Multi-year quantitative eDNA monitoring reveals temperature-driven spawning migration phenology of Pacific herring (Clupea pallasii) in a temperate coastal embayment

초록

Monitoring the spawning migration of Pacific herring (Clupea pallasii) is essential for stock assessment and habitat protection. However, conventional survey methods often lack the temporal and spatial resolution required to accurately define spawning timing. This study employed quantitative environmental DNA (eDNA) to characterise the spawning migration phenology of C. pallasii in Jinhaeman Bay, Korea, over three years (2019-2022). Species-specific quantitative polymerase chain reaction assays were integrated with coastal fisheries catch statistics and water temperature profiles. The results indicated sharp increases in eDNA concentrations during winter, with peak activity occurring between December and February depending on the year. Significant bottom concentrations of eDNA at key spawning hotspots demonstrated extreme spatial concentration and strong site fidelity to shallow vegetated habitats. While commercial fisheries recorded initial catches in November, eDNA was not consistently detected inside the bay until December-January, indicating a temporal lag between coastal arrival and inner-bay spawning ground occupancy. Bottom eDNA concentrations exhibited a significant inverse correlation with water temperature (Spearman's rho = -0.70, p < 0.001), with initial spawning ground occupancy consistently observed as temperatures approached approximately 10 C-degrees. This thermal association-together with a temperature-linked arrival but temperature-independent departure evident across spawning cycles-indicates that spawning phenology in this population is governed by bounded phenological plasticity, constrained by physiological thermal requirements rather than freely adjustable to interannual variability, and consistent with hatching-success optima previously reported for Pacific herring. By resolving this asymmetric phenological structure at a temporal and spatial resolution unattainable through conventional survey methods, quantitative eDNA monitoring establishes a framework for anticipating climate-driven shifts in spawning timing and spawning-ground occupancy, with direct application to early warning systems for coastal fishery management under changing oceanographic conditions.

키워드