Abstract

The physiological condition of a crayfish stock affected by peat mining runoff waters was studied in two locations; one downstream and the other one upstream of the peat mining area. The results were compared with results from a nearby river without the peat mining effects and a pond with dense crayfish stock. We measured population densities, and the moisture and energy contents of the hepatopancreas on individual crayfish at different sites. We found that in the area upstream of the peat mining area density was 0.5 ind. m^-2, while the average moisture percentage of the hepatopancreas was 74.0% in males and 70.4% in females. The energy content of hepatopancreas was 28.77 kJ g^-1 in males and 30.10 kJ g^-1 in females. In the area downstream of the peat mining area density was 1.0 ind. m^-2, the average moisture percentage of the hepatopancreas was 81.8% in males and 75.2% in females, the energy content was 24.20 kJ g^-1 in males and 26.40 kJ g^-1 in females. However, we conclude that it is difficult to separate the possible effects of peat mining on crayfish stocks in a river as most of the nearby 'natural' (control) waters are also high in humic contents, and all the rivers have altered habitats after past dredgings. The trapping pressure is only light and occasional, and thus we do not know to what extent these crayfish stocks can stand trapping in these rivers, which could be a good long-term measure of the condition of the stocks.

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