for a long time. Therefore, they feed upon benthic sculpins in the coastal zone, while adult seals feed upon pelagic crustaceans and fish in the open water of Lake Baikal. Therefore, in summer seals are not seen in heated shallow places (bays, sors, and near-delta areas). This is due not only to elevated water temperature but also to the absence of main food for seals – small fish golomyanka. In autumn, with the beginning of water cooling seals actively migrate to bays and sors, where ice is formed much faster than in the open parts of the lake.
Reproduction. The seal becomes mature at the age of 3-4 years. Pregnancy lasts for 11 months. Usually one pup is born. There are some cases when two or even three-four pups are born. Females lactate for 2-2.5 months, but it may be longer – 3-3.5 months. There was observed a dependence of suckling duration on the state of the ice cover. Lactation is shorter in the period of early ice breaking.
The birth of pups takes place in early February-March and even in the first ten-day period of April. They are born in lairs made of snow and ice with a spacious inner chamber connected with water by a large air hole. Lairs are located at distances of hundreds of meters from each other, sometimes – some kilometres. Pups of the seal are born with silver or silver-grey fur with juvenile hairs. Pups stay in lairs for 1-1.5 months. They manage to completely moult before the surface snow layer of lairs is broken down.
Air holes and lairs. The seal makes an air hole after the ice formation. While the ice is thin, the seal easily breaks it pressing with its face from below. Thicker ice (2-2.5 cm) is broken by the animal kicking it with its front flapper. When the layer of ice is 3-6 cm, the seal makes an air hole with its strong claws. The air hole diameter may reach 15-20 cm.
To see air holes among ice hummocks is a rare phenomenon. Usually the seal scratches holes not far from the hummock ridge (1.5-8 m) in the monolith smooth ice under the cone-shaped snowdrift. The hole is made not at once. At the beginning of making an air hole, the air breathed out by the seal is accumulated in the icy hemisphere. The seal can use these air bubbles for breathing as carbon dioxide is dissolved fast at low temperatures. Oxygen is diffused from the water. Air bubbles protect air holes from fast freezing on of the ice. The ice pierced with bubbles is destroyed much easier by claws. While the ice is getting thicker (from January to March), the seal is able to make other holes, including those in the ice of 1 m thick. The hole is of a cylindrical form and the air chamber in the snow above the hole has the same diameter as the hole.
Since the very birth, a lair for a newborn pup is first of all a reliable shelter from predators, as well as from overcooling. A peculiar microclimate is formed inside the snowy shelter because of the constant presence of a pup and a female during suckling. It is necessary to take into account that there is no connection of the lair with the environment for 1-1.5 months: the temperature inside the lair reaches zero or sometimes plus five degrees while outside it is 15-20ºC below zero. This fact favourably affects the growth of pups as fewer efforts are spent on heat exchange.
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The seal’s pup
The role of lairs is especially important in protecting young animals from birds of prey: carrion crows ubiquitously inhabiting the coasts of Lake Baikal and white-tailed eagles. Pups of the seal do not scratch the lair wall as they try to hide from light. They come outside when the roof of the lair falls. At that time, pups grow up and as soon as they feel danger they come down to the water where there are no enemies. Pups are not threatened by terrestrial predators – foxes, wolves or sables, as they stay in lairs and the latter are located far from the shore in the deep parts of Lake Baikal.
Females take great care of their brood. In case of danger a seal-mother carries its pup in teeth or in flappers and brings it to spare air holes which the female makes not far from the main hole in the lair. Females make air holes according to the following principle: the first hole is always located near the air hole of the lair (2-5 m), the next hole is at longer distance from the first one and so on. Distances between the farthest holes of the lair are the longest.
Males do not take any part in breeding of the pup. Appearing near lair holes of the breeding females during the rut (April), they disappear very quickly living separately near their holes usually located on smooth (without hummocks) areas of ice. Some of them, in particular those living in the western part of the lake, are grouped along the cracks near large holes. They may be seen among the animals of transitional age of both sexes. Wounds-scratches on the skin of pups are evident of the fact that males make the life of pups hard.
Feeding. The composition of food consumed by seals is determined by the analysis of the intestine content. Otoliths, ear bones of fish, which differ in structure, size and form in various fish, may serve as a convenient tool for identifying fish species consumed by the seal.
The seal can feed on pelagic representatives: small fish golomyanka (Comephorus dybowski and C. baicalensis), sculpins (Cottocomephorus inermis and C. grewinkii), omul (Coregonus autumnalis migratorius), crustaceans (Epischura and Macrohectopus), as well as on inhabitants of the littoral-slope zone: sculpins (Cottus kesslerii and Paracottus knerii), salmons (more often in nets), and benthic invertebrates (gammarids and molluscs). The food composition of the seal depends on the season. They feed intensively in summer during fattening.
Besides fish, gammarids can be found in the bowel of the seal which usually get to the seal from the bowels of swallowed fish. The seal can feed on Epischura and Macrohectopus if there are large aggregations of these animals. In the littoral zone, the seal feeds mainly at dusk upon benthic crustaceans (Acanthogammarus) and molluscs.
During the moult (from early May till early June), the feeding of adult animals and animals of the transitional age is weakened, as most of the time they spend on the ice and do not dive into the water even at high temperatures.
The seal usually lives under the water when the lake is covered with ice (December-early May). The whole population is located in the open Baikal. The seal spends a lot of energy in winter as it has to keep an air hole free from ice and to dive to large depths because the main mass of golomyanka and sculpins are located at depth of over 100 m. The seal also spends a lot of energy on heat exchange in the cold water. During this period, the migration of the seal is limited by the system of air holes, while the vertical migration (diving) of the seal – by the fish distribution at depths. The species composition of fish consumed is poor: Comephorus dybowski – 82%, Comephorus baicalensis – 10%, Cottocomephorus inermis – 7%, Cottus kesslerii – 0.3%, and omul – 0.1%.
In autumn, the percentage of golomyankain ratio of the seal is 2-3 times lower, whereas that of Cottocomephorus grewinkii, salmons and benthic sculpins and that of Cottus kesslerii and Paracottus knerii becomes 4 and 10 times higher, correspondingly. While feeding on Cottus kesslerii, a lot of sand and silt is accumulated in the stomach and bowel of the seal. With the help of silt and sand the seal is able to get rid of parasitic nematode, which affects the stomach and all the sections of the bowel causing ulcer formations.
In the experiment carried out in the specially equipped aquarium, it was established that every animal needed 2500 g of Cottocomephorus grewinkii a day. Under natural conditions, a lot of energy is spent on migrations. Besides, a flush of energy (food) is required for growth of animals. It means that the “total” average daily ratio should exceed 2500 g. The seal’s ratio of 3 kg is considered to be real. It is equivalent to 2100 kcal, which is in agreement with common conceptions on the level of energetic exchange in mammals with a predatory type of feeding.
Adaptation of the seal to Lake Baikal conditions. Unlike alpine and mountain lakes, the unique feature of the Lake Baikal ecosystem, which is located in the centre of the Asian continent, is that a representative of marine mammals – the seal - tops its food pyramid. The ecosystem of Lake Baikal approximates to the marine one, i.e. it belongs to the category of saturated (complete) ecosystems. The reasons which caused the appearance of significant differences between the Baikal seal and its closest relatives – a ringed seal and a Caspian seal – are as follows: large depths of Lake Baikal, the long period of the solid ice cover, stability of food resources, and peculiar features of distribution of the main objects of food in the water column, first of all, two species of golomyanka.
The seal adapts to the conditions of Lake Baikal due to its morphological and biological peculiarities. The position of the teeth with the increased number of additional apexes can be attributed to natural selection and results from feeding on small fish. Optic bulbs became larger because of feeding at depths with weak light and at dusk. Claws of front flappers are stronger because the seal makes air holes for breathing in the solid ice of about 1 m thick and keeps them free from ice. The elevated hemoglobin concentration in the blood is the result of deep-water dives for a long period of time in pursuit of food with the necessity of stopping breathing. The dispersion of seals around the water surface of the lake is attributed to the distribution of food resources and their density. The rate of weight and linear growth is getting higher (2-3 times) at the first year of life because of longer period of lactation, long period of solid ice cover, stable food resources, and breeding of pups in snowy lairs. The mortality rate at the first year of life decreases. Early maturation and high reproductive potential are observed in the seal. Hence, the seal is an integrated link, or the top of the food web in the Lake Baikal ecosystem.
From ancient times till nowadays the seal belongs to a valuable object of commercial hunting. This animal, playing the role of a commodity and an idol, initiated, to a considerable extent, the occupation of Lake Baikal coasts by a man. The seal provides with fur skins, fat of medicinal properties, and meat. At present, the total number of seals makes up 80-100 thousand individuals.
References
  • Ivanov T.M. Baikal seal, its biology and commercial hunting // Izv. Biol. Geogr. NII at East-Sib. State University. – Irkutsk, 1938. – P. 5-119/
  • Pastukhov V.D. Baikal seal. – Novosibirsk: Nauka, 1993. – 271 p.
 
 
 
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