Spotlight on.. Otter

The Iconic Otter

Although the otter is one of the UK’s larger mammals present in Oxfordshire and Berkshire and a very popular part of our culture, there won’t be that many of you who have seen one in the wild. Those of you who have are very lucky indeed because they generally keep a low profile and are most active, feeding at dawn and dusk.

“Our” otter is an Eurasian otter (Lutra lutra). It is an aquatic mammal, and in the UK, it lives along rivers and streams, in reed beds, and (in Scotland) along the coast. It eats a diet consisting almost exclusively of fish and large crustaceans (crayfish, crabs etc). However, like most animals it is an opportunist and won’t turn down the chance of catching an unwary water bird (for example). It mostly catches bottom-dwelling prey. This is why the ubiquitous American crayfish has become an important part of their diet in this area.

Otters are solitary creatures and the males and females only meet to mate. Any other meetings are likely to be aggressive! Being an otter is a complex business, you need to be able to exploit your environment successfully in order to survive, and cubs often stay with their mother for more than a year “learning the ropes”. They have large feeding areas (territories). A male otter may use more than 20km of river/stream. As they can’t be everywhere at once, they mark their territory with spraints (poo) to let other otters know.

Where are otters?

The Great Otter Recovery

Until the mid to late 1950s, otters were widely distributed and relatively common. Then suddenly they suffered a huge population crash. Ironically, this was first noticed by the otter hunts in the south-west of England. The reason behind this was traced to organochlorine pesticides (Dieldrin, Aldrin etc.) that had been introduced into the country after WWII. These chemicals got into species at the base of the food chain (aquatic invertebrates etc.) which were eaten by fish which were, in turn, eaten by otters. The effect was to concentrate the pesticides in the food the otters were eating, and it effected their fertility, soon knocking their population numbers.

The Environment Agency began national otter surveys in 1977 and have continued every 7 or so years. These surveys started to see an upturn in populations in the early 1990s after Dieldrin had been banned in 1981 and Aldrin in 1991. It’s been a dramatic return to health for the UK’s otter population. Here in the Thames Valley, we first saw otters returning on the Upper Thames, in the west of our region, in the mid 1990s and they have been spreading steadily eastwards since then. Below is a map of TVERC’s otter records for 1990-1999 compared with 2010 to 2019. Spot the difference!

Have you seen any otters?

If you spot any wildlife when you’re out and about, share your records and photos with TVERC. By letting TVERC know what you have seen you will help protect and improve your local environment by increasing the quality and quantity of data we hold.

Absence records are also very useful, so also let us know if you’ve been out and haven’t seen anything!

Your records can inform a variety of exciting biodiversity projects and help people make informed decisions about how to develop and manage land sustainably. We are a ‘not for profit’ organisation so rely on valuable help from skilled volunteers to improve our database.

Identification help

Otters are perfectly adapted for life in water. Their eyes are on the top of their head and they have ears which don’t stick out. This, together with their bullet-like shape and the fact that they swim very low in the water (with only the top of their head visible above water) means that they create very little disturbance in the water and can sneak up on their prey. They can also swim for several minutes under water. All this means that, for us, they are very difficult to spot. They also have very handsome whiskers that they use to detect movements in the water that might be prey.

The tail is conical, thick at the base and pointy at the end. This is the best thing to look for as no other animal has a similar tail. A mink, that is often mistaken for an otter, has a “toilet brush” tail!

Find out More

http://www.mammal.org.uk – The Mammal Society Website

http://www.otter.org/Public  - The International Otter Survival Fund Website

https://www.wildlifetrusts.org/otters - Downloadable guide to where to see wild otters

http://www.otterjoy.co.uk/otterplaces.html  - List of wildlife parks with otters

Books

Paul Chanin (1993) Otters, published by Whittet books – an excellent easy to understand book full of interesting information.

Woodroffe, G.L. (1994) The Otter, published by the Mammal Society – an informative booklet.

David MacDonald and Priscilla Barret (1993), Field Guide, Mammals of Britain and Europe, published by Collins.

Hans Kruuk (2006) Otters: Ecology, Behaviour and Conservation (OUP) – a very comprehensive, but still readable account.

Where should we direct our spotlight next?

If you are a recorder, a local recording group or just have an interest in a species, send us your suggestion for a species, along with some facts and a photo (if possible) to tverc@oxfordshire.gov.uk.