Pusa caspica
One of the smallest seals alive, and the only marine mammal in a sea with no way out.
The Caspian Sea is the largest enclosed body of water on Earth. It has no outlet to any ocean, its water is brackish rather than fully salt, and it sits in the middle of a continent, bordered by Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan. A seal living there is a genuine puzzle, because seals evolved in the sea and there is no route in.
The answer is written in the skull. The Caspian seal's bone structure closely resembles the Baikal seal's, and both resemble the ringed seal, an Arctic species. The current interpretation is that ringed seals moved south roughly two million years ago along ice-age waterways connecting the north to what is now central Asia, and were left stranded when those connections closed.
That leaves two small, isolated relatives of the same Arctic seal, one in the Caspian and one in Lake Baikal, thousands of kilometres apart and completely cut off from each other and from the sea. Both ended up smaller than their Arctic ancestor, which is a common outcome for animals trapped in a confined environment.
The Caspian is deep and comparatively warm in the south, and shallow in the north. In winter, only that shallow northern end freezes, and that ice is where every Caspian seal pup is born. Females haul out in late January and February, give birth to a single white-coated pup, nurse it for about a month, and mate again shortly after weaning.
When the ice melts in late April, the entire population moves south into deeper, cooler water for the summer. This annual north-to-south migration means the whole species depends on one specific, shallow, seasonally frozen corner of one sea.
Their diving is modest and suits an inland sea. Typical dives run to about 50 metres and last roughly a minute, with rests at the surface in between. In autumn and winter they eat sculpins, gobies and crustaceans in the northern shallows; in summer in the south they take herring, roach, carp, sprat and smelt. An adult eats two to three kilograms of fish a day, close to a tonne a year.
A hundred years ago there were well over a million Caspian seals. Commercial hunting for oil and pelts took hundreds of thousands across the twentieth century, and pups on the ice were the easiest targets of all. A population that loses its young year after year declines even while the adults look perfectly healthy.
Hunting was only the opening pressure. The Caspian receives the outflow of some of the most industrialised river basins in Europe and Asia, and the seals, sitting at the top of the food web, accumulate heavy metals, organochlorine pesticides and radionuclides in their blubber. Between 1998 and 2000, zinc and iron concentrations in the tissues of dead, diseased seals rose sharply, and there is evidence linking contaminant load to weakened immune systems.
The consequences arrived as disease. In 2000, a morbillivirus outbreak killed large numbers of seals across the Caspian, and necropsies found pneumonia, encephalitis and pancreatitis, the classic lesions of distemper. In December 2022 another die-off was reported on the Russian coast, with initial counts of 700 dead revised upward to about 2,500. The cause of that one has not been established. The recorded pregnancy rate has fallen to around 30 percent, which is very low for a seal.
Ask how many Caspian seals are left and you will get answers anywhere between 70,000 and 300,000. That is not carelessness. It reflects a real methodological argument, and it is worth understanding rather than papering over.
Counts come from aerial surveys of ice-breeding females and of moulting haul-outs, mostly in the Kazakh and Russian sectors. The total depends heavily on assumptions: what fraction of females breed in a given year, what fraction of the population was out on the ice when the plane flew, how much of the sea was actually surveyed, and how that surveyed area gets scaled up. Change those assumptions and the answer moves by a factor of four.
Kazakh and Russian survey programmes running from 2020 to 2024 report a stable population near 270,000 to 300,000. The Caspian Seal Research and Rehabilitation Centre put the total below 70,000 in 2022. Independent specialists have said publicly that they regard 300,000 as closer to a rapid assessment than a precise estimate, and believe the real number is lower. The IUCN's Endangered listing, from 2016, rests on a figure of roughly 104,000 to 168,000 animals. All of those numbers are in print at the same time. What is not disputed is the long-term trend: the population has fallen by around 90 percent since the early twentieth century.
The pressure on Caspian seals today is different from the pressure a century ago. Icebreaker routes serving oil and gas operations pass directly through areas where pups are concentrated on the ice. Coastal development at Kenderli Bay, a documented migration stopover, threatens haul-out habitat. Bycatch in fishing nets kills an unknown number every year, and sea eagles take a substantial share of pups.
Behind all of it sits a larger problem. The Caspian Sea is shrinking and warming. The northern shelf is very shallow, so even a modest drop in sea level erases a large area of habitat, and warmer winters mean less ice, later ice, and thinner ice on the only breeding ground the species has.
The Caspian seal cannot move. There is nowhere else to go. Every conservation option, from protected areas to bycatch reduction to controlling industrial pollution, has to work inside the boundaries of one sea shared by five countries.
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