The European Otter (Lutra lutra) also commonly known as theEurasian River Otter or Old Water Otter is the only species native to Britain(Devon Mammal Group, 2017). As a large, warm-blooded top predator, otters areprotected against many ofthe small-scale environmental factors that can have a considerable impact onthe survival of riparian invertebrates and plants (Chanin, 2003). However, in the 20th Century L.lutra was heavily impacted upon byanthropogenic contamination to rivers.
In 1978, a connection betweenthe decline in otter populations and widespread use of organochlorine pesticides infarming was identified resulting in full legal protection under Schedule 5 ofthe Wildlife and Countryside Act 1981 (Devon Mammal Group, 2017)Populationand DistributionThere has always been a stronghold of Lutralutra in Devon. L.lutra was once widely spread acrossEurope, however, Devon’s otter populations experienced a 75% decline in 1970,whilst across other parts of England experienced a 90% loss. Some populationswere also completely wiped out (Masons & Macdonald, 1994)Otter populations within Devon havesince recovered from their decline.
The populations are present on each of the county’s mainwatercourses, with the majority of available territories occupied (DevonMammal Group, 2017). Results from the National Otter Survey 2009-10, suggestthat Devon and Cornwall are the only counties in England where populations haverecovered close to pre-decline levels.Otter populations within Devon arefound on all of county’s major rivers: · The River Tamar – 61 miles long andforms the historic boundary between the counties of Devon and Cornwall.· The River Dart – Untwists its way down fromDartmoor to Dartmouth on the South coast of Devon.· The River Otter – Sourced in the county of Somersetnear Otterford then flows south for 32 km through East Devon to the EnglishChannel at the western end of Lyme Bay.· The River Plym – rises on Dartmoor and runs south to meet the River Meavy,then south toward Plymouth Sound .
· The River Taw – flows from a spring onthe central northern flanks of Dartmoor across north Devon to Barnstaple.HabitatRequirementsOtters are solitary and territorialand are regularly found next to flowing bodies of water. Otters mostly live along rivers buthave been found along lakes, streams, estuaries, canals, marshes and ponds.Adult otters have distinct territories where they reproduce, forage and rest. The territories are measured aslengths of river bank or coast. The sizes of individual territories depend onthe quality of habitat, amount of food and number of Holt sites available.
Male otters have considerably larger territories than female otters, which cancover up to 12 miles of the main river,overlapping into female territory. In Devon, the otter population is extremely close to carrying capacitytherefore competition fornew territories is high. Territorial behaviour in otters aids incontrolling the populationdensity by spacing out individuals.
It is also a way of avoidingover-exploitation of food resources.FeedingHabitsOttersare nocturnal and not very active during the day. Theyspend the majority of their time foraging for food, patrolling theirterritories and travelling to new locations. They are active and opportunistic hunters,searching and exploring weedbeds and tree roots along the water’s edge, preying on the easiestcatch or the most abundant. When otters feed they eatand move on. Their foraging behaviours prevent overfishing and overcrowdingalong the stretch of the river.
Otters primarily feed upon fish butare known to consume a variety of crustaceans, molluscs, frogs, birds and evensmall mammals. Their diet varies on the location and time of year due toresource availability. (In addition Otters undergo seasonal movements towards headwaters and upland marshes, takingadvantage of food resources available tohunt (Spawning frogs, salmon and sea-trout). Otters that hunt closer to the seaoften forage for bottom dwelling fish such as flounder and Pollack but theyalso hunt crabs.