A
Otters have long, thin bodies and short legs ideal for pushing through dense undergrowth or hunting in tunnels. An adult male may be up to four feet long and weigh around 30 pounds. Females are typically smaller. The Eurasian otter has one of the smallest noses among otter species, with a distinctive shallow ‘W’ shape. The otter’s tail, often referred to as a rudder or stern, is thick at the base and tapers toward the tip, flattening out—this forms part of the propulsion system when swimming quickly underwater.
Otter fur consists of two types of hair: stout guard hairs that form a waterproof outer layer and a dense, fine under-fur that functions like thermal underwear. This fur must be kept in good condition through regular grooming. Saltwater reduces the fur’s waterproofing and insulation qualities. That is why freshwater pools are important for coastal otters. After swimming, they wash off the salt in these pools and then rub themselves dry against vegetation.
B
Scent is important for hunting on land, for communication, and for detecting danger. An otter’s sense of smell is likely similar in sensitivity to that of a dog. Otters have small eyes and are probably short-sighted on land. However, they can adjust the shape of the lens in their eyes to make it more spherical and thereby overcome water refraction. In clear water with good lighting, otters can hunt fish using sight.
The eyes and nostrils are located high on the head so that otters can see and breathe while mostly submerged. When underwater, otters hold their legs against their bodies except when steering, and they propel themselves using vertical undulations of the hind end. River otters have partial webbing on their digits, while sea and giant otters have more extensive webbing. The Asian short-clawed otter, which hunts shrimps in shallow water, has little to no webbing because strong swimming skills are not required for foraging in such environments. Otters also have small ears for streamlining, yet their hearing is very sensitive and protected by valves that close against water pressure.
C
A number of constraints and preferences limit suitable otter habitats. Otters require access to water, and rivers must be large enough to support a healthy fish population. Because they are shy and wary, otters prefer territories with minimal human activity. Additionally, a suitable area must be free of other resident otters—a concern that has resurfaced recently as populations begin to recover.
Coastal otters, with more abundant food, tend to occupy smaller ranges. Males often have territories that overlap with two or three females. Otters eat whatever they can catch—records show they eat sparrows, snakes, and slugs. Besides fish, common prey includes crayfish, crabs, water birds, and sometimes small mammals such as rabbits and even moles.
D
Eurasian otters breed at any time of the year where food is abundant. In colder regions like Sweden, where lakes freeze over in winter, cubs are born in the spring to ensure they grow before the next winter. In the Shetland Islands, cubs are typically born in the summer when fish is more plentiful.
Although otters can breed annually, not all do. Food availability is a key factor, along with territory and the female’s condition. The gestation period for Eurasian otters is 63 days, though species like Lutra canadensis may experience delayed implantation. Births usually occur in secure dens lined with soft bedding to keep the cubs warm while the mother is away feeding.
E
Otters usually give birth in dens lined with vegetation like reeds, grasses, and waterside plants. Litters typically range from one to five cubs. For unknown reasons, coastal otters often produce smaller litters. Cubs open their eyes at around five weeks, weighing approximately 700 grams. By seven weeks, they start eating solid food, and by ten weeks, they leave the nest. At three months, they enter the water and begin learning to swim. By eight months, they are able to hunt, though the mother still provides food. At nine months, the young otters are chased away by their mother, who then waits for the next breeding opportunity.
F
The British otter population faced dramatic decline during the 1960s. It wasn’t until the late 1970s that the main cause was discovered: the use of pesticides like dieldrin and aldrin, introduced in 1955. These chemicals, while persistent, were eventually linked to declining populations of birds of prey such as peregrine falcons and sparrowhawks. The pesticides entered rivers and accumulated in the food chain—from microorganisms to fish, and ultimately to otters.
Though phased out in 1962, the chemicals had long-lasting effects. Otter numbers continued to fall into the 1980s, due in part to habitat destruction and road deaths. Fragmented populations, weakened by the pesticide crisis, were vulnerable—just a few deaths could wipe out entire local populations.
G
Otter populations are now recovering across Britain. Numbers are increasing in the few areas where they survived and expanding into new regions. This progress is largely due to legislation, conservation work, habitat protection, and captive breeding programs.
Releasing captive-bred otters is controversial. Critics argue that if an area has suitable habitat, wild populations should recolonise it naturally, and if it doesn’t, the released animals will die. However, introducing otters into fragmented populations can provide the critical mass needed to stabilise and expand. This strategy worked in Norfolk, where the otter population had dropped to as few as 20 animals in the early 1980s. The Otter Trust’s breeding program helped reverse this trend and has since been discontinued—proof of its success and of the species’ improving outlook.