Niche‐based species distribution models and conservation planning for endangered freshwater crayfish in south‐western Germany

1. Niche‐based species distribution models (SDMs) can help conservation planning by forecasting environmental suitability for an endangered species. Here, SDMs were constructed for stone crayfish (Austropotamobius torrentium) and white‐clawed crayfish (Austropotamobius pallipes s. str.) to identify catchments in south‐western Germany where environmental conditions are favourable for reintroduction.
2. Maximum‐entropy modelling (Maxent) was used with presence‐only data to forecast environmental suitability for the two crayfish species based on five climate variables, slope, land cover, and a human impact index.
3. SDMs showed good to excellent performance and were able to capture the range of both Austropotamobius species. Presence probabilities were mostly determined by climate variables, and climate niches partly overlap, with white‐clawed crayfish occurring at conditions with less extreme winter temperatures and lower temperature seasonality than stone crayfish. Human impact contributed between 10 and 27% to the models and was negatively related to presence probabilities. Contribution of land cover was low (5%) but showed a positive relationship with deciduous broadleaf forest in both species.
4. Both SDMs indicated several catchments with high predicted environmental suitability but no present occurrence records. Subsequent crayfish and habitat surveys in these catchments revealed four streams considered suitable for reintroduction and led to discovery of five previously unknown white‐clawed crayfish populations. Overall, SDMs proved to be a powerful tool for conservation planning of freshwater crayfish species.