OPCFHK’s first underwater automated acoustic telemetry system to study endangered horseshoe crabs
A momentous step forward in conservation efforts by documenting the movement and habitat usage of adult horseshoe crabs in Tung Chung Bay

(From the left) Prof Cheung Siu-gin, Associate Professor of the Department of Chemistry, City University of Hong Kong, Jaime Martin, Managing Director of Edrington Hong Kong and Macau, Howard Chuk, Foundation Director of Ocean Park Conservation Foundation, Hong Kong, and Kevin Laurie, IUCN Horseshoe Crab Specialist Group, Programme Officer, Steering Committee Member and Species Conservation Planning Focal Point. Today, the first batch of tagged adult horseshoe crabs were released in Tung Chung waters.

(Hong Kong, 21 February 2024) Hong Kong, known for its ecologically important horseshoe crab habitats, is home to two of four existing horseshoe crab species – the Mangrove horseshoe crab and the endangered Tri-spine horseshoe crab. Unfortunately, these incredible creatures are facing the threat of extinction due to human factors affecting their habitat and low survival rates of juvenile horseshoe crabs. The Ocean Park Conservation Foundation, Hong Kong (OPCFHK) has actively undertaken conservation efforts to enhance the breeding and survival rates of the local horseshoe crab population. Recognising the challenge of conducting ecological research under the sea where adult horseshoe crabs primarily reside, OPCFHK, with the generous support of Edrington Hong Kong, initiated the design and implementation of the first underwater automated acoustic telemetry system for a pilot tracking study of endangered horseshoe crabs in Hong Kong. The initiative started in October 2023 represents an important milestone in local horseshoe crab conservation.

Today, the research team released the initial batch of tagged adult horseshoe crabs in Tung Chung Bay and will continuously track and investigate their residency and movement, with a primary focus on studying crucial aspects such as breeding patterns. The study aims to provide more accurate evaluations of the habitat and breeding site requirements for local horseshoe crabs, offering valuable insights to support future ecological monitoring and habitat conservation efforts for these remarkable creatures.

Along the coastline of Tung Chung of Lantau Island, we can find one of the most significant grounds for adult horseshoe crabs inhabited to forage, breed and nurture their young. In a pioneering effort, the team introduced an underwater automated acoustic telemetry system, which had been successfully used in other countries like the United States and Japan to monitor adult horseshoe crab activities, for local research. Four strategically positioned acoustic receivers were deployed in the waters off Tung Chung Bay, Hau Hok Wan, and Sha Lo Wan for automated telemetry use, covering a monitoring area of approximately 3 square kilometres. Subsequently, each adult horseshoe crab, originally inhabiting the waters, was equipped with a transmitter specially designed for aquatic animal tracking prior to their release back into the sea. Upon entry of a tagged horseshoe crab into the detection range, relevant data such as presence time, location, and moving distance will be recorded.

Once the first phase of the survey concludes, the data will be retrieved from the underwater receivers, offering a comprehensive understanding of the movement range and patterns of the horseshoe crabs. Furthermore, the research team will analyse the collected environmental parameters, including water temperature and salinity, to further evaluate the habitat requirements of the local horseshoe crabs.

“The pioneering use of underwater automated acoustic-tracking telemetry for conduct tracking study on adult horseshoe crabs represents a significant advancement and holds immense importance, not only for the research work of OPCFHK but also for the broader objective of conserving the entire local horseshoe crab population. We strive to enhance our understanding of the ecology of local adult horseshoe crab and further develop effective conservation strategies based on scientific data, especially for adult horseshoe crabs. Alongside our 15-year Juvenile Horseshoe Crab Rearing Programme, the Juvenile Horseshoe Crab Population Survey and regular mudflat clean-ups, OPCFHK is devoted to raising public awareness about horseshoe crab conservation with advancing research, education and active public participation. Our commitment is to ensure the continuous breeding and survival of local horseshoe crabs in the wild,” said Howard Chuk, Foundation Director of OPCFHK.

With the generous support of our corporate partner, Edrington Hong Kong, OPCFHK has successfully initiated its inaugural automated acoustic-tracking telemetry study on local adult horseshoe crabs. “We at Edrington have always been deeply committed to environmental and ecological conservation and feel privileged to witness this crucial milestone in horseshoe crab conservation. Our ongoing collaboration with OPCFHK has been much anticipated and we look forward to raising awareness about this critical cause. Together, we strive to safeguard these ancient marine creatures and actively contribute to sustainable development and biodiversity preservation,” said Jaime Martin, Managing Director of Edrington Hong Kong and Macau.

The horseshoe crab, a species that has thrived on Earth for 475 million years, has a crucial evolutionary and biological value. Sadly, this ‘living fossil’ faces numerous threats in Hong Kong, including the loss of nursery beaches for juvenile horseshoe crabs, entanglement and mortality of adult horseshoe crabs in abandoned fishing nets and gear in the sea, as well as human exploitation. The local population of juvenile horseshoe crabs is estimated to be less than 10,000, while data on the adult population is inadequate, making it difficult to accurately estimate their numbers.

Since 2014, OPCFHK has conducted the juvenile horseshoe crab population survey, providing a continuous record of abundance, distribution, and population trends over time in four key local mudflats. The collected data has been shared with the Asian Horseshoe Crab Observation Network for further analysis. However, assessing the survival status of adult horseshoe crabs solely through mudflat surveys is challenging due to their preference for offshore habitats, with rare appearances onshore except during breeding and spawning seasons.

Research advisor Prof Cheung Siu-gin, Associate Professor of the Department of Chemistry at the City University of Hong Kong, brings valuable insights and technical support with his expertise in marine ecology and conservation as well as marine environmental studies. “During reproductive season, a female horseshoe crab can lay between 60,000 and 120,000 eggs in batches, but the chances of survival after their first molt are only one in ten thousand. Being one of the keystone species playing an important ecological role, protecting the habitat of horseshoe crabs, especially the spawning and hatching areas of the females, is essential for species conservation. With the use of acoustic-tracking telemetry, we can determine an accurate understanding of the reproductive behaviour of adult horseshoe crabs, such as breeding site preference. The collected data can also be utilised in assessing the impact of human activities on horseshoe crabs and their habitats, supporting sustainable natural resource management and conservation efforts," said Prof Cheung.

In addition to conducting scientific research for horseshoe crab conservation, OPCFHK actively promotes educational and community engagement programs. This includes the Juvenile Horseshoe Crab Rearing Programme, which involves participation from secondary school students and businesses in caring for artificially bred juvenile horseshoe crabs until they are mature enough to be released into the wild. As a member of the Asian Horseshoe Crab Observation Network, initiated by the IUCN SSC Horseshoe Crab Specialist Group in 2021, OPCFHK conducts regular monitoring activities. In parallel, OPCFHK organises mudflat cleaning events to remove marine debris that can entangle horseshoe crabs, reducing habitat pollution and rallying public support for conservation efforts.






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