The largest animals from the Mustelidae family that can be found in the Yamal region are the wolverine and the otter. Most otters live in the area up to the latitude of the Arctic Circle and spends part of its life underwater.

The otter is a dexterous fishing predator the size of a small dog. Its body length can vary from 55 to 95 centimeters, its tail is from 26 to 55 centimeters, and its weight is about 6 to 10 kilograms. It has a long, flat body and short, webbed feet. The fur color ranges from dark brown on top to light silver below. The guard hair is coarse, and the underfur is very thick and delicate — such fur does not get wet and protects the animal’s body from the cold well when it swims in icy water.

The otter lives in forest rivers, less often in lakes. It chooses places rich in fish and crayfish, where many small rodents live along the banks. Preference is given to rivers with pools and rapids that do not freeze in winter, which have the banks washed out by water and heavily littered with fallen tree trunks and branches, where there are many safe shelters and convenient places for burrowing. The otter also dens in caves, and sometimes just builds something like a nest in the thickets. Often the entrance to the animal’s shelter is under water.

Usually, a small section of the river with a length of two to six kilometers is enough for an otter to live in summer; it goes no further than 100 meters deep into the forest. In winter, if the fish stock becomes smaller and the holes freeze, the otter has to wander. Sometimes it crosses high watersheds: going down a steep slope, the otter presses its paws and rolls down right on its belly, leaving a trail in the form of a gutter. On ice and snow, the otter can walk up to 15–20 kilometers per day.

The otter feeds mainly on fish: carp, pike, and roach. In summer it catches water voles and other rodents, in some places it hunts waders and ducks. In winter, it eats frogs, caddisfly larvae.

Otters make a lot of sounds and are very sociable. They yap, hum and squeal, communicating with each other, chirping with pleasure during the game, calling their relatives with a squeak and shouting loudly during a fight.

Mating games take place mainly in March–April, after which the mating season begins. Pregnancy occurs with a latency period — a temporary delay in the development of a fertilized egg. It is highly dependent on local environmental conditions and climate, in particular, sudden changes in temperature, lack of food and other factors. In some individuals, the latency period can last up to 270 days. But the gestation period for otters is stable — about 63 days. Therefore, offspring can be born even in winter. The chances of surviving for such belated offspring are few.

But, as a rule, young otters are born from May to June. There are usually two cubs in a litter, but not more than four. Cubs begin to see clearly about 35 days after birth. Sexual maturity occurs in the second or third year of life.

The muskrat is native to North America and was introduced to Europe several times in the early 20th century. It came to the territory of Russia in 1926 and by the end of the 1940s, it became an important fur-bearing animal. Over time, this rodent settled across the vast territory of Northern Eurasia — from Western Europe to Mongolia, China and Korea.

The muskrat looks like a large rat. Its body can be 36 centimeters long, and its tail grows up to 28 centimeters. The animal weighs from 700 grams to 2 kilograms.

The muskrat has a strong round body, a short neck and a small head with a blunt muzzle. The ears practically do not protrude from the fur, and the eyes are small and set high — these are important adaptations for the semi-underwater lifestyle that she leads. The upper lip of the muskrat seems to be divided into two halves, through which the incisors can be seen. Due to this structure of the jaw, the animal dives deep and can bite through and eat underwater plants with a practically closed mouth, without choking.

On the front paws of the muskrat there are four long toes with large claws and one small one, with which it is convenient to dig the ground. There are five hind toes, with sharp long claws and membranes, thanks to which the paws look like flippers.

When the muskrat swims, it uses not only the membranes on its hind legs, but also its tail. It looks like a paddle and helps the animal to stay afloat. The muskrat also dives very well and can spend up to 17 minutes under water.

Muskrat fur consists of coarse guard hairs and soft undercoat and does not get wet in water. The rodent carefully looks after its fur: it constantly cleans it, combs and lubricates it with greasy secretions. Fur color can be brown, dark chocolate and sometimes black.

The muskrat loves to live in freshwater, but it can also settle in slightly swampy areas and lakes. Depending on the area where the animal lives, its dwelling has different characteristics. These can be burrows-tunnels with numerous winding corridors or huts on the surface, built of silt and vegetation.

The muskrat feeds mainly on plant food: aquatic plants and their roots, tubers, shoots of coastal shrubs and grasses. It loves reeds, horsetails, duckweed and sedge. Part of the rodent’s diet consists of animal food. The muskrat can fish for small fish, mollusks, frogs and crustaceans, and it also eats the remains of dead animals. In winter, the muskrat feeds on plant parts that are deep under water, its own supplies and sometimes it steals food from beavers' dams.

The life span of a muskrat in the wild is short — it is only three years. When it is looked after, this rodent can live up to 10 years.