Wisdom of Crowds reveals decline of Asian horseshoe crabs in Beibu Gulf, China Y ONGYAN L IAO,HWEY-LIAN H SIEH,SHUQING X U ,QIUPING Z HONG J UAN L EI,MINGZHONG L IANG,HUAIYI F ANG,LILI X U ,WUYING L IN X IAOBO X IAO,CHANG-PO C HEN,SIU G IN C HEUNG and B ILLY K. Y. KWAN Abstract Population decline among Asian horseshoe crabs in Supplementary material for this article can be found at Asia is increasingly reported, but knowledge of their popula- https://doi.org/./SX tion and ecological status in China is limited. We conducted community interviews in fishing villages around Beibu Gulf in Guangxi, China, to collect distribution information about the potential spawning/nursery grounds of Tachypleus Introduction tridentatus and Carcinoscorpius rotundicauda,andanyimmi- ecording changes in population status and identifying nent threats to their populations. Based on the results from anthropogenic factors responsible for species declines respondents we identified potential spawning/nursery R are fundamental for evaluating potential risks to biodiver- grounds distributed widely along the shores of Beibu Gulf. We sity and developing effective conservation management ac- visited of these sites and verified the presence of juvenile tions (Segan et al., ; Turvey et al., ; Bland et al., ). horseshoe crabs by field surveys. Nearly all respondents re- However, it can be difficult to obtain direct information on ported an overall depletion in horseshoe crab populations such parameters for species of conservation concern, par- from these sites, which they attributed mainly to unsustain- ticularly in geographical regions that have large human po- able fishing practices. Respondents who reported having seen pulations but little focus on formal scientific research or horseshoe crab mating pairs on shores were mostly older peo- monitoring of exploitation (Turvey et al., ). One such ple, which may suggest a considerable reduction in horseshoe case is the limited population research conducted on the crabs coming to the shores to spawn in recent years. The mean Chinese horseshoe crab Tachypleus tridentatus and man- daily harvest of adult T. tridentatus offshore, as indicated by grove horseshoe crab Carcinoscorpius rotundicauda in fishers, has declined from c. –, in the sto– China, despite China being largely responsible for driving individuals during –. Our Wisdom of Crowds the recent decline in horseshoe crab populations across approach, supported by confirmatory field surveys, is a Asia (Liao & Li, ; Weng et al., ; Gauvry, ). cost-effective method for assessing the population status of Tachypleus tridentatus occurs in the Seto Inland Sea of horseshoe crabs, and the level of threat they face. Similar ap- Japan, along the coast of China, and southwards to Borneo proaches with other species are likely to be particularly valu- and Sumatra in Indonesia, whereas C. rotundicauda is com- able in the Asia–Pacific region, where well-structured monly recorded in Indonesia, Malaysia, Singapore, the population monitoring is largely unaffordable. Philippines, Thailand, Cambodia, Vietnam and the Bay of Keywords Beibu Gulf, Carcinoscorpius rotundicauda,data Bengal in India (Sekiguchi, ). Horseshoe crabs are eco- deficient, horseshoe crabs, local ecological knowledge, mat- logically important in coastal ecosystems, serving as both ing pairs, Tachypleus tridentatus prey and predators, hosts for epibionts, and bioturbators for sediment–water nutrient exchanges (Botton et al., ; Botton, ). They also have high commercial value in YONGYAN LIAO* and BILLY K. Y. KWAN* (Corresponding author) Guangxi Key the manufacture of Tachypleus amoebocyte lysate, which is Laboratory of Beibu Gulf Marine Biodiversity Conservation, Qinzhou used in the testing of bacterial contamination in biomedical ’ University, People s Republic of China. E-mail [email protected] products (Walls et al., ; Gauvry, ). Despite being HWEY-LIAN HSIEH and CHANG-PO CHEN Biodiversity Research Center, Academia listed as Key Protected Aquatic Wildlife in four provinces Sinica, Taipei, Taiwan of China, T. tridentatus populations are heavily exploited SHUQING XU,QIUPING ZHONG,JUAN LEI,MINGZHONG LIANG,HUAIYI FANG and LILI to meet the increasingly high demands for Tachypleus amoe- XU Ocean College of Qinzhou University, People’s Republic of China bocyte lysate production and local food consumption (Liao WUYING LIN and XIAOBO XIAO Guangxi Biodiversity Research and Conservation Association, People’s Republic of China et al., ; Hong, ; Gauvry, ). Other factors contrib- uting to the depletion of horseshoe crab populations include SIU GIN CHEUNG Department of Biology and Chemistry, City University of Hong Kong, Hong Kong the destruction of their spawning shores as a result of coastal *Also at: Ocean College of Qinzhou University, People’s Republic of China reclamation, and marine pollution, as reported in Taiwan Received April . Revision requested May . (Hsieh & Chen, ), Hong Kong (Kwan et al., ) and Accepted July . First published online November . Japan (Seino et al., ). Carcinoscorpius rotundicauda Oryx, 2019, 53(2), 222–229 © 2017 Fauna & Flora International doi:10.1017/S003060531700117X Downloaded from https://www.cambridge.org/core. IP address: 170.106.33.19, on 30 Sep 2021 at 22:56:36, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S003060531700117X Wisdom of Crowds 223 populations in Hong Kong and Singapore are also decreas- towns around the three coastal cities (Fangchenggang, ing, mainly as a result of the loss of mangrove and mudflat Qinzhou and Beihai) along Beibu Gulf in Guangxi habitats (Shin et al., ; Cartwright-Taylor et al., ). Zhuang Autonomous Region, China (Table ). Beibu Gulf Tachypleus tridentatus and C. rotundicauda are currently is a semi-closed gulf located in the northern South China categorized as Data Deficient on the IUCN Red List Sea between China and Vietnam. The Gulf is km wide (WCMC, a,b), but based on the available evidence it at its widest and has a total area of , km (Chen et al., is likely that their populations will decline further because ). It has extensive estuarine ecosystems, with consider- their protection is a low priority for local governments able freshwater input from seven major rivers (Fangcheng, (Bland et al., ). In general, public awareness of the con- Qin, Dafeng, Nanliu, Red, Beilun, Changhua; Chen et al., servation of marine invertebrates is low (Cardoso et al., ). The rivers carry a significant load of nutrients from ). There is an urgent need for up-to-date information the land, which are essential for phytoplankton growth, on the distribution and population trends of Asian horse- which in turn supports the rich biodiversity and productive shoe crabs in China, and the threats they face, to protect fisheries in the northern South China Sea (Yu & Mu, ). remaining populations across their distribution range. To Both T. tridentatus and C. rotundicauda are recorded fre- this end, a broad approach that facilitates rapid, inexpensive quently in mangrove-dominated estuaries with patchy sea- and wide-scale collection of population data must be devel- grass beds and extensive sandy mudflats along the coastline oped. An important means of addressing information gaps of Beibu Gulf (Hu et al., ; Chen et al., ). In general, regarding species conservation and management, especially horseshoe crabs require three types of coastal habitats dur- in data-poor situations, is the collection of local knowledge ing their entire life cycle: adults nest on open, sandy beaches (Segan et al., ; Nash et al., ; Pan et al., ). This near the high water mark or along the edge of mangrove for- so-called Wisdom of Crowds technique is based on a mech- ests, juveniles forage and grow within the intertidal zones of anism that aggregates knowledge of a large sample popula- the same shores or their adjacent flats, and subadults and tion to generate quantitative estimates and spatial reasoning adults inhabit shallow subtidal areas (Chen et al., ; (Whitmore, ). Although the application of this method Smith et al., ). During the spawning season local people is relatively new, the merits of the approach, including its encounter adult C. rotundicauda mating pairs in amplexus independence, diversity of opinion, decentralization and burrowing in the mud along the edges of mangrove forests. aggregation, are recognized as of value for informing natural Mating pairs of T. tridentatus are occasionally entangled in resource management and conservation (Surowiecki, ; fishing nets cast along the coastline to harvest fish when the Arlinghaus & Krause, ). Previous studies have found tide recedes. that fishers’ perceptions about population trends matched scientific data reasonably well in some circumstances (Rochet et al., ; Daw et al., ; Arlinghaus & Krause, Methods ). In the case of Asian horseshoe crabs, local community members, especially fishers, may be able to report the histor- The villages and towns were chosen for the interviews be- ical and recent status of a species as well as underlying dri- cause sightings of horseshoe crabs on the beaches nearby vers of species decline (sensu Ainsworth et al., ). had been reported in the grey literature. Respondents were We conducted a study in three coastal cities along Beibu intercepted at random as the survey party walked through Gulf in south-western China to obtain data on the potential each village. We aimed to survey people of both sexes and distribution of spawning/nursery