Chronic Crayfish Plague Infection and Eroded Swimmeret Syndrome in Lake Saimaa (Finland) Signal Crayfish

We present data and results from a 9-year survey (2009 – 2017) of the Lake Saimaa signal crayfish population in Finland. This population has a history of chronic infection with Aphanomyces astaci. It has now been discovered that female signal crayfish from Lake Saimaa suffer from various stages of eroded swimmeret syndrome (ESS), and male crayfish also show symptoms of ESS-like trauma (i.e., eroded swimmerets and gonopods). Our data demonstrates the prevalence of A. astaci infection, with gross symptoms prevailing throughout the duration of the entire 2009 – 2017 survey, and that prevalence of ESS among female signal crayfish is correlated with the prevalence of A. astaci infection in the population. The data shows that an increasing proportion of female crayfish suffer from ESS, and have regenerated swimmerets, however, our observations indicate that partially regenerated swimmerets do not fully function during egg hatching. Based on data and observations during the survey, we speculate that low production levels, as indicated by the low catch per unit effort (CPUE), within the Lake Saimaa signal crayfish population could be related to both high A. astaci infection levels and ESS prevalence among females. The former could be causing increasing mortality among adult crayfish and the latter could be lowering Lake Saimaa signal crayfish reproductive output.
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