Identification
Large mussel; length can exceed 15 cm. The shell is foot-shaped, very thick, and heavy. The anterior edge is rounded, the dorsal edge slopes straight, and the ventral edge is nearly straight, slightly concave in the middle. The outer surface of the shell has coarse growth lines and numerous deep radial grooves radiating from the umbo. These are arranged in a haphazard manner. The dorsal region has deep, regular oblique ridges interspersed with coarse protrusions. The shell surface is black, and the nacre is white.
Biology and Ecology
Lives on the sandy-muddy bottom of rivers in mountainous regions.
Distribution
- In Vietnam: Cao Bằng province (Bằng River).
- Worldwide: China (Guangxi – West River).
Value
Scientifically valuable. Used for food. Its thick shell is used as a nucleus for pearl cultivation and for handicrafts.
Status
A narrowly distributed endemic species. Before 1975, it was relatively common in the Bằng River. In the late 1980s and early 1990s, this species was heavily exploited, and the shells were sold to Chinese traders. Surveys in 2000 and 2001 did not yield any live specimens. Local people reported that they had not encountered this mussel for a long time. Due to overexploitation and possibly water pollution in the Bằng River (Cao Bằng town area), the distribution area has shrunk, estimated to be less than 100 km². The population of Trai cóc dày is estimated to have decreased by at least 80%. The estimated population is now fewer than 50 adult individuals.
Classification
CR (Critically Endangered)
A1c,d B1 D.
Conservation Measures
Included in the Vietnam Red Book and the list of species needing protection by the fisheries sector since before 1996. Recommended actions:
- Prohibit the exploitation of Trai cóc dày.
- Protect and restore the water quality of the Bằng River in the Cao Bằng town area.
- Limit sand mining on the Bằng River.
- Conduct research to supplement the population through artificial breeding.