otters, their habitat and conservation in northeast greece

Biological Conservation 31 (1985) 191-210

Otters, their Habitat and Conservation in Northeast Greece

S. M. M a c d o n a l d

Vincent Wildlife Trust, Baltic Exchange Buildings, 21 Bury Street, London EC3A 5AU, Great Britain

&

C. F. M a s o n

Department of Biology, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, Great Britain

A B S T R A C T

In 1983, in northeastern Greece, lO00m of waterway at 52 sites were searched for signs o f otters Lutra lutra L. while the habitat was assessed for its suitability to otters. The otter was scarce in the west o f the study area (Axios and Aliakmon catchments) and was most widespread in the east ( Nestos catchment and neighbouring rivers). Nevertheless, a decline had occurred in this eastern area since 1981, though it was confined to the lowlands.

The riparian vegetation is described. Overall the Nestos catchment had the best cover, while upland rivers had greater cover than lowland rivers or canals. Sprainting intensity by otters was correlated with the amount o f cover. Rubus was especially important to otters on upland rivers, Salix on upland and lowland rivers and Phragmites on canals.

The apparent decline in this internationally important otter population is o f some concern and recommendations for its conservation are presented.

I N T R O D U C T I O N

In 1981 a field survey for otters in Greece revealed the presence of widespread and healthy populat ions (Macdonald & Mason, 1982a). Two

191 Biol. Conserv. 0006-3207/85/$03.30 © Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain

192 S. M. Macdonald, C. F. Mason

hundred sites were visited and otters were found at 62 ~ . The Greek otter populations are of international importance in view of recent severe declines throughout much of Europe. Within the south of its range the animal is endangered in Italy (Macdonald & Mason, 1983a) and sharp declines have occurred in France, Spain and Yugoslavia (Green & Green, 1981; Elliot, 1983; G. Liles and L. Jenkins, pers. comm.). In Tunisia and Morocco localised populations survive but distribution is limited by lack of water and by a lack of vegetation on rivers flowing through semi- deserts (Macdonald & Mason, 1983b, 1984). Only in Portugal is the species known to be both widespread and common (Macdonald & Mason, 1982b).

Many countries are now aware of the plight of the otter but most conservation effort is concentrated in northern Europe where populations are often severely depleted and fragmented. The conservation of healthy otter populations could be more productive and should be undertaken promptly. The otters in Greece may be now threatened by agricultural advancement and by changes in land use concurrent with the establishment of Greece in the E.E.C. Persistent pesticides used in agriculture, for example, have been cited as a major cause of decline in British otters (Chanin & Jefferies, 1978). The quality of cover provided by bankside vegetation also affects otter distribution (e.g. Macdonald & Mason, 1983c) but destruction of riparian habitat is widespread throughout Europe.

The aim of the present study was to investigate in detail those features of Greek rivers which may influence the survival of otters. Comparisons were made between areas where the animals were found to be common in 1981 and adjacent areas where declines were thought to have occurred. Work was concentrated in northern Greece with the ultimate objective of providing a conservation strategy for the otter in that region.

METHODS

The study area was surveyed from 28 July to 10 August 1983, inclusive. Fifty-two sites were visited, including upland and lowland stretches of rivers and irrigation canals and ditches.

At each site, 1000 m of waterway on both banks were searched for signs of otters. Studies have shown that a search of 600 m on one bank is

Otters in Greece 193

sufficient to establish the presence of otters in a particular stretch (Macdonald, 1983). All spraints (faeces) were counted and measurements were made of any footprints left in mud or sand. Wherever possible, searches were made from the water.

In each 50 m stretch, those features of habitat considered of potential importance as cover for otters were recorded. The overall habitat and individual plant species or mixtures of species were assessed in each 50 m stretch on the following scale.

0---cover absent l --present , but offering no suitable cover for otters 2--present in patches, offering some cover for otters 3--large area of suitable cover for otters 4- -cont inuous dense vegetation, providing excellent cover for otters

At each site, the scores for each 50 m stretch were summed to provide an index of cover for overall vegetation and for individual components out of 80. This was then scaled to 100 to provide an estimate of percentage cover.

At each site notes were made of potential prey species, visible pollution, adjacent agriculture and any use being made of the waterway.

RESULTS

Distribution and status of the otter in northern Greece

Of the 52 sites surveyed for otters in 1983, 43 (83 ~o) proved positive. This is similar to the survey results in the same general area in spring 1981, when 44 (79 ~) of 56 sites proved positive for otters.

The number of spraints found at positive sites in 1983 ranged from 1 km-1 to 102 km-1 . The intensity of marking was divided into five categories viz 0 (absent), 1 (1-10 spraints k m - 1), 2 (11-20 spraints k m - 1), 3 (21-30 spraints km - 1), 4 ( > 30 spraints km - 1). Although the distances searched for signs of otters in the 1981 survey were never more than 600 m and at positive sites were frequently less, the data (from Macdonald & Mason, 1982a and unpublished) can be scaled for comparison with the 1983 survey. The comparison is made in Figs 1 and 2. In both years otter activity, as measured by sprainting intensity, was greatest in the eastern

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196 S.M. Macdonald, C. F. Mason

TABLE 1 A Comparison of Marking Intensity by Otters in River Catchments in Northern Greece in

1981 and 1983

Otters absent Low-moderate marking High marking % sites (1-30 spraintskm -1) (>30 spraintskm -1)

% sites % sites

No. of sites

Overall 1981 21 43 36 56 1983 17 58 25 52

Aliakmon/ 1981 40 60 0 5 Axios 1983 83 17 0 6

Strymon 1981 30 50 20 20 1983 9 82 9 11

Nestos 1981 4 32 64 25 1983 6 60 34 32

Note that the overall total includes data from some small catchments not considered in the breakdown of results.

part o f the study area, i.e. in the catchment of the River Nestos and smaller rivers to the east (hereafter referred to as Nestos). Few signs of otters were found in 1981 or 1983 in the catchments of the Aliakmon or Axios, while the catchment of the Strymon River had an intermediate level of marking.

F rom an examination of Figs I and 2 it appears that a decline may have occurred between 1981 and 1983 and this is examined further in Table 1. The absence of otters at many sites in the western half of the study area and the low level of marking at positive sites here is emphasized. There appears also to have been a decline in the Nestos region and a comparison of ranks of sprainting intensity in the Nestos between 1981 and 1983 shows a significant difference (Mann-Whitney U-test, P < 0-05).

Twenty-six sites were common to both surveys. Based on the rank of the number of spraints found per km, 14 sites showed a decrease between 1981 and 1983, 7 showed no change and 5 increased. A sign test revealed a significant difference between the two years (P = 0.032, < 0.05).

The Nestos sites have been further divided into upland and lowland for comparison (Table 2). The 200 m contour was taken as the dividing contour because most of the intensive agriculture is situated below this altitude. The intensity of marking was considerably lower in the lowlands in 1983, the difference in the uplands was slight. Comparing ranks of


TABLE 2 A Comparison between Marking Intensity by Otters at Upland and Lowland Sites in the

Nestos Region, Greece, in 1981 and 1983

Otters absent Low-moderate marking % sites (1-30 spraints kin- l)

% sites

High marking ( > 30 spraints k m - 1)

% sites

No. of sites

Lowland 1981 6 31 63 16 1983 10 67 23 21

Upland 1981 0 33 67 9 1983 0 45 55 11

marking intensity using the U-test, there was a significance between 1981 and 1983 in the lowlands (P < 0.05), but the difference in the uplands was not significant.

It can be concluded that, although the otter is widespread in the study area in northern Greece, a contraction of range has occurred in the western part, which began prior to 1981. In the eastern part of the study area (the Nestos region) there is evidence of a decline since 1981, which is so far confined to the lowland area.

The riparian habitat

To provide a basic description of the riparian vegetation, the presence- absence data in the 1040 50m stretches were subject to an association analysis. Figure 3 depicts a species constellation based on positive associations (at a significance level of P < 0.001). It must be stressed that this illustrates those features of vegetation considered of value as cover for otters, it does not provide a full description of riparian vegetation. The percentage frequencies of the dominant species in upland rivers, lowland rivers and irrigation canals are shown in Fig. 4.

Riparian vegetation must be considered as a continuum, but several associations can be recognised from Figs 3 and 4. Salix spp. and Rubus agg. were generally ubiquitous. They were frequently overgrown, particularly in lowland regions, with dense tangles of climbers, especially Clematis vitalba, Calystegia sepium and Vitis vinifera. These tangles

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frequently extended into the littoral vegetation of Typha spp. and Phragmites australis, especially on canals, forming impenetrable banks of vegetation. Although the drainage canals and ditches are dredged in rotation, rapid regrowth occurs. Populus nigra and Tamarix spp. are also features of the lowland woody vegetation, the former frequently being planted, especially along canals, the latter being intermixed with Salix on the shingle beds of large rivers.

On the upland stretches of rivers, Salix spp. are joined by Ulmus minor, Alnus glutinosa and Platanus orientalis. The riparian vegetation is frequently intermixed and backed by maquis, dominated in the study area by Quercus coccifera, Juniperus spp. and Paliurus spina-christi.


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Fig. 5. The three main habitat types in the study area. (a) An upland river, with a riparian fringe of Alnus glutinosa, backed by maquis (river above Xanthi); (b) lowland river, with Alnus glutinosa, dense Salix scrub and Rubus (River Bospos); (c) irrigation

canal, choked with Phragmites australis and Typha spp. (Nestos delta).


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Photographs of the three habitat types are shown in Fig. 5. The distribution of sites in terms of percentage cover is shown in Fig. 6.

Seventeen sites (33 %) had percentage cover greater than 80 % and the majority of these were in the Nestos area. Using the overall assessment of cover for each 50 m stretch, the three major catchments and three main habitat types can be compared in terms of cover. The frequency distribution of the cover categories in the three catchments are shown in Fig. 7. An analysis by Z2 revealed significant differences in cover and the catchments can be ranked in terms of decreasing cover:

Nestos >Axios ~ Strymon ( > , P < 0 . 0 5 ; ~ , P<0 .001 )

The River Strymon catchment is assessed as having, overall, the poorest quality habitat for otters.

Figure 8 shows the frequency distribution of cover on canals, lowland and upland rivers. An analysis by X 2 showed significant differences (P < 0.001) in cover and the habitats can be ranked:

upland river > lowland river > canal

The habitat categories can similarly be broken down by catchment and analysed by X 2. There was no significant difference in cover on canals in

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the three catchments , but there were significant differences (P < 0.001) between upland and lowland rivers, which can be ranked:

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up land rivers Nestos > Axios > S t rymon

Sprainting intensity and vegetation cover

The relationship between sprainting intensity (nos. spraints per km) and percentage cover was examined using Spearman rank correlation. Using data for all 52 sites, a significant correlat ion was found (r s = 0-49, df = 50, P < 0.001). I f the Nestos data are analysed separately, the correlation is improved (r s = 0.73, d f = 30, P < 0.001), whereas there is no significant relationship between percentage cover and sprainting intensity on the S t rymon or Axios, either considered separately or combined (P > 0-05). A l though the habitat on the S t rymon and Axios is poorer than on the Nestos (see above), much of it is nevertheless perfectly suitable for otters. The absence of a relationship between marking intensity by otters and cover on these catchments suggests that some other factor has been responsible for the decline of otters.

The Nestos data can further be broken down into upland and lowland sites. The relationship between mark ing intensity and percentage cover is significant (lowland, r s = 0.63, df = 19, P < 0-01 ; upland, r~ = 0.78, df = 9, P < 0.01). Similarly, the data can be divided into irrigation canals and rivers and the relationship holds (canals, r s= 0.76, d f = 10, P < 0.01; rivers, r~=0.77, d f = 18, P < 0 . 0 1 ) . The relationship between marking intensity and percentage cover of vegetation thus holds over all habitats in the Nestos area.

The relationship between marking intensity by otters and individual componen t s of vegetation was also examined for the Nestos data. Overall, marking intensity was related to Rubus cover (r~ = 0.48, df = 30, P < 0.01), but a b reakdown of sites into upland and lowland reveals a significant relationship only with Rubus in upland sites (upland, r s = 0.70, d f = 9, P = 0-05; lowland, r~ = 0-33, df = 19, NS). There is a significant relationship between marking intensity and Salix cover in both upland and lowland sites (upland, r~ --- 0.39, df = 9, P < 0-05; lowland, rs = 0-41, d f = 19, P < 0-05). There is a significant correlation between marking intensity and Phragmites cover on canals (r~=0-83, d f = 10, P < 0-01). For other species of vegetation there were insufficient data t o


allow comparison. It should be noted that the riparian vegetation is a constantly changing mixture of individual species in close juxtaposition so that the overall relationship between sprainting intensity and cover is likely to be stronger than that between individual components.

Additional observations

Throughout the study area, exposed mud or sand made it possible to measure otter tracks. Measurements were taken across the forefoot from the extremities of toes 1 to 5. Clearly track sizes vary with substrate but a print of over 70 mm was considered as representing a male otter and tracks of 45 mm or less, a cub. Small (cub) tracks were found in association with larger (presumed female) prints. It is not possible to differentiate between females and juvenile males but it is often possible to establish whether more than one animal is present in a particular area. Tracks were found at 17 of the sites visited. At 5 of these sites cub(s) were present and at a further 4 sites a male together with at least one other animal was present. At the other 8 sites the tracks suggested the presence of solitary animals with prints of intermediate size.

All five records of cubs were from the east of the study area, four being in good habitat and one in habitat of moderate value. Of the other sites with more than one otter present, three were in good habitat and one in moderate habitat. At sites thought to contain lone animals, the habitat was good at three, moderate at one and poor at four. Combining all sites with more than one animal, there were averages of 14.2 sprainting sites and 43-3 spraints per km. With apparently lone animals there were averages of 10.3 sprainting sites and 16.5 spraints per km.

Note was made of the locations of 255 sprainting sites (800 spraints). Forty-three per cent of sites were rocks and stones in or close to water. A further 36 ~ were on mud, sand or gravel. The majority of the remainder were ledges under bridges or grass. Logs or trees were found as sprainting sites only four times.

The distribution of numbers of spraints per sprainting site shows a consistency between rivers whether upland or lowland. On canals more sites had 10 or more spraints present; this is due to the relative scarcity of sites on overgrown canals. Available sites tend to be heavily marked.

It was considered that otters usually were finding resting sites above ground in dense riparian vegetation. Only two specific resting sites were identified. One site consisted of large boulders overgrown with Rubus


fronted by mature A lnus and backed by maquis. The tracks of a small cub and a presumed female otter entered this site. The second resting site consisted of a steep sand bank densely vegetated with Salix scrub, Rubus and Tamarix spp. Wet prints on dry sand indicated that a male otter had entered this site at dawn. Both resting sites were within 5 m of the water.

Note was made of the agriculture at all sites visited. Maize was grown throughout the area and was the major crop of the eastern lowlands. On eastern foot-hills tobacco was cultivated, but much of the uplands can only be used for rough grazing. In the west of the study area more cereals like barley and wheat were grown and tomatoes and cotton were important crops.

Records were kept of visible water pollution. Most rivers were eutrophic but clean; slight organic pollution was noted at only six sites.

Prey availability was not considered to be limiting to otters. Fish, amphibians, crabs and snakes were apparently abundant.

Human disturbance on rivers was generally caused only by agricultural workers. Extraction pumps for irrigation were frequent in the lowlands. Some rivers appeared to be heavily fished often by use of gill and fyke nets. One fisherman on the River Strymon claimed to have caught two otters in fyke nets.

DISCUSSION

Because otters are secretive, thinly distributed and largely nocturnal, their presence and status have to be assessed by counting the number of signs, particularly spraints, left by the animals on waterways. There are a number of factors influencing marking intensity (Macdonald & Mason, 1983c), so that this measure cannot be used as a direct indication of population size. Nevertheless, there is a general relationship between the level of marking and the success of the population, with fragmented, declining populations leaving fewer signs than healthy breeding ones.

Our results show that, although the otter remains widely distributed in the study area, a sharp decline has occurred in the west. These fragmented populations were also noted west and north of Thessaloniki in 1981 (Macdonald & Mason, 1982a) so this decline occurred prior to that date. The 1983 results also suggest a decline since 1981 in the eastern part of the study area, a region previously considered to hold one of the healthiest populations in southern Europe. Otters are known to vary their marking


intensity with season (Erlinge, 1967; personal observations). It could be argued, therefore, that the present survey coincided with a seasonal decrease in marking activity. However, significant declines occurred only in the lowlands of the eastern area. The level of marking in upland areas in 1983 remained high. It was, for example, higher than in our study sites in Wales (personal observations) where good otter populations occur and it was equivalent to summer marking intensity in Portugal where the animal is widespread and common (Macdonald & Mason, 1982b). It is concluded, therefore, that the decrease in the lowland Nestos area between 1981 and 1983 is genuine. Regular monitoring of the area is required.

The level of marking in the Nestos was highly correlated with vegetation cover in upland rivers, lowland rivers and irrigation canals. The riparian vegetation is a complex, interwoven mixture of species, highly variable from site to site, due to natural and anthropogenic factors. There were significant correlations between marking intensity and cover provided by the dominant species Salix, Rubus (in uplands) and Phragmites (in canals), but the dense tangles of species interweaving these dominants are likely to be of importance in the structure of otter habitat. A similar study in Wales (Macdonald & Mason, 1983c) revealed the importance of mature ash Fraxinus excelsior and sycamore Acer pseudoplatanus root systems as secure resting sites for otters. In Greece such tree root systems are rare. Otters undoubtedly use the luxuriant, impenetrable growths of scrub and climbers as lying-up sites. Above- ground breeding sites would be adequate where cover is dense and disturbance low.

There was no correlation between vegetation cover and marking intensity in the western part of the study area. Although the habitat was of poorer quality than in the east, it was considered to be adequate for otters. The decline of the species in this area is likely to be due to other causes. Similar conclusions were reached in France and Yugoslavia (Green & Green, 1981; G. Liles and L. Jenkins, pers. comm.)where otters could not be found in areas still offering suitable habitat. In these countries and in Spain (Elliot, 1983) otters are more commonly found in the uplands, while lowland waters are frequently polluted.

In Britain, declines in otters were attributed to pollution by persistent pesticides, especially dieldrin, but this conclusion was only reached circumstantially 20 years after the major losses had occurred (Chanin & Jefferies, 1978). The present situation in northern Greece may be


equivalent to the position in Britain in the early 1960s and so presents an opportunity to identify any chemical compounds which may be adversely affecting otters. The organochlorines dieldrin and DDT, for example, are still widely used in Greek agriculture (C. Kondoyiannis, pers. comm.). In the plains of the River Strymon and to the west of Thessaloniki there is intensive cereal production. Dieldrin is frequently used in cereal seed dressings. The Axios lowlands have, since the 1950s, been major rice- producing regions where DDT was extensively used for mosquito control. In other rice-growing areas of Europe, like the Camargue in France or the Ebro delta in Spain, otters are now absent (L. Hoffmann, pers. comm.; Elliot, 1983). By contrast, in northeast Greece maize is the most extensively grown crop and is less susceptible to pests than other cereals (Milbourn, 1975). However, the current decline in otters here suggests the recent introduction or increased use of some deleterious pollutant.

Although the relative quantities of chemicals used in Greek agriculture have been low by comparison with the rest of the EEC (Tsoukalis, 1979), this position is likely to change.

In southern Sweden the loss of otters has been attributed to PCB contamination (Sandegren et al., 1980). Kilikidis et al. (1981) recorded PCBs in marine organisms from the Strymonikos Gulf of the Aegean Sea and cited the River Strymon as one source of this pollution. The major rivers within northern Greece may well accumulate pollutants before their waters enter Greece. The Axios and Strymon catchments include large towns and areas of intensive agriculture in Yugoslavia and Bulgaria respectively. By contrast, the Nestos has a predominantly mountainous catchment, more distant from urban and agricultural development.

While the destruction of riparian habitat may not pose immediate problems for otters in northern Greece, this situation could also change under economic pressures. On lowland irrigation ditches otters appeared to be dependent on cover provided by dense growths of Phragmites. The current regime of ditch clearance (on a 4 or more year cycle) provides sufficient waterways choked by vegetation. Reed sales at present provide additional income for farmers but any increased use of herbicides as opposed to manual cutting, could deprive the otters of shelter. In many European countries, e.g. Britain and italy, bankside scrub is regularly removed for flood prevention or to provide additional farmland. The current average size of Greek farms is only 6 ha but smallholdings are now being amalgamated into larger units (Pantelouris, 1980).

Throughout Europe otters are frequently drowned in fish traps (e.g.


Stubbe, 1977; Heidemann, 1980). During the present study many fyke nets were encountered and one fisherman claimed to have caught two otters. In Britain efforts are being made to prevent such mortalities by the introduction of a mesh across the entrances to fyke nets. Enforcement of similar measures in Greece could prove difficult.

Greece holds one of the best populations of otters in southern Europe. Nevertheless, declines are occurring, probably due to increased use of persistent chlorinated hydrocarbons. It is essential that information be gathered on the types and quantities of pesticides currently used in agriculture. Fish tissues should be analysed for pesticide residues, as should the bodies of any otters which become available, for example from road kills or drownings in fish-nets.

Other practical conservation measures could be taken to safeguard these important otter populations. The feasibility of setting up protected zones in riparian habitat (river parks) should be investigated. These would protect otters, their habitat, and incidentally many other species. The riparian zone in Greece is owned by the State, which should theoretically make the establishment of reserves easier than in countries such as Britain, where river banks are in private ownership.

The otter could form the focus of an educational programme in conservation for the public and in schools. Considerable public empathy has been generated over the plight of the otter in western Europe and the species could be a valuable symbol for conservation in Greece.

It is clear that, if the otter population in Greece is not to follow the fate of most of those in western Europe, a positive strategy for conservation is needed now.

A C K N O W L E D G E M E N T S

This project was financially supported by the Otter Specialist Group of the IUCN. We would like to thank Dr Nicole Duplaix and Dr F. Wayne King for their interest.

REFERENCES

Chanin, P. R. F. and Jefferies, D. J. (1978). The decline of the otter Lutra lutra L. in Britain: An analysis of hunting records and discussion of causes. Biol. J. Linn. Soc., 10, 305-28.


Elliot, K. M. (1983). The otter (Lutra lutra L.) in Spain. Mammal Rev., 13, 25-34.

Erlinge, S. (1967). Home range of the otter Lutra lutra L. in southern Sweden. Oikos, 18, 186-209.

Green, J. & Green, R. (1981). The otter (Lutra lutra L.) in western France. Mammal. Rev., 11, 181-7.

Heidemann, G. (1980). Zur Lage des Fischotterbestandes in Schleswig-Holstein (Bundesrepublik Deutschland): In Der Fischotter in Europa-Verbreitung, Bedrohung, Erhaltung, ed. by C. Reuther and A. Festetics, 145-51. Oderhaus and Gottingen, published privately.

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