Observational study reveals river water levels correlate with body condition in migrating Pontic shad, indicating female energetic status is vulnerable to hydrological changes.
The Pontic shad (Alosa immaculata), an ecologically and commercially important anadromous species of the Danube–Black Sea basin, undergoes spawning migration under variable hydroclimatic conditions. This study assessed the evolution of body condition during spawning migration in the lower Danube (river km 133–197) between 2020 and 2025. A total of 2,130 individuals were analyzed, and Fulton’s condition factor (K) was calculated from length and weight measurements. Significant interannual differences in K were detected in both males (χ² = 92.503, p < 0.001) and females (χ² = 142.47, p < 0.001). In males, variation was primarily driven by 2023, whereas females exhibited a stronger and delayed divergence, with 2025 differing significantly from all other years. Spearman correlations indicated a positive association between K and river water level in both sexes, moderate in males (ρ = 0.6) and strong in females (ρ = 0.829), suggesting that hydrological variability influences energetic status during migration. These findings highlight significant interannual restructuring of somatic condition in A. immaculata, with females showing greater sensitivity to hydroclimatic variability, potentially affecting reproductive performance and population resilience.
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LEONOV et al. (2026) studied this question.
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