Eurasian Otter (Lutra lutra): the Fisherman of the Danube Delta Channels

A V shaped ripple crosses the channel, a flat head with small ears rises for a second, looks at the boat, and slides under again with a curl of the tail. The Eurasian otter is the fisherman of the Danube Delta: a powerful swimmer, a patient hunter and one of the most elusive mammals of the reeds. Few animals are so present and so rarely seen, and every sighting is a small event on the boat.

Description

The otter has a long, flexible body, short legs and a thick, muscular tail that tapers to a point and works as a rudder. The head is broad and flat, with a blunt muzzle, long whiskers and small rounded ears set high on the head, so that eyes, ears and nose stay above the water while the rest of the body swims hidden. The fur is dark chocolate brown above and paler on the throat and chest, often with a cream patch under the chin that differs from one otter to another.

In the water you see mostly the head, a low back and the long tail, and the otter dives smoothly, often without a splash. Two other swimmers of the Danube Delta are often taken for otters. The muskrat is much smaller and swims slowly with its head and back above water. The coypu is about the size of a small otter, but it has a heavy, rounded head, bright orange front teeth and a thin, almost hairless tail, and it paddles on the surface instead of diving. The European mink, one of the rarest mammals of Europe, also lives here, but it is no bigger than a ferret, almost black, with a white chin and upper lip.

Built for the water

Everything in the otter is made for swimming and hunting under water. Its feet are webbed, and when it dives it closes its ears and nostrils. It has no layer of fat like a seal: the cold is kept out by its fur, one of the densest of any European mammal, with tens of thousands of hairs on every square centimetre. A short, very fine underfur traps a layer of air, and long guard hairs keep it dry. This is why otters spend so much time grooming and rolling on the banks: a dirty or oily coat would let the water reach the skin.

Under water the otter hunts with its eyes in clear water and with its whiskers in muddy water, feeling the movement of fish around it. Most dives last less than a minute. Fish make up most of its diet, especially slow fish living near the bottom and in the vegetation, but it also takes frogs, crayfish, water insects, sometimes small mammals and water birds. An adult needs roughly a kilogram of food a day.

Life along the channels

Otters live alone, except for mothers with cubs. Each one holds a territory along the water, which may stretch for several kilometres of bank, and patrols it regularly. They mark it with droppings, called spraints, left in visible places: a tree stump, a root above the water, a stone, a small mound on the bank. Researchers find otters more by these signs than by seeing them.

The den, called a holt, is hidden in the bank, among the roots of old willows, in dense reed or in a pile of driftwood, often with an entrance under water. Otters can breed at any time of the year. After about two months the female gives birth to usually two or three cubs, which open their eyes only after a month and stay with their mother for close to a year, learning to swim, dive and fish.

From fur to protection

Otters have lived beside people on the Lower Danube for thousands of years. Their bones were found in Neolithic settlements at Isaccea and Luncavița, more than 6,000 years old, in a cemetery of the Hamangia culture at Cernavodă, and in the Roman and Byzantine fortress of Halmyris, near Murighiol, where the garrison hunted otters for their fur, together with martens, foxes and beavers. In the medieval town of Noviodunum, at Isaccea, otter bones carry butchery marks: it was eaten.

In the 20th century its dense, water resistant fur made it a target across Europe. Hunting and water pollution brought the otter close to extinction in many countries, and in Romania estimates fell from about 3,200 animals in 1955 to about 1,700 in 1994. Strict protection changed the story. A review published in 2019 estimated 7,500 to 10,200 otters in Romania, and the Danube Delta, with its thousands of kilometres of channels full of fish, is one of its strongholds.

A survey carried out between 2019 and 2021 along the Danube between Isaccea and Tulcea and in the wetlands of Somova and Parcheș found more than 240 otter signs, and the highest density was right next to Tulcea, at the gate of the Danube Delta.

Interesting facts

• Fish on a fasting day. In the Middle Ages the otter was counted, together with the beaver, among the water animals, so Christian communities on the Lower Danube could eat its meat on fasting days, as if it were fish.
• Spraints that smell of tea. Fresh otter droppings are full of fish scales and small bones, but their smell is surprisingly pleasant. Naturalists have long compared it to jasmine tea or freshly mown hay, and it is the easiest way to tell otter signs from those of other animals.
• A whistle on the water. Otters talk to each other with high, thin whistles, especially mothers and cubs. On a quiet evening in the channels, this sound often gives them away before you see them.
• Every chin is different. The pale patches on the throat and chin have a different shape on each otter, and researchers use them to recognise individual animals in photographs.
• A strategy against the cold. Because it has no fat layer, an otter burns energy very fast in cold water. It hunts in short bursts and returns often to the bank to rest and dry its fur.

Status and threats

The Eurasian otter is listed as Near Threatened by the IUCN and is strictly protected in Romania and across the European Union, under the Habitats Directive. In the Danube Delta its numbers are good today. The dangers it still faces are fishing nets and fish traps, in which otters can drown, the pollution of water, and the loss of quiet, wooded banks where it can rest and raise its young. A Danube Delta with clean water, plenty of fish and undisturbed banks is all it needs.

When and where to see it in the Danube Delta

The otter lives in the Danube Delta all year round, and it can be seen in every season. It is most active at dusk, at night and in the first hours of the morning, and in quiet places it also fishes by day. Look for it along narrow channels with willows and fallen trees, on the edges of lakes, and wherever fish gather. In winter, when the lakes freeze, otters keep to the holes in the ice and to the flowing channels, and their tracks in the snow show where they go.

The best chances come from a slow, quiet boat early in the morning, when an otter may cross the channel in front of you or surface with a fish. On our 5 day wildlife photo tour and on the 5 day birdwatching tour in the Danube Delta we spend those early hours on the water. Read also about the raccoon dog, another quiet mammal of the reeds, or browse all the mammals of the Danube Delta and Dobrogea.