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Ecology of otters in Northern Scotland IV. A model scheme for otter Lutra lutra L. conservation in a freshwater system in aberdeenshire
Biological Conservation 20 (1981) 123 132
ECOLOGY OF OTTERS IN NORTHERN SCOTLAND IV. A MODEL SCHEME FOR OTTER L U T R A L U T R A L. CONSERVATION IN A FRESHWATER SYSTEM IN ABERDEENSHIRE
DAVID JENKINS
Institute of Terrestrial Ecology, Brathens, Banehory, Scotland
ABSTRACT
Habitatsjor inclusion within otter havens are illustratedJi'om a case-history study on the middle part of the Aberdeenshire Rivet" Dee. The environment is divided into breeding and rearing areas and plaees f o r non-breeding otters. One good location f o r a haven incorporating all three habitats includes 12 13 km of river and two nearhv Ioehs. In this area, part of the river bank is inaccessible, and there are secluded islands and deep woods. Havens should include tiny tributaries leading to shelter where otters are likeO' to have their young. An otter haven in mid-Deeside planned to incorporate all these habitats may be regarded as a model f o r conservation that could be f})llowed in other similar environments elsewhere.
INTRODUCTION
Recently it has been proposed that otters Lutra lutra L. should be conserved by the designation of 'otter havens' (Joint Otter Group, 1977; Wayre, 1979). These are mainly envisaged as small (ca. 0-5-1.0 km) stretches of river bank with natural vegetation where disturbance to otters is minimised. This proposal has been widely applied in England, including the registration of supposed suitable habitat, but there have been few studies of the otter's real habitat requirements throughout its life history. Until such studies are completed in a range of environments it is impossible to provide an assured basis for policies of conservation of otter habitat. However, as a result of research in Aberdeenshire in 1974-79 it is now possible to make recommendations about some features to be incorporated in otter havens there. This research is described by Jenkins (1980), Jenkins & Burrows (1980), and Jenkins & Harper (1980). 123 Biol. Conserv. 0006-3207/81/0020-0123/$02.50 ((~ Applied Science Publishers Ltd, England, 1981 Printed in Great Britain
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DAVID JENKINS
The study area was between Aboyne village and Polhollick bridge in the middle section of the wide valley of the River Dee (Fig. I). It included 26 km of the main river, with some secluded banks and quiet tributaries of varying size, and in particular two lochs,(Kinord (82 ha) and Davan (42 ha)), known as the Dinnet lochs, with plentiful food, extensive reed-beds and small tributaries running through woods. Arable land occupied only a small proportion of the river banks. Part of the area was on the Muir of Dinnet National Nature Reserve. All was on private ground with gamekeepers, and access by the public was generally found at only a few places. Dogs were required to be kept under control throughout the area. No otter was known to have been killed deliberately; on the contrary the fishermen and gamekeepers were all interested in conserving these animals. Spraints (faeces) and footprints were used as indices of use of the habitat and as evidence of the presence of small otters. Analysing spraints also gave a good idea of the foods the otters had eaten. Otters eat a great variety of foods and no distinction has so far been made in the literature between the nutritive needs of otters at different stages of their life cycle. In the Deeside study, spraints collected from places where there were young otters mostly contained the remains of eels Anguilla anguilla L. and salmonids which are highly nutritious. At the Dinnet lochs, eels were much the commonest food at all seasons. In the River Dee, eels predominated as food in summer and small salmonids in winter. Salmonids were also important foods in moorland tributaries, which were used by otters chiefly in the autumn when the fish were migrating upstream to spawn. Although eels and salmonids were the commonest food items, a wide range of prey was recorded. Otter spraints were found throughout the study area, but at greatly varying densities. They were concentrated near bridges, on flat piers and breakwaters running out into the river, on big boulders in the river, on hummocks on otter runs across bends in the river, at resting places, and on characteristic riverside tussocks, stones, and logs and tree roots used for marking purposes. Most spraints were found in places where the river banks had trees (see below). Few spraints were found on long stretches of river with unvegetated banks, nor were any rearing places near villages. Resting places used by otters were found in a variety of places, including cavities within and under trees on river banks, holes under boulders, in scree slopes and sand banks, and under birch (Betula sp.) and other tree roots up to 100-200 m away from water. At least one couch was made and used in a reed-bed.
LOCATION AND CHARACTERISTICS OF DIFFERENT HABITATS
The habitat requirements of otters are considered here in three main classes: breeding places, rearing places, and habitats for non-breeders. Breeding places are the holts in which young are born and their immediate surrounds, rearing places are
ECOLOGY
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where the young are brought at 3-4 months old when they become mobile and where they stay until independence, if they survive, and habitats for non-breeders are where the rest of the otter population is found.
Breeding places Although searches of the river banks and loch edges revealed m a n y temporary resting places, no breeding holts were found, it is unlikely that breeding holts would have been missed if they had entrances to the water or close to it. In the latter case the access would have been obvious in muddy places or in snow. Erlinge (1967) also found that holts with underwater entrances were u n c o m m o n in Sweden. Moreover, footprints of otters less than three months old were seldom recorded at either the River Dee or at the lochs (Jenkins, 1980). Three breeding holts were studied elsewhere by a member of the otter research team (R. J. Harper, pers. comm.). One was under the root system of a very large alder A lnus glutinosa tree about 7 km up a shallow tributary, the Humbie Water, of the River Tyne in East Lothian. The other two were in marshy woodland well away (c. 75 m and c. 800 m) from the main river, but close to a very small streamlet of less than 1 m width, in Inverness-shire and Berwickshire. The Humbie Water was not known to flood to the same extent as the tributaries of the River Dee. Captain J Bell-Irving, Master of the Dumfries-shire otter hounds, confirms (pets. comm.) that otters seldom have their young in holes on banks of rivers which are subject to sudden spates. The exceptions are very high banks where holts cannot be reached by floods. At such places the holts have access at various levels, and all those known to Bell-Irving had holes going well out into a field or wood, mostly at the level with least risk of flooding. Very small 2-3 months old otters were found only twice during the study, both times well up tributaries. One was seen alive in March 1977, about 4 k m up the Water of Tanar (Fig. 1), and the other was shot by a gamekeeper in November 1978 in mistake for a mink Mustela vison Schreber about 3 km up the narrow Ordie burn north of Loch Davan (Fig. 2). From all this it was concluded that otters rarely had young in holes on the banks of the River Dee or the Dinnet lochs, and would not be expected to do so. Most probably, breeding holts were usually located away from the larger waters, perhaps in woods or in quiet places up small tributaries, with the young coming to the big river or lochs when they were mobile and staying near the mouth of the tributary on the main river if the place was suitable.
Rearing places Young otters of 3-4 months of age or older were recorded from sightings and from footprints. While there is little information on very small otters, there was abundant evidence from sightings and footprints around the lochs and the big river of young otters over three months old. Each year, two or more families of otters were reared at the Dinnet lochs. No family was recorded there till the young were 3--4 months old
ECOLOGY OF OTTERS IN SCOTLAND
127
KEY I
Continuousdensewoodland Dsi conJ2~u.ouwood s land. . . . . ly birch
I
.....
Fig. 2. Part of mid-Deeside, showing proposed otter haven. The habitats shown distinguish those within which otters can hide and obtain seclusion from arable and grass fields and moorland with short heather.
and each family r e m a i n e d for u p to seven m o n t h s , or in two cases, up to a b o u t one year. A t the lochs, most spraints were f o u n d in the extensive reed-beds and birch or alder scrub, with over five times as m a n y on average in the g o o d cover as were found on the b a r e r shores o f the same loch. On the River Dee, despite the large variety o f places where spraints were f o u n d , a b o u t 10 15 'j'{,( d a t a in Jenkins & Burrows, 1980) o f the total v a r i a t i o n in s p r a i n t densities c o u l d be a t t r i b u t e d to a positive association with w o o d l a n d cover. F r o m this, it seems clear that the otters preferred stretches o f river or lochs with w o o d s o r r e e d - b e d s which p r o v i d e d g o o d seclusion from people. In the 16 k m stretch o f the River Dee w e s t w a r d s from A b o y n e , o t t e r families were recorded in three localities. These were at W a t e r s i d e , Dinner and C a m b u s O ' M a y (called C a m b u s below) (Fig. 1). In the less well surveyed stretch 16 2 6 k m west o f A b o y n e , the only families detected were at Polhollick in June 1977, and on two d a y s in g o o d cover a b o v e Ballater in A p r i l 1978. This last family m a y have been at C a m b u s previously a n d was not r e c o r d e d at Ballater in the next week. T h e site at W a t e r s i d e was an island with the first g o o d w o o d l a n d cover west o f
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Aboyne. This island was easily accessible at low water, was visited by salmon fishermen from February onwards, and provided security only in early winter when there were few walkers, and before the fishing season opened. Otter families with young about 3-4 months old were recorded in snow in two winters, but not in spring and probably no young stayed or survived to become independent. The next rearing site on the Dee was on wooded islands near the mouth of the tributary draining the Dinnet lochs. The islands were inaccessible to people in winter floods, but some were accessible in summer and autumn when the river was low. Here, signs of young were present throughout the winter but were absent in summer. The site at Cambus (Fig. 1) had a string of wooded islands which were inaccessible except in drought, with on one side a high, steep, impassable wooded bank and a big conifer forest coming to the water's edge and on the other side a long walk over private ground to the nearest road. On the riverside there were cleared stances on the forest edge for fishermen and in some cases these were separated from each other by tongues of forest running to the river's edge. The riverside path linking these stances was then inside the wood so that parts of the river bank remained secluded and undisturbed. Peaks of spraints (see Jenkins & Burrows, 1980) occurred here in February, May, June and August/September in 1977, and in most months in 1978. In February 1977, there were accumulations of spraints at two main sites, including the mouth of the tributary Tullich Burn as well as the wooded area at Cambus. Young were recorded on the Cambus stretch in late winter in both 1976/77 and 1977/78 and in O c t o b e r - N o v e m b e r 1978 when the study ended. At Polhollick also the bank was well-wooded and steep with difficult access. Further upstream, near Abergeldie and Balmoral, where young otters were recorded in 1978, some stretches of the river had good cover from woods and few people, but above Invercauld bridge few signs of otters were found. This suggested that otters seldom used the upper parts of the river. Sites at Dinnet, Cambus and Polhollick were near the mouths of sizeable tributaries, and there were smaller tributaries at Abergeldie and Balmoral and a very small one at Waterside. However, young otters were not found at the mouth of the tributary Water of Tanar, which had very good cover but which was near Aboyne village, nor at the mouth of the tributary River Muick near Ballater where the cover was extremely poor, nor at the mouth of the tributary River Girnock where cover was good. The mouths of the Girnock and T a n a r were well-used by otters, but not by young during the study; however, from reports by local people, otters were probably reared further up the well-wooded Water of Tanar. The places with most families were the Dinnet lochs area, which had big reed-beds and small secluded tributary streams, and at Cambus with little frequented wooded islands and banks. The importance of secluded reed-beds or woodland cover for otter rearing places seems well established. Summarising, on 16 km of the River Dee in 1976-78 few signs of young otters were found in places devoid of cover. Young were recorded over the shortest period at
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Waterside which was visited regularly by people for much of the year and was quiet only in early winter. Intermediate rearing success was recorded at Dinnet islands, with few people at any season but isolation only inwinter. Here, winter young were recorded over long periods, while young found in June disappeared. The best place was the quiet, wooded stretch at Cambus where there were few people at any time.
Habitats q[non-breeding otters The only firm evidence on the movements of a non-breeding otter comes from the faeces of a single male marked with radio-active zinc in October 1978 when 4--5 months old. It stayed with another otter, probably its mother, at the Dinnet lochs and their tributaries until February and then commuted regularly between the lochs and about 2 km on the Cambus stretch of the River Dee. It gradually increased this range, to about 8 k m at 9 months. When 10 months old, it used at least 16km of river, sometimes travelling 17-25 km in a night. It disappeared when about 11 12 months old, having covered at least 68 km of the River Dee altogether. It is unknown when it left its mother. Spraints and footprints of full-grown otters were regularly recorded on the banks of the River Dee near the mouths of both the Tanar and the Girnock, suggesting that at this time these wooded stretches of river and adjacent parts of the tributaries were used by otters without young. Possibly families were there at other times. Spraints were also found at remote lochs on high ground which were frozen for much of the year and where there were no signs of young; these lochs and moorland streams may have been mainly frequented by non-breeding otters. A non-pregnant female otter was run over by traffic in the middle of Aboyne village. The inference is that nonbreeding otters use habitats that are unsuitable for breeding but may sometimes temporarily occupy breeding habitats in the absence of young. Otters seem normally to be solitary (except in family parties) and there was no evidence of an accumulation of non-breeders at the Dinnet lochs when there were few or no families; on the contrary, when there were few or no families, no extra single animals were seen. It is this that gave rise to the idea that these lochs should be regarded specifically as rearing areas rather than as generalized otter habitat.
MAIN F A C T O R S A F F E C T I N G H A B I T A T S
On long stretches of the River Dee and some of its tributaries the riverside fringe of trees has been removed in order to improve access for fishing and to make casting easier. Formerly, using a bushman saw, only single branches of riverside trees were removed to aid casting. Now, with a power saw, it is all too easy to take down the whole tree. On stretches where the trees have been removed, the footpath runs close beside the river. In such places otter spraints are seldom found. In many places the felling of trees and bushes is associated with domestic animals grazing to the water's
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edge. On both the rivers and on the banks of the Dinner lochs where trees are sparse there are also few signs of otters. Pollution is not significant in the middle reaches of the Aberdeenshire River Dee. However, more nitrates are entering one of the Dinnet lochs than the other, and this enhanced inflow may lead to eutrophication and greater growth ofmacrophytes. At the moment this is not giving cause for concern but monitoring water quality is an obvious requirement for otter conservation. In the relatively unpolluted habitats on the edge of the Highlands the removal of bankside vegetation and increased disturbance are probably the greatest hazards affecting otters. Disturbance arises partly from fishermen and walkers, especially people with uncontrolled dogs, but a new hazard in the middle stretches of the River Dee may be arising from canoeing. Places inaccessible to fishermen and walkers may be readily reached by people in canoes. Sites near bridges, which provide access to both banks, may be particularly vulnerable to such disturbance.
P R O P O S A L S F O R C O N S E R V A T I O N OF OTTERS IN M1D-DEESIDE
Three different habitat requirements for otters are identified in this paper: breeding habitats, rearing habitats, and the habitats used by non-breeders. Few breeding holts have been described. In Deeside, they are probably mostly in steep banks near streams, in cover beside small drains, or well up tributaries where the risk from flooding is small. Much more is known about rearing areas. These are quiet lochs or wooded stretches in the middle reaches of large rivers, often near the mouths of tributaries, where there is plentiful, nutritious food. Families of otters probably regularly move between the rich habitats in lochs and rivers. To conserve otters adequately, both breeding and rearing places should be included within a protected area. Protecting only the place where young are reared may not be enough. Probably the whole system of the River Dee is used by sub-adults and other nonbreeders, ranging from the upper stretches of the river (e.g. above Invercauld), including moorland tributaries and lochs at high altitude, to the river and harbour in Aberdeen city where otters are reported occasionally. So little is known about the requirements of the non-breeding population that it is impossible to make recommendations for conservation of their habitats. However, the movements of the one marked young animal suggest that long stretches of the river need conservation to give protection to individuals that are not attached to particular localities. These animals will include adult females inbetween litters and adult males mated to more than one female. In this case the following features would require to be included within the protected haven. It is suggested that this is located between the Dinner and Tullich burns (Fig. 2) to include known good rearing places at Dinnet lochs and on the river.
E C O L O G Y OF OTTERS 1N S C O T L A N D
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Features are described under the life-cycle habitats described above, but obviously some may be used at more than one stage of the otter breeding cycle. (a) Breeding habitat: all tributaries, however tiny, and associated woodland and other nearby cover such as scree slopes within 500 m of the tributary or river banks. and the streams, marshes and woodland associated with the Muir of Dinnet and Dinnet Oakwood National Nature Reserves, especially the tributaries feeding Loch Davan which are not at present in the Muir of Dinnet National Nature Reserve" (b) Rearing habitat: the Dinnet lochs, the tributary mouths (Dinnet, Pollagach and Tullich burns) and their associated cover, especially about l km up and downstream of the bridges at Dinnet and Cambus, and the marshes and woodland of the existing National Nature Reserves: (c) Habitat for non-breeders: all water courses, including both banks of the River Dee, between Dinnet and Tullich burns. The main management requirement would be to maintain the vegetation as at present. For example, no access or grazing should be allowed on islands, stances for fishermen on wooded banks should continue to be separated by trees, paths should remain inside woods or at least within a bankside fringe of trees and not be on the river banks, riverside forests (and those up tiny tributaries, e.g. at Blelack, well up the Ordie burn) should be felled in small coupes and replanted or regenerated quickly so that some good cover always remains, tree and scrub cover should be maintained or improved up all tributaries, in addition, no snares (ostensibly for rabbits Or)'clolagus cuniculus or foxes Vulpes vulpes, but which might catch otters) should be set within about 500m of river or loch, and access by the public, including canoeing, should be restricted as at present, mainly by making it difficult to walk along parts of the river banks or gain access to them. Finally, all kinds of pollution in tributaries should be prevented, and water quality should be monitored. Monitoring the behaviour of the otters in the haven is also desirable, and existing breeding dens should be found (perhaps by seeking the help of professional otter hunters) so that dens can be protected: but providing artificial dens for breeding at the water's edge would probably be a wasted effort because the otters would not be expected to use them. This protected area would thereby probably include natural breeding areas and habitat for the non-breeding section of the otter population as well as rearing areas, and would provide a model for the creation o f ' o t t e r havens' in environments such as this. The total area involved (shown in Fig. 2) would be 12 13 km of river, say 3 5 km of each of the four main tributaries (Dinnet, Pollagach. Tullich and Ordie) and shorter distances of several tiny streams, plus the two lochs ( 124 ha). This large area might cover the needs of only about 2-4 families in any one year. Habitat protection for one rearing area is assured within the National Nature Reserves of Muir of Dinnet and Dinner Oakwood. Elsewhere it is likely that present policies of the private landowners would largely prove effective in maintaining the habitat.
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Nonetheless, some f o r m a l r e c o g n i t i o n o f the status o f the area w o u l d be desirable, in o r d e r to ensure that at least some breeding places are preserved and some h a b i t a t for n o n - b r e e d i n g otters, a n d to agree a policy for felling c o m m e r c i a l w o o d l a n d . This p e r h a p s could best be achieved by setting up an otter haven to cover the r e m a i n d e r o f the critical habitats. Ideally there should be several otter havens o f v a r y i n g lengths a l o n g the river, p a r t i c u l a r l y in the w o o d e d middle stretches where it m a y be m o r e p r a c t i c a b l e to establish t h e m t h a n further d o w n where pressure from agriculture m a y be c o n s i d e r a b l e .
ACKNOWLEDGEMENTS J o h n Bell-Irving, M i c h a e l Harris, E l i z a b e t h Lowe and p a r t i c u l a r l y J o h n F o r s t e r c o m m e n t e d constructively on drafts. R o s e m a r y H a r p e r drew the figures, including a c o m p l e t e l y new m a p o f M u i r o f D i n n e t N N R . M a r t y n G o r m a n a n d the Z o o l o g y D e p a r t m e n t at A b e r d e e n U n i v e r s i t y helped greatly with the w o r k with isotopes.
REFERENCES ERLINGE, S. (1967). Home range of the otter Lutra lutra L. in Southern Sweden. Oikos, 18, 186--209.
ERLINGE, S. (1968). Territoriality of the otter Lutra lutra L. Oikos, 19, 81 98. JENKINS, D. (1980). Ecology of otters in northern Scotland, I. Otter (Lutra lutra L.) breeding and dispersion in mid-Deeside, Aberdeenshire in 1974-9. J. Anim. Ecol., 49, 713 35. JENK1NS,D. & BURROWS,G. O. (1980). Ecology of otters in northern Scotland, III. The use of faeces as indicators of otter (Lutra lutra L.) density and distribution. J. Anon. Ecol., 49, 755-74. JENKINS,D. & HARPER,R. J. (1980). Ecology of otters in northern Scotland, I1. Analyses of otter (Lutra lutra L.) and mink (Mustela vison Schreber) faeces from Deeside, NE Scotland in 1977-8. J. Anita. Ecol., 49, 737 54. JOINT OTTER GROUP (1977). Otters 1977: First Report. London, Nature Conservancy Council; Nettleham, Society for the Promotion of Nature Conservation. WAYRE, P. (1979). Otter havens in Norfolk and Suffolk, England. Biol. Conserv., 16, 73-81.
ECOLOGY OF OTTERS IN NORTHERN SCOTLAND IV. A MODEL SCHEME FOR OTTER L U T R A L U T R A L. CONSERVATION IN A FRESHWATER SYSTEM IN ABERDEENSHIRE
DAVID JENKINS
Institute of Terrestrial Ecology, Brathens, Banehory, Scotland
ABSTRACT
Habitatsjor inclusion within otter havens are illustratedJi'om a case-history study on the middle part of the Aberdeenshire Rivet" Dee. The environment is divided into breeding and rearing areas and plaees f o r non-breeding otters. One good location f o r a haven incorporating all three habitats includes 12 13 km of river and two nearhv Ioehs. In this area, part of the river bank is inaccessible, and there are secluded islands and deep woods. Havens should include tiny tributaries leading to shelter where otters are likeO' to have their young. An otter haven in mid-Deeside planned to incorporate all these habitats may be regarded as a model f o r conservation that could be f})llowed in other similar environments elsewhere.
INTRODUCTION
Recently it has been proposed that otters Lutra lutra L. should be conserved by the designation of 'otter havens' (Joint Otter Group, 1977; Wayre, 1979). These are mainly envisaged as small (ca. 0-5-1.0 km) stretches of river bank with natural vegetation where disturbance to otters is minimised. This proposal has been widely applied in England, including the registration of supposed suitable habitat, but there have been few studies of the otter's real habitat requirements throughout its life history. Until such studies are completed in a range of environments it is impossible to provide an assured basis for policies of conservation of otter habitat. However, as a result of research in Aberdeenshire in 1974-79 it is now possible to make recommendations about some features to be incorporated in otter havens there. This research is described by Jenkins (1980), Jenkins & Burrows (1980), and Jenkins & Harper (1980). 123 Biol. Conserv. 0006-3207/81/0020-0123/$02.50 ((~ Applied Science Publishers Ltd, England, 1981 Printed in Great Britain
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DAVID JENKINS
The study area was between Aboyne village and Polhollick bridge in the middle section of the wide valley of the River Dee (Fig. I). It included 26 km of the main river, with some secluded banks and quiet tributaries of varying size, and in particular two lochs,(Kinord (82 ha) and Davan (42 ha)), known as the Dinnet lochs, with plentiful food, extensive reed-beds and small tributaries running through woods. Arable land occupied only a small proportion of the river banks. Part of the area was on the Muir of Dinnet National Nature Reserve. All was on private ground with gamekeepers, and access by the public was generally found at only a few places. Dogs were required to be kept under control throughout the area. No otter was known to have been killed deliberately; on the contrary the fishermen and gamekeepers were all interested in conserving these animals. Spraints (faeces) and footprints were used as indices of use of the habitat and as evidence of the presence of small otters. Analysing spraints also gave a good idea of the foods the otters had eaten. Otters eat a great variety of foods and no distinction has so far been made in the literature between the nutritive needs of otters at different stages of their life cycle. In the Deeside study, spraints collected from places where there were young otters mostly contained the remains of eels Anguilla anguilla L. and salmonids which are highly nutritious. At the Dinnet lochs, eels were much the commonest food at all seasons. In the River Dee, eels predominated as food in summer and small salmonids in winter. Salmonids were also important foods in moorland tributaries, which were used by otters chiefly in the autumn when the fish were migrating upstream to spawn. Although eels and salmonids were the commonest food items, a wide range of prey was recorded. Otter spraints were found throughout the study area, but at greatly varying densities. They were concentrated near bridges, on flat piers and breakwaters running out into the river, on big boulders in the river, on hummocks on otter runs across bends in the river, at resting places, and on characteristic riverside tussocks, stones, and logs and tree roots used for marking purposes. Most spraints were found in places where the river banks had trees (see below). Few spraints were found on long stretches of river with unvegetated banks, nor were any rearing places near villages. Resting places used by otters were found in a variety of places, including cavities within and under trees on river banks, holes under boulders, in scree slopes and sand banks, and under birch (Betula sp.) and other tree roots up to 100-200 m away from water. At least one couch was made and used in a reed-bed.
LOCATION AND CHARACTERISTICS OF DIFFERENT HABITATS
The habitat requirements of otters are considered here in three main classes: breeding places, rearing places, and habitats for non-breeders. Breeding places are the holts in which young are born and their immediate surrounds, rearing places are
ECOLOGY
OF
OTTERS
IN
SCOTLAND
125
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where the young are brought at 3-4 months old when they become mobile and where they stay until independence, if they survive, and habitats for non-breeders are where the rest of the otter population is found.
Breeding places Although searches of the river banks and loch edges revealed m a n y temporary resting places, no breeding holts were found, it is unlikely that breeding holts would have been missed if they had entrances to the water or close to it. In the latter case the access would have been obvious in muddy places or in snow. Erlinge (1967) also found that holts with underwater entrances were u n c o m m o n in Sweden. Moreover, footprints of otters less than three months old were seldom recorded at either the River Dee or at the lochs (Jenkins, 1980). Three breeding holts were studied elsewhere by a member of the otter research team (R. J. Harper, pers. comm.). One was under the root system of a very large alder A lnus glutinosa tree about 7 km up a shallow tributary, the Humbie Water, of the River Tyne in East Lothian. The other two were in marshy woodland well away (c. 75 m and c. 800 m) from the main river, but close to a very small streamlet of less than 1 m width, in Inverness-shire and Berwickshire. The Humbie Water was not known to flood to the same extent as the tributaries of the River Dee. Captain J Bell-Irving, Master of the Dumfries-shire otter hounds, confirms (pets. comm.) that otters seldom have their young in holes on banks of rivers which are subject to sudden spates. The exceptions are very high banks where holts cannot be reached by floods. At such places the holts have access at various levels, and all those known to Bell-Irving had holes going well out into a field or wood, mostly at the level with least risk of flooding. Very small 2-3 months old otters were found only twice during the study, both times well up tributaries. One was seen alive in March 1977, about 4 k m up the Water of Tanar (Fig. 1), and the other was shot by a gamekeeper in November 1978 in mistake for a mink Mustela vison Schreber about 3 km up the narrow Ordie burn north of Loch Davan (Fig. 2). From all this it was concluded that otters rarely had young in holes on the banks of the River Dee or the Dinnet lochs, and would not be expected to do so. Most probably, breeding holts were usually located away from the larger waters, perhaps in woods or in quiet places up small tributaries, with the young coming to the big river or lochs when they were mobile and staying near the mouth of the tributary on the main river if the place was suitable.
Rearing places Young otters of 3-4 months of age or older were recorded from sightings and from footprints. While there is little information on very small otters, there was abundant evidence from sightings and footprints around the lochs and the big river of young otters over three months old. Each year, two or more families of otters were reared at the Dinnet lochs. No family was recorded there till the young were 3--4 months old
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KEY I
Continuousdensewoodland Dsi conJ2~u.ouwood s land. . . . . ly birch
I
.....
Fig. 2. Part of mid-Deeside, showing proposed otter haven. The habitats shown distinguish those within which otters can hide and obtain seclusion from arable and grass fields and moorland with short heather.
and each family r e m a i n e d for u p to seven m o n t h s , or in two cases, up to a b o u t one year. A t the lochs, most spraints were f o u n d in the extensive reed-beds and birch or alder scrub, with over five times as m a n y on average in the g o o d cover as were found on the b a r e r shores o f the same loch. On the River Dee, despite the large variety o f places where spraints were f o u n d , a b o u t 10 15 'j'{,( d a t a in Jenkins & Burrows, 1980) o f the total v a r i a t i o n in s p r a i n t densities c o u l d be a t t r i b u t e d to a positive association with w o o d l a n d cover. F r o m this, it seems clear that the otters preferred stretches o f river or lochs with w o o d s o r r e e d - b e d s which p r o v i d e d g o o d seclusion from people. In the 16 k m stretch o f the River Dee w e s t w a r d s from A b o y n e , o t t e r families were recorded in three localities. These were at W a t e r s i d e , Dinner and C a m b u s O ' M a y (called C a m b u s below) (Fig. 1). In the less well surveyed stretch 16 2 6 k m west o f A b o y n e , the only families detected were at Polhollick in June 1977, and on two d a y s in g o o d cover a b o v e Ballater in A p r i l 1978. This last family m a y have been at C a m b u s previously a n d was not r e c o r d e d at Ballater in the next week. T h e site at W a t e r s i d e was an island with the first g o o d w o o d l a n d cover west o f
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Aboyne. This island was easily accessible at low water, was visited by salmon fishermen from February onwards, and provided security only in early winter when there were few walkers, and before the fishing season opened. Otter families with young about 3-4 months old were recorded in snow in two winters, but not in spring and probably no young stayed or survived to become independent. The next rearing site on the Dee was on wooded islands near the mouth of the tributary draining the Dinnet lochs. The islands were inaccessible to people in winter floods, but some were accessible in summer and autumn when the river was low. Here, signs of young were present throughout the winter but were absent in summer. The site at Cambus (Fig. 1) had a string of wooded islands which were inaccessible except in drought, with on one side a high, steep, impassable wooded bank and a big conifer forest coming to the water's edge and on the other side a long walk over private ground to the nearest road. On the riverside there were cleared stances on the forest edge for fishermen and in some cases these were separated from each other by tongues of forest running to the river's edge. The riverside path linking these stances was then inside the wood so that parts of the river bank remained secluded and undisturbed. Peaks of spraints (see Jenkins & Burrows, 1980) occurred here in February, May, June and August/September in 1977, and in most months in 1978. In February 1977, there were accumulations of spraints at two main sites, including the mouth of the tributary Tullich Burn as well as the wooded area at Cambus. Young were recorded on the Cambus stretch in late winter in both 1976/77 and 1977/78 and in O c t o b e r - N o v e m b e r 1978 when the study ended. At Polhollick also the bank was well-wooded and steep with difficult access. Further upstream, near Abergeldie and Balmoral, where young otters were recorded in 1978, some stretches of the river had good cover from woods and few people, but above Invercauld bridge few signs of otters were found. This suggested that otters seldom used the upper parts of the river. Sites at Dinnet, Cambus and Polhollick were near the mouths of sizeable tributaries, and there were smaller tributaries at Abergeldie and Balmoral and a very small one at Waterside. However, young otters were not found at the mouth of the tributary Water of Tanar, which had very good cover but which was near Aboyne village, nor at the mouth of the tributary River Muick near Ballater where the cover was extremely poor, nor at the mouth of the tributary River Girnock where cover was good. The mouths of the Girnock and T a n a r were well-used by otters, but not by young during the study; however, from reports by local people, otters were probably reared further up the well-wooded Water of Tanar. The places with most families were the Dinnet lochs area, which had big reed-beds and small secluded tributary streams, and at Cambus with little frequented wooded islands and banks. The importance of secluded reed-beds or woodland cover for otter rearing places seems well established. Summarising, on 16 km of the River Dee in 1976-78 few signs of young otters were found in places devoid of cover. Young were recorded over the shortest period at
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Waterside which was visited regularly by people for much of the year and was quiet only in early winter. Intermediate rearing success was recorded at Dinnet islands, with few people at any season but isolation only inwinter. Here, winter young were recorded over long periods, while young found in June disappeared. The best place was the quiet, wooded stretch at Cambus where there were few people at any time.
Habitats q[non-breeding otters The only firm evidence on the movements of a non-breeding otter comes from the faeces of a single male marked with radio-active zinc in October 1978 when 4--5 months old. It stayed with another otter, probably its mother, at the Dinnet lochs and their tributaries until February and then commuted regularly between the lochs and about 2 km on the Cambus stretch of the River Dee. It gradually increased this range, to about 8 k m at 9 months. When 10 months old, it used at least 16km of river, sometimes travelling 17-25 km in a night. It disappeared when about 11 12 months old, having covered at least 68 km of the River Dee altogether. It is unknown when it left its mother. Spraints and footprints of full-grown otters were regularly recorded on the banks of the River Dee near the mouths of both the Tanar and the Girnock, suggesting that at this time these wooded stretches of river and adjacent parts of the tributaries were used by otters without young. Possibly families were there at other times. Spraints were also found at remote lochs on high ground which were frozen for much of the year and where there were no signs of young; these lochs and moorland streams may have been mainly frequented by non-breeding otters. A non-pregnant female otter was run over by traffic in the middle of Aboyne village. The inference is that nonbreeding otters use habitats that are unsuitable for breeding but may sometimes temporarily occupy breeding habitats in the absence of young. Otters seem normally to be solitary (except in family parties) and there was no evidence of an accumulation of non-breeders at the Dinnet lochs when there were few or no families; on the contrary, when there were few or no families, no extra single animals were seen. It is this that gave rise to the idea that these lochs should be regarded specifically as rearing areas rather than as generalized otter habitat.
MAIN F A C T O R S A F F E C T I N G H A B I T A T S
On long stretches of the River Dee and some of its tributaries the riverside fringe of trees has been removed in order to improve access for fishing and to make casting easier. Formerly, using a bushman saw, only single branches of riverside trees were removed to aid casting. Now, with a power saw, it is all too easy to take down the whole tree. On stretches where the trees have been removed, the footpath runs close beside the river. In such places otter spraints are seldom found. In many places the felling of trees and bushes is associated with domestic animals grazing to the water's
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edge. On both the rivers and on the banks of the Dinner lochs where trees are sparse there are also few signs of otters. Pollution is not significant in the middle reaches of the Aberdeenshire River Dee. However, more nitrates are entering one of the Dinnet lochs than the other, and this enhanced inflow may lead to eutrophication and greater growth ofmacrophytes. At the moment this is not giving cause for concern but monitoring water quality is an obvious requirement for otter conservation. In the relatively unpolluted habitats on the edge of the Highlands the removal of bankside vegetation and increased disturbance are probably the greatest hazards affecting otters. Disturbance arises partly from fishermen and walkers, especially people with uncontrolled dogs, but a new hazard in the middle stretches of the River Dee may be arising from canoeing. Places inaccessible to fishermen and walkers may be readily reached by people in canoes. Sites near bridges, which provide access to both banks, may be particularly vulnerable to such disturbance.
P R O P O S A L S F O R C O N S E R V A T I O N OF OTTERS IN M1D-DEESIDE
Three different habitat requirements for otters are identified in this paper: breeding habitats, rearing habitats, and the habitats used by non-breeders. Few breeding holts have been described. In Deeside, they are probably mostly in steep banks near streams, in cover beside small drains, or well up tributaries where the risk from flooding is small. Much more is known about rearing areas. These are quiet lochs or wooded stretches in the middle reaches of large rivers, often near the mouths of tributaries, where there is plentiful, nutritious food. Families of otters probably regularly move between the rich habitats in lochs and rivers. To conserve otters adequately, both breeding and rearing places should be included within a protected area. Protecting only the place where young are reared may not be enough. Probably the whole system of the River Dee is used by sub-adults and other nonbreeders, ranging from the upper stretches of the river (e.g. above Invercauld), including moorland tributaries and lochs at high altitude, to the river and harbour in Aberdeen city where otters are reported occasionally. So little is known about the requirements of the non-breeding population that it is impossible to make recommendations for conservation of their habitats. However, the movements of the one marked young animal suggest that long stretches of the river need conservation to give protection to individuals that are not attached to particular localities. These animals will include adult females inbetween litters and adult males mated to more than one female. In this case the following features would require to be included within the protected haven. It is suggested that this is located between the Dinner and Tullich burns (Fig. 2) to include known good rearing places at Dinnet lochs and on the river.
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Features are described under the life-cycle habitats described above, but obviously some may be used at more than one stage of the otter breeding cycle. (a) Breeding habitat: all tributaries, however tiny, and associated woodland and other nearby cover such as scree slopes within 500 m of the tributary or river banks. and the streams, marshes and woodland associated with the Muir of Dinnet and Dinnet Oakwood National Nature Reserves, especially the tributaries feeding Loch Davan which are not at present in the Muir of Dinnet National Nature Reserve" (b) Rearing habitat: the Dinnet lochs, the tributary mouths (Dinnet, Pollagach and Tullich burns) and their associated cover, especially about l km up and downstream of the bridges at Dinnet and Cambus, and the marshes and woodland of the existing National Nature Reserves: (c) Habitat for non-breeders: all water courses, including both banks of the River Dee, between Dinnet and Tullich burns. The main management requirement would be to maintain the vegetation as at present. For example, no access or grazing should be allowed on islands, stances for fishermen on wooded banks should continue to be separated by trees, paths should remain inside woods or at least within a bankside fringe of trees and not be on the river banks, riverside forests (and those up tiny tributaries, e.g. at Blelack, well up the Ordie burn) should be felled in small coupes and replanted or regenerated quickly so that some good cover always remains, tree and scrub cover should be maintained or improved up all tributaries, in addition, no snares (ostensibly for rabbits Or)'clolagus cuniculus or foxes Vulpes vulpes, but which might catch otters) should be set within about 500m of river or loch, and access by the public, including canoeing, should be restricted as at present, mainly by making it difficult to walk along parts of the river banks or gain access to them. Finally, all kinds of pollution in tributaries should be prevented, and water quality should be monitored. Monitoring the behaviour of the otters in the haven is also desirable, and existing breeding dens should be found (perhaps by seeking the help of professional otter hunters) so that dens can be protected: but providing artificial dens for breeding at the water's edge would probably be a wasted effort because the otters would not be expected to use them. This protected area would thereby probably include natural breeding areas and habitat for the non-breeding section of the otter population as well as rearing areas, and would provide a model for the creation o f ' o t t e r havens' in environments such as this. The total area involved (shown in Fig. 2) would be 12 13 km of river, say 3 5 km of each of the four main tributaries (Dinnet, Pollagach. Tullich and Ordie) and shorter distances of several tiny streams, plus the two lochs ( 124 ha). This large area might cover the needs of only about 2-4 families in any one year. Habitat protection for one rearing area is assured within the National Nature Reserves of Muir of Dinnet and Dinner Oakwood. Elsewhere it is likely that present policies of the private landowners would largely prove effective in maintaining the habitat.
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Nonetheless, some f o r m a l r e c o g n i t i o n o f the status o f the area w o u l d be desirable, in o r d e r to ensure that at least some breeding places are preserved and some h a b i t a t for n o n - b r e e d i n g otters, a n d to agree a policy for felling c o m m e r c i a l w o o d l a n d . This p e r h a p s could best be achieved by setting up an otter haven to cover the r e m a i n d e r o f the critical habitats. Ideally there should be several otter havens o f v a r y i n g lengths a l o n g the river, p a r t i c u l a r l y in the w o o d e d middle stretches where it m a y be m o r e p r a c t i c a b l e to establish t h e m t h a n further d o w n where pressure from agriculture m a y be c o n s i d e r a b l e .
ACKNOWLEDGEMENTS J o h n Bell-Irving, M i c h a e l Harris, E l i z a b e t h Lowe and p a r t i c u l a r l y J o h n F o r s t e r c o m m e n t e d constructively on drafts. R o s e m a r y H a r p e r drew the figures, including a c o m p l e t e l y new m a p o f M u i r o f D i n n e t N N R . M a r t y n G o r m a n a n d the Z o o l o g y D e p a r t m e n t at A b e r d e e n U n i v e r s i t y helped greatly with the w o r k with isotopes.
REFERENCES ERLINGE, S. (1967). Home range of the otter Lutra lutra L. in Southern Sweden. Oikos, 18, 186--209.
ERLINGE, S. (1968). Territoriality of the otter Lutra lutra L. Oikos, 19, 81 98. JENKINS, D. (1980). Ecology of otters in northern Scotland, I. Otter (Lutra lutra L.) breeding and dispersion in mid-Deeside, Aberdeenshire in 1974-9. J. Anim. Ecol., 49, 713 35. JENK1NS,D. & BURROWS,G. O. (1980). Ecology of otters in northern Scotland, III. The use of faeces as indicators of otter (Lutra lutra L.) density and distribution. J. Anon. Ecol., 49, 755-74. JENKINS,D. & HARPER,R. J. (1980). Ecology of otters in northern Scotland, I1. Analyses of otter (Lutra lutra L.) and mink (Mustela vison Schreber) faeces from Deeside, NE Scotland in 1977-8. J. Anita. Ecol., 49, 737 54. JOINT OTTER GROUP (1977). Otters 1977: First Report. London, Nature Conservancy Council; Nettleham, Society for the Promotion of Nature Conservation. WAYRE, P. (1979). Otter havens in Norfolk and Suffolk, England. Biol. Conserv., 16, 73-81.