The national survey of the early 1990’s proved that otters were prevalent throughout Poland, with their presence identified at 79.5% of investigated sites (Brzeziński et al., 1996). However despite this relatively high density, only a few positive sights were recorded in two large areas: Silesia and Central Poland. Within the latter region, otters were absent in almost the entire catchment of the River Bzura. The only positive sites recorded within this area were at the confluence of the Rivers Bzura and Vistula, and along the River Rawka. The absence of otters in the rest of the catchment has been associated with exceptionally high municipal and industrial sewage disposal to Bzura, which by the late 1980s was totally inadequate.

In the autumn of 1995, the first otter presence was recorded on the lower River Bzura. This discovery prompted a comprehensive survey of the catchment in order to document recent changes in otter distribution within this area. Also included in the survey was Warsaw and its environs, an area that had previously recorded only few positive sites. The study area was relatively well populated, with many towns, villages and agricultural land. The method used was the standard field survey based on a UTM 10 km square grid (see Macdonald, 1983). In each square 2 - 4 sites were investigated. In addition, spot checks were conducted at the majority of road bridges within the region to complement the surveys.

Initial results of the spring 1996 surveys have been promising. Out of 46 full surveys undertaken, 54% were positive as were 37% of 95 additional spot checks, indicating that otters are present in the majority of tributaries within the lower catchment and further upstream on the River Bzura itself. Whereas the otter was absent during the national survey, today, the Rivers Utrata, Pisia and Lasica have all recorded positive sites. It was very satisfying to find that otters are now present in the rivers and channels of the Kampinos National Park (part of the lower Bzura catchment) where the species was previously extirpated in the early seventies (Bieniek, 1992). The recolonisation of  the park by otters since the national survey of 1993 (when it recorded no positive evidence of otters) coincided with the increase of the beaver population. Today the beavers appear to be thriving, and we have repeatedly found otter signs on one canal where there is much evidence of  beaver activity.

The surveying of Warsaw city and its surrounding district has also shown positive results. Here, otters have been found to be present on small channels and fishponds in the south side of the city within heavily developed areas. Signs of otters have also been found over several waterways in the eastern suburban districts. This area is well linked not only to the River Vistula, but also to the Rivers Bug and Narew by several canals and it is apparent that otters have taken this opportunity to colonise suboptimal habitats, where high levels of human interference do not apparently bother them.

Although some authors suggested increase in otter numbers in Poland in late 1980’s (Wlodek et al., 1989), the results reported for Central Poland represent first well documented evidence of recovery of the species. The marked increase of otter presence can probably be attributed to a recent reduction of effluent entering the waters due to better treatment techniques. The recovery of the otter population in Central Poland is an ongoing  process, and  otter presence in the Bzura catchment is a good illustration of this. Closer to the main source of pollution (upper Bzura), very few positive sites were recorded in the survey and several tributaries completely lacked otters. This shows that recolonisation of the catchment is incomplete. We believe that after the new sewage treatment stations for industries in Lódz area (currently under construction) are brought into service, the subsequent improvement of water quality will enable otters to eventually recolonise the upper Bzura and all of its tributaries.

REFERENCES

Bieniek, M. (1988). The otter, Lutra lutra (L.) in Poland's national parks. Ochr. Przyr. 46: 195-215. [In Polish with English summary]
Brzeziñski, M., Romanowski, J., Cygan, J. P., Pabin, B. (1996). Otter Lutra lutra distribution in Poland. Acta Theriol. 41: 113-126.
Macdonald, S. M. (1983). The status of the otter in the British Isles. Mammal Rev. 13: 11-23
Wlodek, K., Lapiñski, W., Gielo, M., Sobolewski, H., Rösler, A. (1989). Expansion des Fischotters Lutra lutra (L., 1758) in Polen. Populationsökologie Marderartiger Säugetiere, Wiss. Beitr. Univ. Halle 1: 44-54.

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