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Otter

Background

OtterThe otter Lutra lutra is the largest member of the weasel family (Mustelidae) found in Britain.  Reliant on a diet consisting mainly of fish, otters occupy a range of wetland habitats including rivers, streams, lakes, marshes, ditches and coastal areas.  In freshwater habitats, otters are largely (but not exclusively) nocturnal.

A male otter may use 20-40km of river, tributary streams and associated ponds and wetlands as its ‘home range’ (undefended territory). Females have much smaller ranges of 10-20km.

Within its home range an otter will use many resting-places, which may be used regularly or only occasionally. These may be holes amongst riverside tree roots, outlying badger setts, or enlarged rabbit burrows. Otters will also rest above ground in patches of scrub and in undisturbed areas of tall grass or other similar tall vegetation.

Otters can breed at any time of year. A female otter gives birth to 1 to 3 (occasionally up to 5) cubs, after a pregnancy lasting 63 days. The cubs are born blind and helpless with a covering of fine grey fur, in a secluded ‘natal holt’ (breeding den), which is often away from the main river in an undisturbed location. The mother may move the cubs to another holt if they are disturbed or she is concerned about their safety.

The cubs start venturing from the holt after about 2 months and are gradually weaned and taught to swim and hunt by the mother. After about 12 months, when the cubs can fend for themselves, they leave their mother to find their own stretch of river.

Conservation status

Otter populations throughout Western Europe declined over the 20th century, with the decline in the UK attributed to the introduction of cyclodiene pesticides in the mid-1950s and their subsequent bioaccumulation in the aquatic food chain. Legislation restricting or banning the use of certain pesticides coupled with improvements in water quality and re-introductions have led to an increase in otter abundance and range.

Legislation

Otters are protected by the EC Habitats Directive, which is transposed into domestic law through the Conservation (Natural Habitats, &c.) Regulations 1994. Under the “Habitats Regulations”, otters are classed as “European Protected Species” and therefore given the highest level of species protection.  In summary, it is illegal to:

  • deliberately or recklessly kill, injure or take (capture) an otter
  • deliberately or recklessly disturb or harass an otter
  • damage, destroy or obstruct access to a breeding site or resting place of an otter (i.e an otter shelter)

Thus, otter shelters are legally protected whether or not an otter is present.

The otter is also a UK BAP Priority Species and has been adopted as a Species of Principal Importance in England under Section 41 of the NERC Act 2006 (Section 42 in Wales) and the Conservation (Scotland) Act in Scotland.

Licensing

A survey licence is required for surveys using invasive techniques and equipment such as endoscopes to view inside holts. Licences for use of camera traps at a resting site may be required if this would result in disturbance.  Licences to permit actions that would otherwise be illegal under the relevant legislation are issued by Natural England, the Countryside Council for Wales, Scottish Natural Heritage, the Northern Ireland Environment Agency or the National Parks and Wildlife Service (Republic of Ireland), depending on site location.

Survey

As otters are highly mobile and wide ranging, assessment of development impact on otters may need to take account of watercourses beyond the immediate development footprint.

An otter survey would typically involve a systematic search for evidence of otter presence along a watercourse. The most common recorded evidence of otter presence along a watercourse would be presence of otter spraints (faeces).  Spraints have a very characteristic “sweet” odour and are deposited in prominent locations close to the watercourse on tree roots, stones, boulders, tussocks of vegetation or man made structures such as bridge footings.  Spraints vary in size and form, and can range from green or black mucus-like deposits that lack any particualr form, to stools containing the remains of prey items such as fish or amphibian bones and/or the exoskeletal remains of crustaceans.

Otter footprints are also very characteristic but are often more difficult to find as they are easily eroded or not present due to an absence of suitable soft substrates to search.

Otter spraints on a boulder - Aberdeen

Otter spraint with signal crayfish antennae - River Thames, Oxford

Otter spraint without prey remains - River Thames, Oxford

 

Applied Ecology Ltd has extensive experience of conducting otter survey across the UK and has used camera traps to help verify the status and use of potential shelters by otter.

 

 

Mitigation

Planning permission could be refused for sites where otters are present unless it can be demonstrated that otters will be protected during the development process and that disturbance will be kept to an acceptable minimum. In some cases mitigation may be as simple as modifying construction site practice in order to minimise disturbance to otters and otter habitat.

If it is impossible to avoid general disturbance to otters, or the destruction of their shelters and habitat, then appropriate mitigation and compensation measures should be implemented under the auspices of an EPS licence. Where the destruction of a holt has to take place, suitable compensation would be the provision of one or more artificial holts. These can be constructed to several different specifications according to the local circumstances, and in riverine and other freshwater habitats, both log pile holts and pipe and chamber holts are commonly constructed.

New roads can be a particular problem and may lead to significant otter mortality when rivers are in spate and otters have to leave the watercourse and cross the road becasue they cannot navigate below a road bridge crossing due to flood waters.  Ideally new river crossings should be designed that retain a wide strip of accessible riparian habitat on either side which can accommodate spates, thereby providing a safe route under the bridge at all times.  If this is not possible, the use of wet culverts and dry tunnels can be employed. In wet culverts, a ledge 45-60cm wide, 15cm above the highest flood level giving a minimum headroom of 60cm is necessary to enable otters to avoid the water and use the structure successfully.  The ledge must be provided with ramps at each end such that it is accessible both from the water and the bank.  Culverts and tunnels both require suitable fencing to guide otters towards them, if they are to be effective.

See Survey Calendar for survey timings.

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