Wisdom of Crowds reveals decline of Asian horseshoe crabs in Beibu Gulf, China

Abstract

Population decline among Asian horseshoe crabs in Asia is increasingly reported, but knowledge of their population and ecological status in China is limited. We conducted community interviews in 30 fishing villages around Beibu Gulf in Guangxi, China, to collect distribution information about the potential spawning/nursery grounds of Tachypleus tridentatus and Carcinoscorpius rotundicauda, and any imminent threats to their populations. Based on the results from 400 respondents we identified 45 potential spawning/nursery grounds distributed widely along the shores of Beibu Gulf. We visited 10 of these sites and verified the presence of juvenile horseshoe crabs by field surveys. Nearly all respondents reported an overall depletion in horseshoe crab populations from these 45 sites, which they attributed mainly to unsustainable fishing practices. Respondents who reported having seen horseshoe crab mating pairs on shores were mostly older people, which may suggest a considerable reduction in horseshoe crabs coming to the shores to spawn in recent years. The mean daily harvest of adult T. tridentatus offshore, as indicated by fishers, has declined from c. 50–1,000 in the 1990s to 0–30 individuals during 2011–2016. Our Wisdom of Crowds approach, supported by confirmatory field surveys, is a cost-effective method for assessing the population status of horseshoe crabs, and the level of threat they face. Similar approaches with other species are likely to be particularly valuable in the Asia–Pacific region, where well-structured population monitoring is largely unaffordable.

Socio‐demographic drivers and public perceptions of consumption and conservation of Asian horseshoe crabs in northern Beibu Gulf, China

“…Threats vary for individual species and among geographic populations, but all three Asian species are vulnerable to habitat degradation by coastal reclamation and development (Hsieh & Chen, 2015;Seino, Uda, Tsuchiya, & Tsuchiya, 2003). Tachypleus tridentatus populations are often subject to over-exploitation for food and Tachypleus amoebocyte lysate (TAL) production (Gauvry, 2015;Liao et al, 2019). Similar to other aquatic living fossils, such as nautilus and sturgeon, the depletion of horseshoe crab resources is exacerbated by their slow growth rate and the time thaht they take to reach maturity (Hu, Kwan, Wang, Cheung, & Shin, 2015).…”

“…Asian horseshoe crabs, particularly tri‐spine horseshoe crab Tachypleus tridentatus and coastal horseshoe crab Tachypleus gigas , are regarded as a source of food and traditional medicine in China and Southeast Asia (Faridah et al, ; Liao et al, ; Shin, Li, & Cheung, ). In many parts of the world's oceans Asian horseshoe crab populations are in decline (Hsieh & Chen, ; Kwan, Hsieh, Cheung, & Shin, ; Nelson et al, ; Weng et al, ).…”

Nursery habitat for Asian horseshoe crabs along the northern Beibu Gulf, China: Implications for conservation management under baseline gaps

“…Despite the fact that Beibu Gulf has widely been cited as the most suitable habitat for T. tridentatus (Brockmann & Smith, ; Sekiguchi & Shuster, ), the baseline population data are very limited. Based on the preliminary results from fisherman questionnaire surveys (Liao, Hsieh, et al, ), the first indication of nursery habitat distribution along the northern Beibu Gulf shoreline was provided, and 14 and 10 active nursery grounds for T. tridentatus and C. rotundicauda , respectively were identified through a programme of systematic sampling. Our findings support the claim that Beibu Gulf is the most suitable habitat for T. tridentatus , as six out of 14 nursery grounds in the northern Beibu Gulf had higher population densities (> 2.0 individuals/100 m 2 , Table ) than recorded in Hong Kong (Kwan et al, ; Lee & Morton, ).…”

“…The potential distribution of nursery shores for Asian horseshoe crabs was identified based on the previous fishermen interviews (Liao, Hsieh, et al, ) and scattered reports from the area (Chen et al, ; Hu et al, , ). Eighteen sandy mudflats located near three coastal cities, Fangchenggang, Qinzhou, Beihai, were visited in the spring and summer (April–September) of 2018 (Figure ).…”

“…Similar to many living fossils, these species exhibit slow growth, low dispersal rates, long life span, small home range and delayed reproductive development (Hu, Kwan, Wang, Cheung, & Shin, ; Kwan, Shin, & Cheung, ; Sekiguchi, ). These life‐history characteristics render them vulnerable to habitat degradation (Nelson et al, ; Tripathy, Sivakumar, Sajan, Satyaranjan, & Choudhury, ), habitat loss (Hsieh & Chen, ; Lee & Morton, ), and over‐exploitation for human consumption and bleeding (Fu et al, ; Liao, Hsieh, et al, ; Shin, Li, & Cheung, ). Li, Xie, and Kwan () estimated that at least 100,000 pairs of tri‐spine horseshoe crabs, Tachypleus tridentatus , are bled annually to support endotoxin contamination tests of injectable drugs as specified in the Chinese Pharmacopeia.…”