Horseshoe Crabs in Hong Kong: Current Population Status and Human Exploitation
An updated survey, using both random transect and walk-through search methods, at 17 shores in Hong Kong in summer and winter showed that juvenile horseshoe crabs (Tachypleus tridentatus and Carcinoscorpius rotundicauda) were significantly reduced by over 90% in density since 2002. Of the shores where juveniles were found, the highest density of T. tridenatus was 0.31 and lowest 0.08 ind 100 m–2. Juvenile C. rotundicauda was only found using the walk-through search method, with the highest record of 1.17 and lowest 0.17 ind hr–1 person–1. The mean prosomal width of juvenile T. tridentatus obtained from the walk-through survey varied from 2.6 to 5.5 cm, which corresponded to an age of 4–8 years old. A larger size range for C. rotundicauda was, however, noted, from 2.5 to 9.0 cm.
The degree of human exploitation of adult horseshoe crabs (T. tridentatus) in Hong Kong was estimated through interviewing 34 seafood restaurants, 150 fish sellers and fish handlers, and fishermen in two local fish wholesale markets over a 13-month study period. A total of 1,023 horseshoe crabs were caught in 2004–2005, with 72% from mainland Chinese waters. Apart from releasing back to sea, an average sale of 17 horseshoe crabs per month was estimated. While the sale of horseshoe crabs was low by comparison with other marine species of economic importance, human exploitation still contributes a potential threat and puts further pressure on the mature population of horseshoe crabs in Hong Kong due to their long maturity period and declining densities of the juveniles.
KeywordsTidal Level Horseshoe Crab Horizontal Transect Prosomal Width Horseshoe Crab Population
We would like to thank funding support from the Environment and Conservation Fund from the Hong Kong Special Administrative Region Government and Woo Wheelock Green Fund, Hong Kong. The presentation of this paper at the International Symposium on Science and Conservation of Horseshoe Crabs was supported by a travel grant from the Scientific Committee on Ocean Research, International Council of Science, USA.
- Chiu HMC, Morton B (1999a) The biology, distribution and status of horseshoe crabs, Tachypleus tridentatus and Carcinoscorpius rotundicauda (Arthropoda: Chelicerata) in Hong Kong: Recommendations for conservation and management. Final Report. The Swire Institute of Marine Science, The University of Hong KongGoogle Scholar
- Chiu HMC, Morton B (1999b) The distribution of horseshoe crabs (Tachypleus tridentatus and Carcinoscorpius rotundicauda) in Hong Kong. Asian Mar Biol 16:185–196Google Scholar
- Chiu HMC, Morton B (2003a) The status of horseshoe crabs in Hong Kong. In: Morton B (ed) Perspectives on Marine Environmental Change in Hong Kong and Southern China. Proceedings of the Hong Kong Workshops Reunion Conference on Perspectives on Marine environmental Change in Hong Kong and Southern China (1977–2001). Hong Kong University Press, Hong Kong, pp 743–758Google Scholar
- Itow T (1998) The pollution of coastal waters and malformations of horseshoe crab embryos. Bull Fac Educ Shizuoka Univ Nat Sci 48:15–33Google Scholar
- Mikkelsen T (1988) The Secret in the Blue Blood. Science Press, BeijingGoogle Scholar
- Morton B, Lee CNW (2003) The biology and ecology of juvenile horseshoe crabs along the northwestern coastline of the New Territories, Hong Kong: Prospects and recommendations for conservation. Final Report to China Light and Power Company Limited. The Swire Institute of Marine Science, The University of Hong Kong, Hong Kong, pp 91Google Scholar
- Morton B, Williams GA, Lee SY (1996) The benthic marine ecology of Hong Kong: a dwindling heritage. In: Coastal Infrastructure Development in Hong Kong. A Review. Proceedings of the Symposium on Hydraulics of Hong Kong Waters, Civil Engineering Office, Civil Engineering Department, Hong Kong Government, pp 233–267Google Scholar
- Sekiguchi K (1988) Biology of Horseshoe Crabs. Science House Co., Ltd., TokyoGoogle Scholar