INTRODUCTION

More and more animal species seem to be able to cope with human land use, e.g. beech marten, beaver, roe deer. There is also some significance that otters (Lutra lutra) are not as little flexible as we thought them to be in former years (KRANZ, pers. comm.; KRUUK, 1995). Obviously they need a certain amount of "habitat inventory" (water quality, easily reachable food, variable bank structure), but not only "natural" or completely "undisturbed" landscapes can offer these parameters. Nevertheless this should not be an excuse for lack of consideration or nonchalance and thoughtless destruction of nature.

As the plans for using the last kilometers of upstreams free running water where otters were scarce but still evident (WINKLER 1990) for building two more catchment basins became more actual, the survey was to prove whether the otters do use the already existing basins at all or disappeared completely.

METHODS

The study site was a chain of 10 catchment basins along 150 km of the river Drau in southern Austria built some 30 years ago for generating electricity. Although the basins themselves were built in the “old fashioned way” (stones and concrete, hard banks) time passed by and helped to create sites with shallow water, sediment and vegetation. Some creeks empty (even level) into the catchments and build very well structured places

The survey was done in late fall and winter 1993/94, the technique was as usual : searching for spraints and/or fottprints and other otter signs by

1. walking along the banks as detailed as my limited budget allowed,
2. controlling“special” sites as there are bridges, mouths of small rivers and creeks (and upstream)
3. controlling 80 checkpoints along the river (Mason and MacDonald, 1986)
4. visiting islands and peninsulas

Problems:

• the water level changes within short time
• waves produced by boats wash spraints and tracks away
• "wrong" season (very bad wheather! Early snowfall helped a little)

RESULTS

• 80 Checkpoints
  • 6 positive (footprints and/or spraints)
  • 10 uncertain (prints not complete or indistinct
  • 64 negative
• already known site (Spittal/Drau) reconfirmed
• new site (at Feistritz catchment basin) found
• Otters are very scarce at the river Drau (2 proofed sites - 150 km !)
• They use banks of catchment basins only close to the mouth of creeks (more and various bank structure, better food conditions, less polluted water)

REMARKS

Although this was a rather superficial investigation the results indicate the following :

• the density of the otter population at the river Drau seems to be very low.
• otters occur not only in undisturbed portions of the river but also along the catchment basins, but
• the catchments are probably only used to cross the river and/or to swim from one confluence of smaller creeks to the neighbouring.
• catchment basins seem to be rather suboptimal habitats for otters and only used when enough optimal “backcountry habitat” is available.

REFERENCES

Eisner, J., Sieber, J. (1993). unpublished Report: Fischotterkartierung an der Drau.
Kruuk, H. (1995). Wild Otters. Oxford University Press, New York
Mason, C. F., Macdonald, S. M. (1986). Otter: ecology and conservation. Cambridge University Press 236pp.
Winkler, H. et al. (1990). Teilgutachten 3, Ökologie ausgewählter Landtiergruppen und Wildbiologie. Bericht des ÖIR.

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