The European Otter (Lutra lutra) also commonly known as the
Eurasian 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 are
protected against many of
the small-scale environmental factors that can have a considerable impact on
the survival of riparian invertebrates and plants (Chanin, 2003).  However, in the 20th Century L.lutra was heavily impacted upon by
anthropogenic contamination to rivers. In 
1978, a connection between
the decline in otter populations and widespread use  of organochlorine pesticides in
farming was identified resulting in full legal protection under Schedule 5 of
the Wildlife and Countryside Act 1981 (Devon Mammal Group, 2017)Population
and DistributionThere has always been a stronghold of Lutralutra in Devon. L.lutra was once widely spread across
Europe, however, Devon’s otter populations experienced a 75% decline in 1970,
whilst across other parts of England experienced a 90% loss. Some populations
were also completely wiped out (Masons & Macdonald, 1994)Otter populations within Devon have
since recovered from their decline. The populations are present on each of the county’s main
watercourses, with the majority of available territories occupied (Devon
Mammal Group, 2017). Results from the National Otter Survey 2009-10, suggest
that Devon and Cornwall are the only counties in England where populations have
recovered close to pre-decline levels.Otter populations within Devon are
found on all of county’s major rivers: ·    The River Tamar – 61 miles long and
forms the historic boundary between the counties of Devon and Cornwall.·        
The River Dart – Untwists its way down from
Dartmoor to Dartmouth on the South coast of Devon.·        
The River Otter – Sourced in the county of Somerset
near Otterford then flows south for 32 km through East Devon to the English
Channel 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 on
the central northern flanks of Dartmoor across north Devon to Barnstaple.Habitat
RequirementsOtters are solitary and territorial
and are regularly  found next to flowing bodies of water. Otters mostly live along rivers but
have 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 as
lengths of river bank or coast. The sizes of individual territories depend on
the 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 capacity
therefore competition for
new territories is high. Territorial behaviour in otters aids in
controlling the population
density by spacing out individuals. It is also a way of avoiding
over-exploitation of food resources.Feeding
are nocturnal and not very active during the day. They
spend the majority of their time foraging for food, patrolling their
territories and travelling to new locations. They are active and opportunistic hunters,
searching and exploring weed
beds and tree roots along the water’s edge, preying on the easiest
catch or the most abundant. When otters feed they eat
and move on. Their foraging behaviours prevent overfishing and overcrowding
along the stretch of the river.  Otters primarily feed upon fish but
are known to consume a variety of crustaceans, molluscs, frogs, birds and even
small mammals. Their diet varies on the location and time of year due to
resource availability. (In addition Otters undergo  seasonal movements  towards headwaters and upland marshes, taking
advantage of food resources  available to
hunt (Spawning frogs, salmon and sea-trout). Otters that hunt closer to the sea
often forage for bottom dwelling fish such as flounder and Pollack but they
also hunt crabs.