Otters by Margaret Holland
With more and more otters to be found across Suffolk, the chances of spotting one have never been better. But although they have been returning to traditional lowland haunts and even establishing themselves in more urban environments, otters remain vulnerable.
Pollutants, destruction of river bank habitat and deaths on the county's roads are all factors that threaten the region's otters. However, sensitive management and building logpile holts can help mitigate these factors.
Habitat and lifestyle
Otters live along rivers, lakes and occasionally estuaries and coasts. They can use a variety of habitats found within the river floodplain such as reed beds, fen and woodland. Coast-living otters need fresh water to clean salt from their fur; otherwise they will lose the ability to keep themselves warm. Otters are generally nocturnal and sightings are rare.
Otters feed mainly on fish. Slow-moving coarse fish are generally eaten as they are easier to catch, but otters will eat a variety of fish depending on what is available. In East Anglia, otters especially favour eels and in the spring, frogs are important food items. Otters occasionally take water birds such as coots, moorhens and ducks.
Recognising otters
Otters have brown fur on their back and a pale underside, long slender bodies with a tapered thick tail and webbed feet with five toes. Otters are sometimes confused with the feral American mink, although mink are much smaller (cat size or smaller) and swim more buoyantly, with their back well above the water surface.
Otters deposit faeces, known as spraints, which have a characteristic sweetly fishy smell, in prominent places within their ranges. These probably serve to mark an otter’s range and help neighbouring animals keep in social contact with one another. Mink droppings are usually twisted in shape and smell very unpleasant – a sure test if you are brave enough!
Otter footprints have five toes and are about 50 mm across – compared to dog or fox footprints, which only have four toes and are generally smaller. Mink also have five toes but are much smaller.
Females breed when they are about two years old. Mating can take place at anytime of year with two or three cubs born in a den, called a holt. These can be within tree root systems, a hole in a bank or under a pile of rocks. About ten weeks elapse before the cubs venture out of the holt with their mother, who raises the cubs without help from the male. Initially females catch food for their cubs, which remain with her for about six months to a year. Otters can live to be ten years old, although few survive more than five years.
Why does the otter need help
In the late 1950s and early 1960s otters underwent a sudden and catastrophic decline throughout much of Britain and Europe. The cause was probably the combined effects of pollution and habitat destruction, particularly the drainage of wet areas. Persistent pesticides, which otters accumulate in their bodies because they are at the top of the food chain, were in widespread use at the time. Otters have returned to our rivers and are now widespread in Suffolk. Populations are recovering, but the otter is still vulnerable.
Threats include:
• A lack of suitable habitat along rivers to provide safe and secure areas for otters
• Poor water quality and pollution means insufficient food for otters
• Roads are a major threat to expanding otter populations. Otters are killed as they move out of existing strongholds and re-colonise their old haunts
• Other incidental deaths can occur in nets to catch eels, known as fyke nets
• Disturbance from increased use of waterways for recreation is a growing problem
Legal protection
Otters are strictly protected by the Wildlife and Countryside Act (1981) under which it is illegal to kill or remove an otter from the wildlife without a licence; damage or obstruct a holt; or disturb an otter in its resting place. A licence may be required to carry out management works that may disturb a resting otter.
Conservation and sensitive management
Otters require clean rivers with an abundant, varied supply of food and plenty of bankside vegetation offering secluded sites for their holts. Some are known to use 40km or more of river habitat. Riversides often lack the appropriate cover for otters to lie up during the day. Such areas can be made more attractive to otters by establishing ‘otter havens’, which may include planting bankside trees, leaving areas as undisturbed scrub and leaving uncultivated buffer zones along watercourses and managing riverside land sympathetically. Wet grassland, fen, reedbeds and their associated dyke networks are also important habitats for otters.
Logpile holts
Surveys have shown that log pile holts are a quick and effective way of providing immediate resting sites for otters. They also provide places of shelter for other animals. Log pile holts are usually more cost effective than other artificial holts.
Consent will be needed from the Environment Agency before any work can take place so it is advisable that they are contacted early on in the process. The Water for Wildlife Project Officer may be able to provide additional advice, visit the site and also help decide on a location as well as advise on an after care and monitoring programme. In some instances fencing and tree planting will be necessary - grant aid is often available for this work.
Requirements
Time (for 5 - 10 people)
• Approximately half a day for chainsaw work (only to be undertaken by a qualified chainsaw operator), trimming poles and brashing
• Approximately half a day for holt construction with pre-cut materials
Tools
• Chainsaw, bowsaw, billhooks, scythe, heavy duty gloves. If the area is liable to flooding then sheep or wire netting, wooden stakes and a mallet will be necessary
Location
• Build the log pile holt as near to the water's edge as possible and where otters can climb the bank
• As long as the site has minimal disturbance from humans and particularly dogs, the log pile holt can be built anywhere along rivers, streams, lakes and ponds, in meanders, field corners, riverside woodlands, islands and stream confluences
• If possible, fence off the patch of land particularly if livestock are present, and either plant with species typical of the locality, or leave it to develop scrub cover naturally. A large area is not necessarily required
Suggested spacing for tree planting
• Plant blackthorn or hawthorn whips at 20cm intervals adjacent to the holt, and alder, ash or willow whips at two to three metre intervals on the periphery of the area
Timber requirements
• Timber can be used from fallen trees, and poles and brashing from a dense hedgeline. Products from woodland or general management work can also be used. Any species can be used, but hardwoods tend to decompose less easily than softwoods and therefore the holt will last longer
• 12 -15 Logs - ideally these should be up to 1m long and 30 - 40cm in diameter
• 50 - 65 Poles - use stout fairly straight tree branches of 3-15 cm in diameter and cut to lengths of 2-3m. Shorter poles can be used to infill gaps
• Brashings - use large quantities of small branches (trimmings from the poles above), hedge brashings or conifer plantation trimmings
Construction
The aim is to try and provide a number of interconnecting chambers which are dark and reasonably dry. The shape of the holt is determined by the location and can be rectangular, square or round. Construction is in three stages forming three layers:
STAGE 1:
Place logs to form chambers of about 1 metre square. Two to eight chambers should be included. Leave gaps of about 15-20cm round as entrances. One or two entrances should be immediately on the river or water's edge, with other entrances onto the land.
STAGE 2:
Use poles across the logs and chambers to form the roof. Small pieces of wood can be used to fill the gaps to make the chambers darker and more water resistant.
STAGE 3:
Pile the brashings on top of the structure to completely hide the logs and poles and make the chambers dry and
dark. It is best to break or saw branches so that they lay flat and pack down. Lay branches stems inwards, with
smaller branches and fronds overlapping logs and poles to form an outer fringe.
If the site is liable to flooding, stretch sheep netting over the brashings and stake netting down on both sides of the
holt. Wooden stakes can be made on site. Place more brashings on tope to hide the wire.