Wednesday 27 May 2020 is World Otter Day. To celebrate, explore the otterly fabulous world of the Eurasian otter with us. Not an animal you will see from your window, but if you are very lucky you might see evidence of otters on a walk by your local river or lake.

Measuring around a metre from nose to tail, the Eurasian otter, Lutra lutra, is one of our top predators in the UK. It is a member of the Mustelidae, the weasel family, so is related to stoats, weasels, pine martens and badgers. Otters are semi-aquatic and feed on a diet made largely of fish.

Take a look at the shape of our otters in the Museum. The head is broad and round with the eyes positioned on the top – this means that otters can swim around with just the eyes and little of its back above the water. Sensitive whiskers help them to detect prey even in murky waters. The body is long and finished with a conical, tapering tail. The legs are short and the feet are webbed. When swimming, an otter will propel itself through the water with its feet and use the tail like a rudder. When an otter dives, it is able to close its nostrils and ears to make sure water doesn’t get inside. Dives are short and shallow – an otter can only hold its breath for around 30 seconds.

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Otters have thick fur to keep them warm. To give you an idea of how dense their fur is: humans have around 100,000 hairs on their entire head, whereas a Eurasian otter has around 70,000 hairs per cm². This thick fur keeps the otter warm even when in water by trapping a layer of air near the body. Otters need to spend time grooming their fur, getting rid of any parasites they may have picked up. If an otter has been in salt water, this grooming time doubles because of salt crystals forming around the hairs as they dry causing them to stiffen and stick together in clumps, affecting the waterproof quality of their coat and its ability to trap air. Coastal otters need access to freshwater to wash the salt out of their coats.

Otters are shy, sensitive animals, so you are far more likely to see the evidence of an otter in the form of its footprints or spraint (droppings) than to see an otter itself. You can find information about these on the UK Wild Otter Trust website.

This species has a wide geographical range, including Europe, Russia, China, south Asia and north Africa. Eurasian otters are found from sea level up to highland streams, and have even been seen in the Himalayas. Otters need clean water, plentiful food, bankside vegetation in which to rest and groom, and suitable sites for their burrows (called holts). In the UK, otters are seen in both freshwater and coastal habitats. Did you know that there are even otters living in Cambridge? The local Wildlife Trust and Cambridgeshire Mammal Group have been working to monitor numbers of otters in Cambridgeshire.

Otter numbers have suffered major declines over the years. Water pollution has been a particular issue. Otters are at the top of the food chain, so they get a concentrated dose of pesticides and other chemicals that find their way into waterways. Add to that a loss of habitat, oil spills in coastal regions, roadside accidents and other threats. You can find out more about threats to otters with the IUCN’s Otter Specialist Group. The International Otter Survival Fund is working with Cardiff University to coordinate otter sightings and post mortems of otters found dead to investigate the presence of contaminants disease in UK populations.

The banning of certain pesticides and other conservation efforts have helped see an increase in otter numbers in Western Europe, but there is still work to be done.

Want to find out more about these wonderful animals? The Wildlife Trusts website is full of information, and check out the Our Changing Planet post on Conserving Britain’s Carnivores, which includes a talk by Dr Kate Sainsbury from our recent International Women’s Day celebrations.