Exmoor's Otter Resurgence
by Michelle Werrett
For otters, simply trying to see them is an inappropriate, a too human approach. To trace the movements of otters it is necessary to revert to more primeval methods. They must be tracked by their spoor: by wading thigh deep in a fast-flowing river or creeping, bent double, under a low-arched bridge to reach a mid-stream rock they are known to favour. Signs of their passing may be ‘padding’, or footprints, left in the silt at the water’s edge, and ‘spraint’, or droppings, deposited on a rock. But the most evocative, most affirming evidence of an otter’s presence is its smell: a warm, sweet, wild, musky odour of water weed, fish and the eternal, untameable current.
Otters are normally solitary animals, except for breeding. Constantly travelling along the rivers they employ a system of scent marking to leave messages for each other. Spraints are deposited in prominent positions that would be difficult for another otter to miss: a large rock in the middle of the river or on the inside of a bend perhaps, or a ledge under a bridge. Since otters work by scent, rather than sight, sprainting sites are not always those that look most obvious. Consideration must be given to the prevailing wind and a site will be chosen so that the wind will take the scent right across a bend in the river. If there is no convenient high spot just where an otter wants one he will sometimes build one himself, scraping up gravel or grass or whatever he can find into a little mound and depositing a spraint on top: a process, and structure, known as ‘castling’. Once the otter’s reasons for the positioning of spraints are understood they are quite easy to find. When fresh, spraints are dark and oily with the crunchy texture of fish bones and scales. Older spraints tend to dry out and fade, but the speed with which they do changes with the weather so it can be difficult to estimate age. Finding a fresh spraint with the evocative musk that was definitely not there yesterday, so confirming the presence of an otter overnight, can be strangely exciting.
The Somerset Otter Group conducts a co-ordinated annual two-day event where all the county’s rivers are checked simultaneously over a weekend. Any sign of an otter found on day two and known not to have been there on day one definitely confirms the presence of an otter on that stretch of river overnight. This year, for the first time, the survey was extended to cover the whole of Exmoor National Park and, where river catchments cross the boundary, just beyond.
All the major rivers and many of the smaller streams on Exmoor were covered and the survey was sufficiently thorough for it to be unlikely that any otter could have been missed. Indeed, there would not have been space for many more otter territories on the moor. In total 189 sites were checked on Exmoor, of which 151 or 81% had some evidence of an otter. 44, or 23%, produced a positive result on day two and a further 10 had fresh evidence on day one but did not quite make the day two ‘hit’. There were just seven totally blank stretches of river. Some of these were minor, shallow streams on the high moorland, and others small, short streams running into the sea on the North coast which may be just too small to provide sufficient territory for an otter. Other blank patches are known to be due to bitches with young cubs restricting their travels to a small part of their usual range. However, the really exciting discovery was to find that otters are using territories high up on the moor near the headwaters of the main rivers where it might be expected that the supply of fish would be poor. They must be Exmoor residents since it is known that there are other otters with territories below them which would prevent them going downstream. This is the case on the Bray, the Mole, the Barle and the Exe. When the survey results are mapped a little knowledge and judgement is applied to estimate the number of ranges, and therefore the minimum number of adult otters represented. This was adjudicated to a maximum of 26 and a minimum of 23. In other words, there are at the very least 23 otters living on Exmoor!
An otter’s ability to melt invisibly into a relatively small stream belies its size. A mature dog otter might weigh 11kg and measure 120cm in length. A bitch is a little smaller but they do need to be large, powerful animals to make their living in our strongly-flowing rivers. Since their habitat is linear they must be fit to travel considerable distances and to catch fish in ever changing, sometimes hostile conditions. The length of river an otter uses is influenced by a number of factors. The quality of the river is obviously important, and if there are plentiful fish and ample cover an otter will not have to travel so far to meet his needs as on a river where those resources are scarce. Another consideration is the presence of other otters, either pressuring the boundaries of a territory or sharing the finite resources within it. The number of otters a river can support is therefore limited.
It is encouraging to find such a plentiful number of otters on Exmoor and in the surrounding countryside and is testimony to the quality and condition of the rivers. However, it was not always so. Back in the 1960s and 1970s numbers plummeted alarmingly and otters came perilously close to extinction. The removal of certain toxic chemicals from industrial and agricultural use has been the main driver in cleaning up our river systems and restoring their population. Information about otter numbers from the more distant past is to be found in the records of the old otter hunters. When they visited the Exmoor rivers in the nineteenth century the numbers of otters found were very similar to the numbers here today. It is fantastic to think that otter numbers are now back to full capacity. Yet complacency must never allow another population crash from which, next time, they may not recover and it is vital that the surveys continue so that any such disaster can be noticed and acted upon promptly.
Lithe and sinuous as a moorland stream, moving with the fluidity of the current; brown as the dark pools, quick as the chuckling riffles, otters are as much a part of a river as the trout and the dappled pebbles. Though we may seldom see one it is good to know they are there.
Further details about the Somerset Otter Group and the full survey results can be found through the Somerset Wildlife Trust website at www.somersetwildlife.org
