What’s causing large-scale clam deaths in Ben Tre?
Ben Tre is a major supplier of white clam seeds for other parts of the Mekong Delta and elsewhere in Vietnam. Of Ben Tre’s 65-km coastline, 50 km are used for clam growing and its clams are a respected brand that offers clam collectors high profits. All eight of Ben Tre’s clam cooperatives are certified by the Marine Stewardship Council. However, according to local government officials, over the last three years there have been increasing episodes of clam death.
For people living in Ben Tre’s three coastal districts of Binh Dai, Ba Tri, and Thanh Phu, clam collection has been both profitable and low risk. Little capital is required because the clam seeds are sourced from the mudflats. But recent visits have revealed a growing concern among local people about the impact of what they perceive as increasingly erratic weather conditions.
The Thanh Loi Clam Cooperative in Thanh Phu District manages 400 hectares of clams and has more than 500 members including 312 who are officially defined as poor. According to Nguyen Van Xoan, head of the cooperative, 80% of the clams died in March and April 2011. He blamed this on unusually high temperatures during the hot season and higher than average salinity. This would be consistent with climate change models, which point to higher peak temperatures in the Mekong Delta. “To move forward, the management board needs to select seeds more carefully, reduce the stocking density, and monitor water quality and especially water temperature more strictly”, Xoan explained. The cooperative already gets technical support from the Provincial Clam Cooperatives Union, which provides annual training courses, but more help is needed, he said.
Large-scale clam deaths are also a headache in Ba Tri District according to local government staff who reported a 100% death rate in March and April 2011. They also blamed changing weather patterns and increased sea surface temperature and higher salinity. The An Thuy Clam Cooperative in Ba Tri is still suffering because it now lacks the clam seeds to sustain future harvests.
Ben Tre’s Department of Agriculture and Rural Development has sent seed samples to the Research Institute for Aquaculture 2 in HCMC, Ca Mau Aquaculture Research Sub Institute, Research Institute for Aquaculture 3 in Nha Trang, and the Nha Trang Institute of Oceanography to investigate the causes of the clam deaths. But so far the department has received no response.
The impacts of climate change on clams and other bivalves has been recognized in some scientific studies. (http://www.iucn.org/about/union/secretariat/offices/asia/regional_activities/building_coastal_resilience/sect_resources/). Higher sea surface temperatures result in reduced fertilization, size, and abnormal larvae leading to reduction in growth rates and yield. Diseases and parasites may also increase with a rise in temperature. Clam production has made a major contribution to raising incomes and reducing poverty in the coastal areas of the Mekong Delta. But the sector faces a new and serious threat. The recent clam dies offs are an early warning that as the climate changes, communities and local government will need to adapt. This is likely to involve diversifying local livelihoods and moving away from such high dependence on a single sector.
Nguyen Thi Phuong Thanh, BCR Field Coordinator, IUCN Viet Nam, HCMC