Status, habitat use, and gear-specific conservation of threatened seahorses: The first integrated assessment in Taiwan

Abstract

Seahorses (Syngnathidae: Hippocampus) are among the most threatened marine fishes globally due to habitat degradation and overexploitation. This study provides the first comprehensive assessment of seahorse populations in Taiwan, integrating scientist-led underwater and landing surveys, fisher interviews, and citizen science, conducted between 2021 and 2022. We identified five species (H. kuda, H. histrix, H. kelloggi, H. spinosissimus, and H. trimaculatus), excluding pygmy seahorses, through morphological and molecular analysis in this study. Underwater visual census (UVC) revealed a pooled density of 0.0002 individuals/m(2), which is substantially lower than global densities for seahorse wild populations. Genetic analysis revealed contrasting evolutionary histories, while the pelagic-rafting H. trimaculatus exhibited high connectivity and diversity. H. spinosissimus showed extreme genetic isolation (FST approximate to 0.98) and H. kuda displayed evidence of recovery from historical depletion. In situ surveys indicated a high reliance on artificial marine debris and sea urchins as holdfasts. Finally, fisher interviews indicated an extremely-low post-capture survival rate (<10%) for trawl bycatch, rendering release ineffective for this sector. We therefore propose a gear-specific conservation strategy: implementing spatial exclusion zones to restrict trawling in identified hotspots, while mandating quick-release" protocols specifically for the survivable crab-trap fishery."