While saltwater seals are major fixtures of many temperate coastlines around the world, their freshwater counterparts are indisputably rarer. Unless you live in some of the coldest nations of the northern hemisphere, it’s highly unlikely that you’ll catch a glimpse of one of these elusive creatures. They’re associated with just a few pristine lakes, all of which are known for being very chilly in winter.
Freshwater seals likely evolved from clades that were separated from their marine habitats. In fact, some of today’s modern saltwater seal populations may occasionally spend a portion of the year in coastal lakes. Some subpopulations have become geographically separated from the coast, forcing them to adopt a salt-free lifestyle.
As these animals make up just a few extant groups, their conservation is crucial. Warming temperatures and anthropogenic disturbances within or close to their habitats can significantly reduce their chances of survival. As they rely on fish and crustaceans as main sources of nutrients, the freshwater systems they inhabit must be kept free of toxic pollutants.
Freshwater Seals
1) Baikal seal (Pusa sibirica)
Of course, if just one of the world’s freshwater systems could have an isolated population of obligate freshwater seals, it would be Lake Baikal. The largest lake in the world in terms of freshwater volume, this deep and markedly old Siberian resource is extremely biodiverse. The Baikal seal is just one of hundreds of animals that are found only within its protected waters and along its icy coastlines.
With a paleo-hydrographic history that continues to baffle scientists, today’s Baikal seals seem to have ancestors that are shared with those of modern saltwater seals. Their populations may have been isolated from marine groups as early as 500,000 years ago. Today, tens of thousands of individuals inhabit the productive lake and may venture as far as a few hundred kilometers upstream.
Baikal seals are known for being quite small. Indeed, their largest individuals tend to measure just 1.4 – 1.6 meters (4.6 – 5.2 feet) long. They are distinguished by their uniform layer of deep-grey fur, which takes on a yellowish tinge on their bellies. They feed on thousands of tons of Lake Baikal’s oilfish, whitefish, and sculpin populations. In seasons with minimal fish, they may also feed on amphipods.
P. sibirica is classified under ‘Least Concern’ in IUCN’s red list, though their numbers appear to be in decline. They continue to be hunted for their meat, pelt, oil, and for souvenirs. Unfortunately, some tourists are primarily drawn to the lake by the chance to legally hunt for seal pups. This highlights the grim reality that plagues many of the world’s rarest species – that some people will stop at nothing to hold power over nature’s treasures.
2) Caspian seal (Pusa caspica)
The Caspian seal favors the brackish waters of the Caspian Sea, but its subpopulations may routinely enter purely freshwater tributaries like the Volga River and Ural River. Its ancestors likely diverged from taxa that occupied Arctic waters and may have moved inland via connecting rivers. A study that looked into this species’ skull morphology suggests that it may be closely related to the Baikal seal, which is likewise a member of the Phocidae family of earless seals.
Caspian seals are found along lake shorelines, on rocky outcrops, on islands, and on floating ice. Where they situate themselves is largely influenced by ambient temperatures and by the presence of ice. Compared to Baikal seals, they are even smaller! Their adults max out at just 50 inches (1.3 meters) long, making them some of the most adorable members of the pinniped world.
Able to skillfully dive to depths of about 164 feet (50 meters), Caspian seals feed on a diversity of ray-finned fishes and crustaceans. Those that venture into estuaries feed on large amounts of freshwater fishes, crabs, and shrimps. As they are apex predators all throughout their native range, they unfortunately tend to bio-accumulate heavy metals and other toxic pollutants.
3) Iliamna Lake seal (Phoca vitulina richardsi)
A subspecies of the harbor seal, the Iliamna Lake seal has a landlocked population in Alaska’s largest body of freshwater. Once traditionally hunted by indigenous groups, this freshwater pinniped is perceived as fatter and larger than the typical harbor seal in coastal habitats. A geographically isolated taxon, it is now classified as endangered and is federally protected under the Marine Mammal Protection Act.
Now extremely rare, the Iliamna Lake seal has a genetic history that lives on in just a few hundred individuals. Its small population is jeopardized by anthropogenic activities that can significantly alter the water quality of its sole habitat. Proposals of projects like pebble mines, supposedly to exploit Alaska’s gold and copper deposits, could lead to its extinction.
Iliamna Lake’s seal population relies on seasonal sockeye salmon runs to sustain its nutrient requirements. This means that commonplace problems like climate change, damage to estuaries and rivers, and eutrophication also severely affect its feeding success. As the only freshwater seal in the US, it may serve as a bioindicator of the water quality of southwestern Alaska’s wetlands.
4) Ladoga ringed seal (Pusa hispida ladogensis)
Lake Ladoga is a large freshwater system in northwestern Russia, where it is connected to thousands of rivers. Its population of endemic seals is composed of around 2,000 – 3,000 individuals. Valuable components of the lake’s ecology, these seals serve as apex predators. They help maintain a well-balanced food chain by feeding on a wide range of native fish species.
Ladoga seals belong to a fairly isolated subpopulation of the Arctic ringed seal (P. hispida). Their ancestors likely separated from their coastal populations during the last ice age. Considered a “post-glacial relic”, this species is unfortunately becoming more scarce. Its numbers have dramatically dwindled over the course of the last century.
In summer, Ladoga ringed seals congregate, sometimes forming haul-out herds with up to 50 seals, in the northern part of the lake. Able to live for about 30 – 35 years, they sport either a deep or light-brown patterned coat. These have seemingly random arrangements of rings and spots. Their pups, which weigh around 8 – 11 pounds (4 – 5 kg) at birth, are threatened by illegal poaching, net entanglements, and toxic pollutants.
5) Saimaa ringed seal (Pusa hispida saimensis)
Essentially, the Saimaa ringed seal falls under the same taxonomic group as the Ladoga ringed seal. Though Lake Saimaa (located in Finland) is connected to Russia’s Lake Ladoga via the Vuoksi River, subpopulations of their Arctic ringed seals don’t mix. Those in Saimaa have been genetically isolated for thousands of years, so they have subtle yet distinct morphological differences from Lake Ladoga’s seals.
The Lake Saimaa freshwater system consists of several basins with interconnecting streams. Though it is quite shallow, with depths averaging at around 56 feet (17 meters), it is home to thousands of small islands. In winter, much of the lake freezes over to create a maze-like, icy habitat. Summer temperatures permit the flow of water from one basin to another, allowing ringed seals to breed and comfortably shed their old coats.
Despite the natural complexity and diversity of Lake Saimaa, its pinniped populations are at high risk of extinction. Only about 400 seals are estimated to remain in its cool waters. Net fishing, insufficient ice and snow cover, and climate change are some of the major threats to their survival. These excellent divers struggle to recover from declining populations as they breed only once per year.
6) Ungava seal (Phoca vitulina mellonae)
The Ungava seal is Canada’s only freshwater pinniped. It is restricted to a network of lakes found in the northern reaches of Quebec. This endemic carnivore, a subspecies of the harbor seal, is extremely rare – recent findings suggest that there may be just 50 to 100 Ungava seals left! Classified by the IUCN as an endangered species, its remaining population is threatened by habitat alteration, mining, fishing, and renewable energy production.
Once locally regarded as a source of meat and pelt, the Ungava seal unfortunately remains to be extremely elusive. Current trends on the state of its mature individuals are unknown due to data deficiencies. The Cree, which is a relatively populous indigenous group of Quebec, may still be harvesting these critically imperiled seals at low rates.
Can Saltwater Seals Live in Freshwater?
A fair number of saltwater seal species are able to enter freshwater environments in search of food. Harbor seals, for example, may swim into estuaries and as far inland as freshwater streams in hot pursuit of rapid schools of fish. The general decline in the quality of rivers may have influenced their preference for hunting in salty, highly energetic coastlines.
Unlike many other marine mammals, seals aren’t particularly sensitive to abrupt changes in water salinity. Though the majority of seal populations spend most of their lives in marine habitats, those with access to food-rich freshwater environments are likely to exploit them during key periods of the year. Occasionally, saltwater seals may get lost or trapped in freshwater zones and may struggle to find their way back to the coast. In most instances, however, they can be relied upon to instinctively navigate between varied water systems.
