SUMMARY OF RESULTS.
This year’s survey took place at the end of a long period of very low water. The last spell of significant rain ended on 5th January, more than 3 months before the survey on 14th & 15th April. Obviously this affected the amount of otter evidence. It increased the number of old spraints found on the first day, but made useful mud for padding hard to find. However, I think it also altered the otters’ behaviour, and made them even more elusive. They were not all in their usual haunts. The number of ‘hits‘ was below average, 76 against an average of 90, and the number of ‘near misses’, that is, otters present on day 1 but not discovered on day 2, was up, 26 against 19. In other words, we knew there were otters about, but more of them than usual evaded the overnight scrutiny
Several people found their otters high up in minor tributaries, which is what one expects in summer which is more usually the time when the rivers are low, so that may account for their being harder to find this time. One interesting result was the otter which avoided the sprainting stone and the remote camera trap, but was spotted nearby, so lucky to get included in the results.
You looked at 127 patches, a total of 519 sites, of which 331 (64%) were positive; the average for the last ten years is 71%. Part of the reason for this lower percentage was that no fewer than 15 patches of the 127 had total blanks, much the highest/worst result for this, (average 8). You definitely found 55 otters, and there were 6 others we could add in, under the heading of ‘Reasonable Suspicion’; that is otters we know about from other sources such as fishermen, but which were missed by the survey. As always there were a few places where we could not find a trained volunteer for the weekend in question. This is bound to happen, as our helpers have other commitments, but if the system of early warning of absence is operated we frequently manage to get cover. We are trying to put a better system in place for planning the distribution of patches, but basically it all depends on you the surveyors keeping in touch with HQ. That gives a minimum total of 61 otters we definitely knew to be present, but it would be as valid to interpret the dots on the map a tad more generously. The near misses are often very useful in helping the adjudicator to decide whether there were two otters present, or one very mobile one. Nobody can quibble with the score of 61, but more probably the true final total was 67. Our recent average result is 66. Strictly speaking, this is a tally of occupied otter ranges located, and a minimal count of individual animals, as families are not counted, only one per area, which is all we can be absolutely sure of, on the basis of signs, even if we happen by luck to see more, a bitch with cubs for example.
These were distributed thus: Exmoor in Som. 7; N Coast Strs. 11 (or12); Tone 12 (14); S Coast in Som 3 (4); Parrett 13 (14); Cary 0; Brue 10; N Axe 2(3); Frome (3).
This year we again surveyed the whole of the Exmoor National Park, and came up with 21 otters, which is consistent with what we found before.
Our first survey of the whole national park was in 2009, when we looked at 187 sites on Exmoor, 151 of which (81%) had signs of an otter. 44 hits and 8 near misses (29%) gave an adjudicated score of 23 otters, possibly 26. It slightly depends on where you draw the boundary, as sometimes the hit on an Exmoor NP otter is just over the arbitrary and invisible borderline which designates that area.
The following year, 2010, 205 Exmoor sites gave 161 with evidence (78%). 43 hits and 16 near misses (27%) boiled out to 24 otters. For comparison, in the full survey of the whole county for 2010, 521 sites showed evidence at 380 of them (73%), and we claimed 66 occupied otter ranges, (29%).
We could not produce an ENP result for 2011, as the Devon side did not get its people organised, but the Somerset end of the park seemed to be much as before, and the whole of Somerset came in at 318 positive sites out of 477 (66%), scored as 62 ranges minimum, 69 probable (29%).
This year, 2012, from 174 Exmoor sites, 117 (67%) were positive, resulting in 24 hits, and 9 near misses, giving a minimum total of 21 otters.
What can be inferred from all these numbers? Firstly, we are looking at enough places to give a fair assessment of the otter situation. We get a steady number of negative sites, enough to think that had there been some more otters we might have found signs of them at these vacant places. If we were getting over 90% positive sites, it might suggest we need to look more widely. That our survey effort is adequate is confirmed by the spacings on the maps; although the locations vary from year to year, the distances between otters are consistent. It looks as if, on average, we get hits and near misses, ie fresh evidence, from nearly 30% of the recently occupied area for each otter; the DNA study we did in 2000 indicated that dog otters on the Tone had a range of about 12 kms, and the 2Day Events show that they use about 4 of them in a normal night. This is borne out by what we seem to find by other methods, and what the hunts used to find in the last century.
We have been lucky that the weather has not destroyed any one of our surveys in all the years we have been doing them, but the varied state of the rivers in the periods before we survey them does have a major influence on how much older evidence is still there for us to find on the first day. However it has had no influence on the steadiness and consistency of our results. Our method was sufficiently sensitive to pick up whatever the problem was in the disaster years of 2005 and 2006, when ‘otters located’ dropped to 45, and recorded deaths went up by almost 50%. So it can be relied upon when it shows, as it does, that in the last 5 years we have consistently found between 62 and 65 otters across Somerset. This in turn gives confidence that the result for the Exmoor National Park is reliable, and that there is room on those moorland streams for between 20 and 24 otters .
However, what we cannot tell from these annual glimpses is whether that is the strength of the otter population all year. We always survey at the same time, late April: it may be that there is an influx of otters up onto the moor in the spring to take advantage of the spawning frogs and toads. Nor do we know what sorts of otter are living up there, young, old, single, breeding. Do they live there of choice, or are they forced by the competition for prime territories to inhabit a less than totally desirable area. Does their diet differ from that of ‘more fortunate’ otters that live on richer streams?
There is scope for a major investigation here, but as a preliminary I have checked the deaths roll, for the three relevant catchments, Exe, Taw, and North Coast Streams. The lists go back as far as the 1980’s, when the otter population was much less in numbers than it is now, and presumably also demographically skewed, with probably fewer cubs being born to such bitch otters that were still alive. From the 249 deaths recorded, only 17 were in the ENP. This is probably as much a result of the layout of the roads, as an indication of fewer otters. Also the ENP forms only a small part of these catchments, a vast area in total. Of the 17, 3 were cubs, and 3 sub-adults. 5 of these 6 were on North Coast streams. This indicates that the bitch otters up there do sufficiently well to come into breeding condition. That we have found 3 dead cubs may not necessarily be indication that the streams are inadequate to rear cubs; there are always bound to be some losses in such a stressful nursery as a river.Anyway, 2 of the sub-adults were road deaths, and both occurred on a ridge, at a crossing place between two river systems, which may show that they were successfully reared to dispersal stage. The other 4 were listed as not road related. It is interesting to wonder why we have no evidence of breeding on other moorland streams. Maybe the northern otters are able to supplement their diet from the tidal zone.
As ever with these enigmatic animals, there is so much to wonder about, and our surveys seem to throw up as many doubts as answers. However, they do show that there are still otters about across the county and the national park. For those of us who were interested in otters when they declined, this is a great reassurance.
A chart showing Somerset otters seem to have recovered after the disaster year of 2006, and that their population has plateaued out at a steady level.