What Do Otters Eat? River Otter Diet and Hunting

The river otter diet in detail

Scientists study otter diets mostly by collecting their droppings, called spraints, and identifying the fish bones, scales, crayfish shells and fur inside them. Hundreds of such studies across Europe and North America tell a consistent story: fish usually make up most of what river otters eat, often 60–90 percent or more, and the rest varies with the season and the place.

What do Eurasian otters eat?

The Eurasian otter is the otter of Europe, North Africa and much of Asia. On European rivers its favorite prey is often the eel, a fatty, slow-moving fish that hides under stones and roots at night. Salmon and trout, perch, carp-family fish such as roach and chub, and small fish such as bullheads and sticklebacks are also commonly eaten.

On the coasts of Scotland, Ireland and Norway, Eurasian otters hunt in shallow seawater among kelp and rocks, catching bottom-living fish such as butterfish, rocklings and sea scorpions, plus shore crabs. In parts of Britain, the spread of the invasive American signal crayfish has given otters a new and plentiful food source.

What do North American river otters eat?

The North American river otter lives in rivers, lakes, marshes and coastal waters across Canada and much of the United States. Like its Eurasian cousin, it mainly eats fish, and studies show it tends to catch slower, bottom-dwelling or schooling fish such as suckers, sunfish, carp, catfish and minnows rather than fast trout.

Crayfish are a major food in many areas, especially in summer. North American river otters also eat frogs, turtles, water birds, small mammals such as muskrats, and aquatic insects. Along the Pacific and Atlantic coasts, some otters feed on crabs, sea urchins and marine fish.

How do otters find and catch food?

Otters are underwater hunters, but they cannot hold their breath for long. Most hunting dives last well under a minute, so they hunt with many short dives in quick succession.

• Eyesight. In clear water, otters spot fish by sight and chase them with fast, twisting swimming.
• Whiskers. In murky water or at night, otters rely on their long, sensitive whiskers, called vibrissae. These pick up the tiny water movements made by a swimming fish or a crayfish in the mud.
• Feeling with their paws. Otters search under stones, among roots and in mud with their front paws, flushing out hiding prey.
• Teamwork, sometimes. North American river otters occasionally hunt in small family groups, which may help them herd fish. Eurasian otters usually hunt alone.

Small prey is usually eaten in the water. Larger fish are carried to the bank, a rock or the ice edge and eaten there, which is why fish remains and spraints often pile up at favorite feeding spots.

How much do otters eat?

Otters lose body heat quickly in water and have a fast metabolism, so they need to eat a lot. A Eurasian otter weighing 7–12 kg (15–26 lb) needs about 1 kg (2.2 lb) of food a day, roughly 10–15 percent of its body weight. North American river otters, at 5–14 kg (11–31 lb), eat a similar amount.

The sea otter of the North Pacific is a different case. Without blubber and living full time in cold seawater, it eats about a quarter of its body weight every day, mostly sea urchins, crabs, clams and mussels, and it famously uses rocks to crack shells; see do sea otters use tools?

Does the otter diet change with the seasons?

Yes. In winter and early spring, when fish are cold and sluggish, otters may catch more of them, but they also turn to frogs and toads gathering to breed. Eurasian otters often skin toads before eating them, leaving the poisonous skins on the bank. In summer, crayfish and young fish are plentiful. Birds and mammals tend to be eaten more when fish are hard to catch, for example when rivers flood or freeze.

Myths about what otters eat

Myth: otters empty rivers of fish. Otters live at low densities because each one defends a long stretch of water, and they mostly catch the commonest and slowest fish. In natural rivers, the number of fish depends far more on water quality and habitat than on otters. The real conflict is at garden ponds, fish farms and stocked lakes, where fish are crowded and easy to catch, and owners often use otter-proof fencing.

Myth: otters mostly eat salmon. Salmon are eaten where they are common, but most river otters live where eels, carp-family fish, perch, crayfish or suckers make up most of the menu. If you live in Britain, see are there otters in the UK? for where to watch them feed.