# Winter occurrence and spawning characteristics of Pacific herring (Clupea pallasii) in Jinhae Bay: An integrated survey using acoustic monitoring, gillnet sampling, and environmental DNA

## TL;DR

This study tracks Pacific herring in Jinhae Bay during winter using sound, nets, and DNA to understand their spawning patterns and support conservation.

## Contribution

The study integrates acoustic monitoring, gillnet sampling, and eDNA to comprehensively assess herring spawning dynamics in a key winter spawning ground.

## Key findings

- Herring school signals were detected from mid-January to mid-February, aligning with peak gillnet catches.
- eDNA concentrations peaked in mid-January and declined afterward, indicating spawning activity.
- Most herring females were ripe or spent, confirming peak spawning during the study period.

## Abstract

This study investigated the adult density, timing of migration, and biological characteristics of Pacific herring (Clupea pallasii) entering Jinhae Bay, South Korea, in winter, a major spawning ground for the species. A wideband autonomous transceiver (WBAT) was deployed from November 2022 to March 2023, and standardized gillnet surveys and environmental DNA (eDNA) were conducted concurrently. WBAT monitoring showed that C. pallasii school signals appeared predominantly from mid-January to mid-February, coinciding with the period during which herring were highly dominant in gillnet catches. Assessment of female reproductive maturity indicated that most individuals were ripe or spent, confirming that this period represented the peak spawning season. eDNA concentrations exhibited a sharp peak in mid-January in both surface and bottom waters and then declined steadily thereafter. Taken together, these results indicate that entry into the spawning ground begins in late-December, peaks in mid-to-late January, and declines toward late-February. By integrating acoustic, catch, and eDNA datasets, this study provides a comprehensive assessment of the timing, density, and spawning ecology of C. pallasii, offering evidence-based guidance for future resource management and spawning-ground protection in Jinhae Bay.