The impact of raised water level on a winter anoxia lake on the population of narrow-clawed crayfish Astacus leptodactylus (Esch.)

The impact raised water level in the winter anoxia Oswin Lake (Poland) had on the population of narrow-clawed crayfish, Astacus leptodactylus (Esch.) was determined. Raising the water level in the lake increased the surface are from 360 ha to 900 ha and improved habitat conditions. The species diversity of vegetation increased, as did the area of lake bottom covered by it (from 22 to 51 percent). The threat of winter anoxia was also reduced. The share of individuals measuring more than 10 cm increased from 76 percent in 1991 to 95 percent sixteen years after raising the water level. During this period (1991-2007) the mean total length of crayfish increased significantly statistically (P lesser 0.05) from 10.5 to 12.7 cm. This means that during this period, the life expectancy of the dominant crayfish age group increased by about two to three years