Baikal seal ( Pusa sibirica )
|( Gmelin , 1788)|
The Baikal seal ( Pusa sibirica , Syn . : Phoca sibirica , Russian Байка́льская не́рпа , Baikalskaja Nerpa ) is an endemic seal of the Siberian Lake Baikal . It is the only seal species that lives exclusively in fresh water.
The baikal seal is a small species of seal. A body length of around 140 cm and a weight of 80 to 90 kilograms are given, extreme values are between 110 and 165 centimeters in length and between 50 and 130 kilograms. The dense fur is single-colored, dark silver-gray on the top and light gray on the underside, the unspotted, rarely indistinctly spotted fur is an essential feature of the species. The individual hairs are black at the base with a gray tip, which is why the animals appear wet State dark.
The body of the animals appears relatively broad, it is relatively shorter than that of the related species. The proportionally large head has unusually large eyes that dominate the proportions of the head. These are interpreted as an adaptation to the optical hunt in the very clear water of the lake. The tooth shape with pointed, mostly three-crowned molars and premolars is interpreted as an adaptation to the diet as a fish eater. The tooth formula is I 3/2, C 1/1, P 2/2, M 3/3 (34 teeth). The whiskers ( vibrissae ) are prominent and numerous (45 to 55), in addition there are 5 large vibrissae above each eye. The front extremities of the trunk are more powerful than those of the allied species, with powerful claws with a triangular cross-section; this is believed to be related to digging breathing holes in the ice.
Reproduction and life cycle
Baikal seals give birth to their young in pits they have dug themselves and in cracks on the ice sheet of the lake that has frozen in winter. The breeding areas are in the northern part of the lake, which, in contrast to the more southern parts, is shallow (water depth about 2 to 10 meters). The young are born on the ice sheet, which is still growing at this point, from around the end of January to the beginning of February, with a maximum in mid-March. The dams prefer ice 30 to 40 centimeters thick with cracks that allow access to the water. Only very rarely (less than 1 percent) are boys born on islands. The proportion of females reproducing annually is given as 88 percent. Baikal seals, like their relatives, have two nipples with mammary glands, so they can raise one or two pups. The proportion of twin births (two young animals) in this species is high for seals at 4 percent. The young animals are suckled on the ice for one and a half to two months, older young animals are also left alone longer by the mother while she hunts. While the mother animals are territorial on the ice, older young animals form large schools. The young animals are independent after three months at the latest.
The seal pups are around 65 centimeters long at birth and weigh between 1.5 and 4.5 kilograms (the lower numbers for twin births), they gain weight very quickly, around one kilogram per day. The seal pups wear thick white fur, which is interpreted as a cryptic color on the surface of the ice. The coat change to adult coat takes place after four to six weeks. The females need between four and six years to reach sexual maturity, the males seven years. According to measured growth strips in teeth and claws, only about ten percent of the population is more than 20 years old; the oldest individual found in the field reached an age of 56 years. The fertilization takes place in March or April in open water.
Male seals and non-reproductive animals do not go on the ice sheet but stay in the water. They make breathing holes to breathe, which they keep ice-free. Individual animals can create and maintain a main hole and up to ten secondary holes. Adult animals use the entire lake. When the ice melts, they join together to form larger groups of up to 1,300 animals on the remaining ice to change their fur. The rest of the year they live and hunt individually.
Way of life
The food of the Baikal seals consists exclusively of fish, among the 29 species known to be used mainly from Baikal oil fish and cottocomephoridae . In order to capture these, the seals usually dive 10 to 50, in extreme cases up to 300 m deep. The dives usually last 2 to 4 minutes, in extreme cases up to 40 minutes.
The Baikal seal is endemic to Lake Baikal. Only occasionally do individual animals migrate into the watercourses flowing towards the lake, but they never stay there for long. Very old information for the northeastern Lake Oron , which presumably goes back to the natural scientist Georg Wilhelm Steller , can no longer be interpreted today. Either the species is extinct there or there is a misstatement. Although other seals are found in freshwater (such as some subspecies of the ringed seal and the common seal ), the baikal seal is the only species that lives exclusively in freshwater.
Hazard and protection
The Baikal seal is said to have reached population sizes of around a million animals by the end of the 19th century. Excessive hunting is said to have reduced their population to 46,800 reproducing females (only these can be counted on the ice) in the late 1980s. A count from the aircraft and icebreaker in 2005/2006 showed an annual production of young animals in the order of magnitude of around 20,000 animals, which is slightly lower than earlier estimates. However, the population estimates are uncertain and depend on the intensity of the study and the method of counting. Earlier estimates were around 35,000 to 40,000 animals in 1967, 68,000 to 70,000 in 1978. In 2008, the IUCN's World Conservation Union ( IUCN) estimated the population to be around 80,000 to 100,000 animals, although fluctuating, but stable over the long term. The IUCN leads the Baikal seal in the Red List of endangered species so as not threatened ( Least Concern )
The most important predator of seal pups are eagle species, especially white-tailed eagles ( Haliaeetus albicilla ). In 2005/2006, 2,200 eagles were counted in the vicinity of the seal pups, which, roughly speaking, could capture ten percent of the seal pups. The wolf as another predator is probably less important. The baikal seal is susceptible to distemper , a viral disease that infected dogs transmit to the herd. In 1987/1988 between 5,000 and 10,000 Baikal seals were killed by the pathogen.
Baikal seals are known to be the top predators and are exposed to a high degree of environmental toxins such as polychlorinated biphenyls (PCB) or dichlorodiphenyltrichloroethane (DDT), which means that chronic damage to health such as damage to the immune system is assumed. Recently, it has been feared that the species will be threatened by changing ice dynamics as a result of climate change. However, the species was also able to survive earlier warm periods.
The baikal seal is still hunted today. The official hunting quota from 2004 to 2006 was around 2,000 animals; further losses through poaching or bycatch in the fishery of the order of 1,500 to 4,000 animals are assumed. Accordingly, far fewer animals are hunted than in the late 1970s (around 10,000) or the 1980s (around 4,000 to 8,000).
Since the beginning of November 2017, over 140 dead Baikal seals have washed ashore in the Irkutsk region in the south of Lake Baikal and in the neighboring Republic of Buryatia on the east bank. In order to get to the bottom of the phenomenon, several authorities set up a joint commission. So far, laboratory tests have not clarified the reasons. All that is known is that pathogens such as viruses have not been found. According to initial analyzes, the seals died from cardiac arrest. It was noticeable that the gastrointestinal tract of many specimens examined was empty.
Evolution, systematics, taxonomy
The status of the genus Pusa is still controversial, either as a separate genus or just as a subgenus of Phoca . Accordingly, the species is also called Phoca sibirica by numerous modern authors .
Since the discovery of the Baikal seal, it is a mystery how this species could have colonized Lake Baikal. The distance from Lake Baikal to the ocean ( Laptev Sea ) is around 2,000 kilometers as the crow flies, and over the Angara and Yenisei rivers even 3,800 kilometers. Lake Baikal is the oldest lake in the world and the region has not been reached by the sea since the Jura . The Caspian Sea , which is similarly isolated today, is home to a closely related endemic seal species, the Caspian seal . According to the first hypothesis, these inland seals are relic species of an earlier marginal sea, the Paratethys , which has now disappeared - they could therefore be of Miocene age. The other hypothesis assumes a much later re-colonization from the north during the middle Pleistocene , when huge shallow lake plates existed in Siberia during the Ice Age , which were dammed by ice dams.
Molecular pedigrees (based on the comparison of homologous DNA sequences) of the Baikal seal, Caspian seal and related species of the Phocidae such as ringed seal ( Pusa hispida ) and gray seal ( Halichoerus grypus ) did not produce clear results for a long time. According to initial results, even the monophyly of the genus Pusa appeared rather doubtful. According to more recent findings, these results are probably due to the close relationship and the as yet imperfect genetic splitting ("lineage sorting") of the species, as became apparent after several individuals of each species were included in the analysis. The most probable hypothesis is therefore that the species in the inland originated from the Arctic ringed seal during the Ice Age. The age of the species would therefore only be about 400,000 years. The fossil-proven seal species of the Paratethys such as Desmatophoca claytoni would therefore have died out without leaving any descendants.
As the last zoo in Europe, Leipzig Zoo held a female Baikal seal until 2013. Other attitudes are currently only known from Russia and Japan . In Japan, baikal seals are quite common. In April 2006, the world's first successful breeding of a baikal seal took place in the Niigata Aquarium.
- Ronald M. Nowak: Walker's Mammals of the World. 6th edition. Johns Hopkins University Press, Baltimore 1999, ISBN 0-8018-5789-9
- Thomas A. Jefferson, Marc A. Webber, Robert L. Pitman: Marine Mammals of the World. A Comprehensive Guide to their Identification. Elsevier, 2008. ISBN 978-0-12-383853-7
- Jeanette Thomas, Vladamir Pastukhov, Robert Elsner, Eugene Petrov: Phoca sibirica. Mammalian species No.188. published by the American Society of Mammalogists, 1982.
- Hideki Endo, Hiroyuki Sasaki, Yoshihiro Hayashi, Evageny A. Petrov, Masao Amano, Naoki Suzuki, Nobuyuki Miyazaki (1999): CT examination of the head of the Baikal seal (Phoca sibirica). Journal of Anatomy 194: 119-126.
- Tero Harkonen, Mart Jussi, Mirgaly Baimukanov, Anders Bignert, Lilia Dmitrieva, Yesbol Kasimbekov, Mikhail Verevkin, Susan Wilson, Simon J. Goodman (2008): Pup Production and Breeding Distribution of the Caspian Seal (Phoca caspica) in relation to human impacts. Ambio Vol. 37, No. 5: 356-361.
- IUCN Red List
- Victor B. Scheffer: Seals, Sea Lions, and Walruses: A Review of the Pinnipedia. Stanford University Press, 1958.
- Frances MD Gulland & Ailsa J. Hall (2005): The Role of Infectious Disease in Influencing Status and Trends. In John E. Reynolds III, William F. Perrin, Randall R. Reeves: Marine Mammal Research: Conservation Beyond Crisis. Johns Hopkins University Press 2005. ISBN 978-0801882555
- Marianne V. Moore, Stephanie E. Hampton, Lyubov R. Izmest'eva, Eugene A. Silow, Ekaterina V. Peshkova, Boris K. Pavlov (2009): Climate Change and the World's “Sacred Sea” —Lake Baikal, Siberia . Wellesley Biological Sciences Faculty Scholarship. Paper 2. online
- Endangered Baikal seals die by the dozen in a mysterious way . Neue Zürcher Zeitung , November 5, 2017, accessed on November 5, 2017.
- Jukka U. Palo & Risto Väinölä (2006): The enigma of the landlocked Baikal and Caspian seals addressed through phylogeny of phocine mitochondrial sequences. Biological Journal of the Linnean Society 88: 61-72.
- Ulfur Arnason, Anette Gullberg, Axel Janke, Morgan Kullberg, Niles Lehman, Evgeny A. Petrov, Risto Väinölä (2006): Pinniped phylogeny and a new hypothesis for their origin and dispersal. Molecular Phylogenetics and Evolution 41: 345-354. doi : 10.1016 / j.ympev.2006.05.022
- Tara Lynn Fulton & Curtis Strobeck (2010): Multiple markers and multiple individuals refine true seal phylogeny and bring molecules and morphology back in line. Proceedings of the Royal Society B 277: 1065-1070. doi : 10.1098 / rspb.2009.1783
- Tara L. Fulton & Curtis Strobeck (2010): Multiple fossil calibrations, nuclear loci and mitochondrial genomes provide new insight into biogeography and divergence timing for true seals (Phocidae, Pinnipedia). Journal of Biogeography 37: 814-829. doi : 10.1111 / j.1365-2699.2010.02271.x