International Horseshoe Crab Day
By: Wwf Hk
Tags: Mudflats, Marine Conservation, Horseshoe Crab, Nature, Hong Kong

by Thomas Gomersall

At the prompting of the IUCN Horseshoe Crab Specialist Group, the very first International Horseshoe Crab Day will be held on 20 June 2020. The aim is to generate greater awareness and conservation effort for these ancient creatures, which have existed virtually unchanged since the time of the dinosaurs and are important ecosystem engineers and predators of small organisms in modern intertidal environments (Fong et al, 2005).

Greater conservation efforts are certainly needed in Hong Kong, where two species of horseshoe crab (Tachypleus tridentatus and Carcinoscorpius rotundicauda) that were once common here have declined drastically since the 1990s (Shin et al, 2009; Pang, 2020). Coastal development has destroyed breeding beaches (Kwan et al, 2016, 2018) and the ones that remain are popular sites for recreational activities like clam digging, which reduces prey availability and harms horseshoe crab eggs and juveniles. Horseshoe crabs are also overharvested for food and Buddhist ‘mercy releases (Shin et al, 2009). The remaining populations in Hong Kong are now small, isolated, vulnerable and showing little signs of growth (Kwan et al, 2016). Yet shockingly, they are not protected under the Wild Animals Protection Ordinance (Pang, 2020).

Photo credit: WWF-Hong Kong

To mark the first International Horseshoe Crab Day on Saturday, a WWF team will visit Shui Hau to conduct research on horseshoe crabs living there, where it has been working to protect the species most notably through the ECF Sustainable Shui Hau Project.

WWF-Hong Kong has been working to protect local horseshoe crabs, most notably through the ECF Sustainable Shui Hau Project. From 2018 to 2019, the project mapped the distribution of both horseshoe crabs and clam digging in Shui Hau Wan — an important spawning and nursery site on Lantau — and found that areas with moderate-to-high densities of horseshoe crabs were at risk of disturbance from high- intensity clam digging and walkers, respectively. The project also found that clam-digging led to significant declines in the population, size and species diversity of clams, threatening a potentially important food source for horseshoe crabs.

To reduce some of these impacts, WWF teamed up with the Shui Hau community to create a code of conduct for clam digging, encouraging visitors to use smaller equipment and a clam gauge so they can dig for clams less destructively and know how big clams have to be before they are allowed to harvest them. From this summer onwards, WWF will also enact a series of experimental conservation measures, including encouraging clam diggers to avoid sensitive habitats (particularly ones frequented by horseshoe crabs), to only collect as many clams as they need, and to release smaller ones to allow the population to recover. WWF will closely monitor the effectiveness of these measures.

“We are piloting these measures to see if there are really any improvements in ecology and clam-digging behaviour,” says Lydia Pang, Project Manager for Oceans Conservation for WWF-Hong Kong. “By reducing the spatial overlapping of clam digging and horseshoe crabs, we hope we can reduce the threats to them.”

Photo credit: Kelvin Yuen

Changing the behaviour of clam diggers in one area can only do so much, however. Effectively conserving horseshoe crabs in Hong Kong will require conserving more of their habitats and better legal protections. To this end, WWF has been lobbying the government to have Shui Hau and Ha Pak Nai — another important horseshoe crab breeding site — designated as marine protected areas (MPAs) as part of its initiative to have at least 30 per cent of Hong Kong’s waters protected by 2030. It is also lobbying for a review of the Wild Animals Protection Ordinance or other relevant ordinances to adequately protect marine species under conservation concern, to make it illegal to harm, harvest, disturb or own horseshoe crabs and other marine wildlife.

Photo credit: Thomas Gomersall

Additionally, the overharvesting of horseshoe crabs needs to be curbed. Between 2004 and 2005 alone, 1,023 individuals were caught in Hong Kong and mainland Chinese waters, with around two-thirds of them sold in Hong Kong fish markets and seafood restaurants. It is also estimated that around 45 per cent of the horseshoe crabs sold per month in Hong Kong are fished from local waters (Shin et al, 2009).

WWF aims to launch new conservation campaigns to fade out sales of horseshoe crabs. In the meantime, members of the public should report to WWF any restaurants and seafood stalls that sell them. WWF will then estimate the current sales and formulate further conservation actions in collaboration with restaurants and seafood stalls.

Happy Horseshoe Crab Day!

References

· Fong, T.C.W., Lai V.C.S and H.T.H. Lui. 2005. Photographic Guide Series of Hong Kong Nature (2): Estuarine Organisms — Mangrove, Mudflat and Seagrass Bed. Jan KC Chan, HK Discovery Limited, Hong Kong. 65pp.

· Kwan, B.K.Y., Hsieh, H.L., Cheung, S.G. and P.K.S. Shin. 2016. Present population and habitat status of potentially threatened Asian horseshoe crabs Tachypleus tridentatus and Carcinoscorpius rotundicauda in Hong Kong: a proposal for marine protected areas. Biodiversity and Conservation, vol. 25(4): 673pp.–692pp.

· Kwan, B.K.Y., Chan, H.K. and S.G. Cheung. 2018. Habitat use of globally threatened juvenile Chinese horseshoe crab, Tachypleus tridentatus under the influence of simulated intertidal oyster culture structures in Hong Kong. Aquatic Conservation: Marine and Freshwater Ecosystems, vol. 28(1): 124pp.–132pp.

· Pang, L., interviewed by Thomas Gomersall, 2020, WWF-Hong Kong.

· Shin, P.K.S., Li, H.Y. and S.G. Cheung. 2009. Horseshoe crabs in Hong Kong: Current population status and human exploitation. In: Tanacredi J.T., Botton M.L. and D.R. Smith (ed) Biology and Conservation of Horseshoe Crabs. Springer, New York: 347pp.–360pp.