Fluctuations in harvest of native and introduced crayfish are driven by temperature and population density in previous years

The effects of temperature and density on annual fluctuations in catches of large adult crayfish are evaluated using time series analysis. We tested if temperature during different stages of the crayfish life cycle influenced observed catches from 1946 to 2007 in Lake Bunn (Sweden). From 1946 to 1974, native noble crayfish (Astacus astacus) inhabited the lake, but then, crayfish plague wiped out the whole population. In 1985, the exotic signal crayfish (Pacifastacus leniusculus) was introduced and is still present. This made it possible to model the two species separately and compare how temperature and density influence the abundance of large adult crayfish. The best models indicate that both climatic- and density-dependent factors influence the observed fluctuations and there was a time lag for most factors included in the best models. Winter temperature had the strongest influence on fluctuations of both species. Also, density dependence was included in the best model for both species. Growth season for noble crayfish and temperature during the mating season for signal crayfish were also present in the most parsimonious model. Based on our findings, it is difficult to predict how further climate warming will affect crayfish population dynamics in freshwaters.