Genetic Insight Into the Diversity and Population Structure of the Noble Crayfish ( <i> <scp>Astacus astacus</scp> ) </i> in the Eastern Distribution Range: Implications for Conservation in Belarus

ABSTRACT The noble crayfish, Astacus astacus , is a globally threatened species experiencing population declines throughout Europe. Despite its conservation status, genetic diversity patterns remain poorly characterized across its distribution, particularly in Eastern Europe. Here, we address this knowledge gap through mitochondrial ( 16S rDNA and COI ) and microsatellite (19 loci) analyses of Belarusian populations. Our results reveal that these populations belong to previously described mitochondrial lineages 1 and 2 sensu , identifying seven mtDNA haplotypes (five novel), with the highest diversity concentrated in the Neman River catchment. This catchment not only represents a regional biodiversity hotspot but also exhibits the highest mtDNA diversity recorded for A. astacus across the entire Baltic Sea watershed, suggesting its role as a post‐glacial colonization corridor from the Black Sea basin refugium. This unique diversity now constitutes a priority for conservation. Microsatellite analyses demonstrated limited within‐population diversity but strong differentiation among populations, indicating severe genetic erosion in isolated groups. Our analyses support a hierarchical conservation framework with two Evolutionarily Significant Units (ESUs) corresponding to the Baltic and Black Sea basins, and multiple Management Units (MUs) within river catchments, which has direct implications for conservation management. Populations from lotic environments exhibited significantly higher genetic diversity than lentic ones, highlighting the vulnerability of these lentic populations. We strongly recommend catchment‐specific conservation strategies, particularly regarding translocations, to preserve A. astacus 's unique local adaptations and genetic integrity, and to prevent genetic homogenisation. We also propose considering within‐catchment genetic rescue efforts for small, inbred populations. These strategies are critical to preserving A. astacus 's adaptive potential and preventing regional extinctions.