Alarming biological indicators and management implications for the Critically Endangered Taiwanese wedgefish (Rhynchobatus immaculatus) in the Taiwan Strait

According to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, all but one wedgefish species are classified as Critically Endangered, underscoring the urgent need for action to prevent extinction. The Taiwanese wedgefish (Rhynchobatus immaculatus) , first described in 2013, remains poorly understood, lacks baseline data, and continues to be exploited in Taiwan. This study addresses this knowledge gap by providing the first comprehensive assessment of its population dynamics, based on fishery-dependent monitoring conducted from January to December 2024. Length-frequency data revealed monthly variations, with the catch dominated by immature individuals below the optimal length. Growth parameters indicated that the species is slow-growing (L inf = 219.1 cm, total length; k = 0.075 year⁻¹) with a positively allometric length–weight relationship (b = 3.141). The species faces high fishing pressure, with fishing mortality exceeding sustainable reference points; other metrics showed similarly concerning patterns. The spawning potential ratio is critically low at 5%, and the size at 50% capture is well below the maturity size, indicating recruitment overfishing. We recommend reducing fishing mortality by approximately 64% to prevent overfishing of juveniles and by around 78% to achieve optimal exploitation. A size-based enforced release policy (for fish under 140 cm and over 165 cm TL), a landing ban in June, and seasonal closures or effort reductions for gillnets from July to September are advised. In parallel, cooperative and precautionary management among stakeholders should be discussed in light of these findings. • 90.9% of wedgefish species are Critically Endangered, including the poorly known Taiwanese wedgefish. • First comprehensive population dynamics assessment for this species. • Findings reveal a slow-growing species under high fishing pressure, with multiple indicators confirming recruitment overfishing. • Novel life-history parameter information for this species in the region was contributed to FishBase. • Urgent management action is warranted to prevent population collapse.