Gathering local knowledge to detect distribution and threats of Tachypleus tridentatus in Beibu Gulf, China

While there are increasing reports in Asia regarding the population declines of Chinese horseshoe crab, Tachypleus tridentatus, their population and ecological status in China are very limited. We conducted community interviews in 29 fishing villages and small towns around Beibu Gulf in Guangxi, China to collect information on the potential spawning/nursery shores of T. tridentatus and imminent threats to the population. Based on the results from 407 respondents, we have identified 43 potential shores which are evenly distributed along Beibu Gulf shores. The presence of juvenile T. tridentatus on ten shores were verified by the population survey. Nearly all the respondents (95 %) observed an overall reduction in T. tridentatus population, which believed to be mainly attributed to the unsustainable fishing practices. Respondents with sighting experience of the horseshoe crab spawning on shores were significantly older, suggesting the considerable reduction in the total number of T. tridentatus mating pairs with time. Meanwhile, the average daily harvest of the adult horseshoe crabs declined sharply from the approximate range of 50–1,000 in the 1990s to 0–30 individuals at present. As the formulation of conservation measures is urgently required, such “Wisdom of Crowds” method, supplemented with confirmatory field surveys, may be of important values by providing general information on the population status and threats of T. tridentatus in Asia-Pacific regions where well-structured population monitoring is unaffordable.