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Researchers conducting horseshoe crab population surveys utilising unmanned aerial systems and artificial intelligence technology in the Ha Pak Nai mudflat. (From the left) Dr Zhang Jihan, Postdoctoral Research Fellow, Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong; Prof Ben Chen, Professor and Department Chairman, Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong; Dr Judy Wan, Conservation and Community Partnerships Manager of the Ocean Park Conservation Foundation, Hong Kong; Prof Cheung Siu-gin, Associate Professor of the Department of Chemistry, City University of Hong Kong; and Mr Kevin Laurie, IUCN Horseshoe Crab Specialist Group, Programme Officer, Steering Committee Member and Species Conservation Planning Focal Point.
(Hong Kong, 19 June 2025) June 20 marks the sixth International Horseshoe Crab Day, celebrating a species that has existed on Earth for over 470 million years. As one of the oldest surviving species, horseshoe crabs hold significant evolutionary and biological value. The Ocean Park Conservation Foundation, Hong Kong (OPCFHK) has been conducting horseshoe crab population surveys in Hong Kong since 2014, covering various breeding and nursery mudflats. Last year, in collaboration with the Department of Mechanical and Automation Engineering at The Chinese University of Hong Kong (CUHK) and the Department of Chemistry at City University of Hong Kong (CityU), a two-year pilot programme using autonomous unmanned aerial systems (UASs) and artificial intelligence (AI) technology for horseshoe crab population surveys at the Ha Pak Nai mudflat was commenced. With continuous testing and enhancements, the system's accuracy in identifying juvenile horseshoe crabs has reached over 90%, significantly improving the effectiveness of future population surveys. The team plans to expand the system’s application to other local horseshoe crab habitats, including Shui Hau Wan on Lantau Island.
“In 2021, the Steering Committee for the International Union for Conservation of Nature (IUCN)’s Horseshoe Crab Species Specialist Group set up the Asian Horseshoe Crab Observation Network Programme. This initiative involves conservation organisations and research teams from mainland China and Hong Kong collaborating on horseshoe crab population surveys across 25 monitoring stations. OPCFHK is responsible for data collection at the monitoring stations in Ha Pak Nai, Sha Tau Kok, Luk Keng and Tung Chung Bay. Through collaborating with CUHK and CityU on the pilot programme, the team has not only gathered more accurate data on horseshoe crabs but has also developed a systematic image annotation process and sophisticated AI algorithms. We plan to extend this technology to more locations, including Shui Hau Wan on Lantau Island,” said Howard Chuk, Foundation Director of OPCFHK. “Shui Hau Wan boasts diverse habitats and is recognised as a breeding and nursery ground for Tachypleus tridentatus and Carcinoscorpius rotundicauda (mangrove horseshoe crab). By conducting systematic research on the local horseshoe crab population there, we hope to provide more data to inform conservation efforts in formulating more targeted measures in safeguarding this endangered species."
Addressing the pain points with advanced technologies
Current horseshoe crab population surveys primarily involve researchers counting visible horseshoe crabs on mudflats. This method is constrained by natural factors such as limited tidal activity windows and adverse geographic conditions. Moreover, survey results can be affected by the species’ cryptic colouration and the unpredictable activity patterns of juvenile horseshoe crabs. Furthermore, researchers walking through the mudflats can cause a certain degree of disturbance to their habitats.
The pilot programme employs UASs to collect field data and incorporates innovative image data annotation and morphological characteristic extraction technologies. Guided by conservation experts, the research team developed a systematic data annotation process specifically designed for the burrowing behaviours and morphology of juvenile horseshoe crabs. They then built and trained AI algorithms to detect and identify horseshoe crabs from the images collected by drones. Utilising advanced image segmentation models, the team further refined and classified the collected images based on the species’ morphological features, such as the length, width, and continuity of their unique crawling tracks. This approach enables the AI system to filter out various environmental interferences, significantly improving the efficiency of the surveys by achieving an identification accuracy of over 90%.
Researchers can predefine survey scopes and drone routes, as well as operate multiple drones concurrently. This not only saves manpower and time but also expands the number of survey spots. For instance, the survey area at the Ha Pak Nai mudflat measures approximately 150 metres by 1,000 metres. In the past, it was necessary to divide this area into separate zones, requiring a team of at least four researchers to record the number of horseshoe crabs at the same time. Each survey would take about one to two hours. After adopting the UASs, only one researcher is needed for each survey, while the real-time data collection duration could be reduced to just around 30 minutes. Furthermore, challenging-to-access areas like coastal mangrove strands can be covered, yielding more valuable data on the distribution of local horseshoe crab populations.
Prof Cheung Siu-gin, Associate Professor of the Department of Chemistry at CityU is an expert in marine ecology, conservation, and marine environmental studies. He has been actively involved in local horseshoe crab research. As a subject advisor and co-investigator of the project, he stated: “Through this pilot programme, we are combining domain expertise with AI deep learning technology. By analysing the collected data, including elevation variations, temperature changes, and chlorophyll concentration, we can parameterise horseshoe crab habitat maps. This process enables us to establish correlations between habitat suitability and various environmental factors, facilitating the development of targeted strategies for habitat improvement or restoration. As a result, we can create a more conducive environment for the growth and reproduction of horseshoe crabs, enabling for a proactive approach to drive population expansion. We will continue our long-term research, enhancing the precision of the AI system through field learning and expanding the horseshoe crab image database. This will enable us to analyse the status of local horseshoe crabs from multiple dimensions, including seasonal population trends and long-term habitat usage patterns, thereby improving the effectiveness of conservation efforts."
The UASs and AI technology used in the project were developed by the Department of Mechanical and Automation Engineering at CUHK. The pilot programme is funded by the Environment and Conservation Fund, and its technical team is led by Prof Ben Chen, Professor and Department Chairman and Prof Chen Xi, Research Assistant Professor. Prof Ben Chen pointed out: “This interdisciplinary project is highly challenging because our drone-based ground environment mapping solution primarily operates at an altitude of about 60 metres. However, due to the small size of juvenile horseshoe crabs, we need to lower the detection altitude to around 4 metres during search missions, which drastically reduces coverage efficiency. To address this issue, we successfully combined habitat suitability mapping with prioritised flight path planning to optimise drone deployment, achieving a balance between data resolution and survey scale for sustainable, large-scale monitoring. After a year of testing and enhancements, we believe this system also holds broad applicability for large-scale ecological monitoring across terrestrial and marine ecosystems, such as forests and coral reefs, allowing locally developed technology to create a greater impact on environmental conservation.”
Joint forces to safeguard endangered horseshoe crabs
In addition to conducting population surveys, OPCFHK is actively collaborating with various sectors in society to build a comprehensive network for horseshoe crab protection. With funding support from the Lantau Conservation Fund, OPCFHK partnered with residents and community groups in Lantau to launch the “Safeguarding the Lantau Intertidal Mudflat Biodiversity” initiative in July 2024. This initiative aims to raise awareness among the public, particularly Lantau residents, fishermen, and tourism operators, about the ecological value of intertidal mudflat ecosystems through education and community engagement. The project recruits local residents to become “Lantau Mudflat Wardens” and provides them with training. These wardens will perform regular patrols, documenting issues such as “ghost nets”, marine animal entanglement and marine debris. They support OPCFHK in clean-up operations, working together to safeguard Lantau’s natural resources. OPCFHK also partnered with the Caritas Chan Chun Ha Field Studies Centre to publish a picture book designed for primary school students. The book, titled “Old Horseshoe Crab Tells Stories: Continuing the Miracle of Life”, introduces the importance and value of horseshoe crabs.
Furthermore, the “Horseshoe Crab Rearing Programme”, a long-standing collaboration between OPCFHK and CityU, has entered its 16th year. This programme encourages secondary school students and corporations to participate in caring for artificially bred juvenile horseshoe crabs. Since 2009, over 370 schools and corporations, with more than 7,000 participants, have supported the programme. They have successfully released 2,000 horseshoe crabs back into the nature, contributed to the population restoration. Additionally, OPCFHK regularly organises mudflat clean-up activities to remove marine debris that could have entangled horseshoe crabs, reducing habitat pollution and rallying public support for conservation efforts.
To support the survival of local horseshoe crabs, OPCFHK urges the public to actively engage in conservation in their daily lives. This includes clearing mudflat litter to reduce the impact of environmental pollution on horseshoe crab habitats, as well as avoiding the capture, disturbance, or purchase of wild horseshoe crabs to minimise human interference with natural ecosystems, thereby jointly protecting these “living fossils”.
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