Estimating the human impact on populations of the endangered noble crayfish (Astacus astacus L.) in north‐western Poland

• 1. The Pomorskie Lakeland close to the town of Miastko shows the highest density of stocks of the noble crayfish Astacus astacus (L.) in the lowlands of north‐western Poland. In summer 2002, the present status of this highly threatened species was analysed by means of mark and recapture trapping.
• 2. Nine lakes with known occurrence of A. astacus were investigated. Each lake was surveyed with regard to the crayfish population density, water quality and potential recent and historical impact of fisheries and recreation. The estimated population density was evaluated statistically with respect to a set of potential environmental variables.
• 3. The estimated densities of A. astacus populations varied from very abundant (6.6 adult individuals per trap per night) to absent. Two lakes were found to contain the non‐indigenous crayfish Orconectes limosus (Raf.). The population density was not correlated with conductivity, pH, transparency, alkalinity, the concentration of ammonium, calcium, chloride, nitrate, nitrite, total nitrogen, total phosphorus, or with the trophic status of the lakes. A. astacus occurred in lakes ranging from mesotrophic to eutrophic.
• 4. The results suggest that both occurrence and density of A. astacus populations depended on criteria associated with human activities that have altered the aquatic environment. Abundance of A. astacus was negatively correlated with eel (Anguilla anguilla) stocking intensity (r = ?0.88; p < 0.01) and number of yearly net catches (r = ?0.66; p < 0.05) and positively correlated with distance to nearest town (r = 0.72; p < 0.05).
• 5. It is concluded that the introduction of O. limosus most likely resulted from fishery activities, emphasizing the need for regulations to reduce the negative impact of lake fisheries on native crayfish stocks.

Copyright © 2005 John Wiley & Sons, Ltd.