1. The striking variation in fecundity of the noble crayfish (Astacus astacus) was assessed from 1981 to 2009 in the lake Steinsfjorden, Norway.
2. Egg size showed no distinct variation with crayfish size or between years and seems to be a fairly fixed property. Ovarian egg numbers increased linearly with body size, from a mean of 70 eggs at maturity to nearly 250 eggs in the largest individuals. There were strong and significant interannual differences in the size-specific fecundity, and variation in size and among years explained 60% of the observed variance in fecundity.
3. The proportion of mature females in the population ranged from 0.068 to 0.817, with extreme year-to-year fluctuations. The proportion of mature females increased significantly over the years, in parallel with increased temperature, but we were unable to link maturity with ambient temperature either in the same year or in the previous year.
4. While several indices point to increased crayfish productivity with higher temperature in this population, there is also a complex and apparently chaotic interplay between life-cycle attributes, density-dependent parameters and ambient conditions that lead to high variability in annual recruitment. This probably reflects the slow and delayed life-cycle responses to a changing environment.