Threats assessment of the endemic idle crayfish (Austropotamobius bihariensis Pârvulescu, 2019)

The idle crayfish (Austropotamobius bihariensis Pârvulescu, 2019), endemic to Romania's Apuseni Mountains, urgently requires a specific conservation plan. Due to its recent description, conservation efforts have been limited, highlighting the need for immediate and practical recommendations to ensure its protection. Over 13 years, field observations were conducted to evaluate population trends and identify threats following IUCN standards. Additionally, geospatial assessments and predictive modelling were employed to estimate both the optimal habitat and current population size under three distinct scenarios. The primary threats identified include poor forest management, extreme drought, anthropogenic development and riverbed alterations, all contributing to declines in crayfish abundance. The most severe impacts arise when these pressures converge at a single site, compounded by a chronic, low-virulence crayfish plague infection (A-haplogroup). The total population is estimated at 31,150 (± 449.9 SE) individuals, with 1,163,754 m$^2$ of suitable habitat, of which only 37.9% lies within 13 protected areas under the most realistic scenario. Poor water quality was found to significantly reduce the modelled population size. In light of these findings, we propose a series of targeted conservation actions tailored for each protected area and highlight the importance of extending measures beyond their current boundaries. Additionally, we recommend implementing the ‘ark sites’ concept in regions with optimal ecological conditions, stable populations and genetic diversity, to reduce pressures and safeguard the species through effective field management.