A single name for 4 species of swimming crabs

Swimming crabs were all thought to be part of one species until a 2010 study by researchers here showed otherwise.
Swimming crabs were all thought to be part of one species until a 2010 study by researchers here showed otherwise. ST PHOTO: ALICIA CHAN

The swimming crab is famous in Singapore and the region for being delicious when cooked in chilli or black pepper sauce, but it has also made a name for itself among the scientific community.

It was thought to be one species, Portunus pelagicus, until a 2010 study by local researcher Joelle Lai and crab expert Peter Ng found there were actually four species.

Because fisheries lump the species together, it is hard to tell if some are being over-harvested.

Data from the Food and Agriculture Organisation of the United Nations shows that 203,843 tonnes were fished from the wild in 2013.

The number is a collective figure for all four species, and does not indicate whether one species or another is at risk of over-harvesting.

Professor Ng, one of the scientists behind the discovery, said it takes time for new scientific names to be accepted by the community, used widely and then translated into policies.

Still, the scientific names for the four species seem to be gaining traction. In Australia, the name Portunus armatus is slowly coming into steady use, said Prof Ng, who heads the Lee Kong Chian Natural History Museum.

"The names tell us there are discrete genetic populations - these have different life cycles, growth rates, requirements and habits, so we need to manage them differently... A wrong name is not a good start to good management."

The four species are differentiated based on form and structure (such as colour patterns and the shape of the shell), genetic characteristics and location.

Portunus pelagicus is widely found throughout the Indo-West Pacific Ocean in South-east Asia and East Asia. Portunus segnis is native to the western Indian Ocean and extends to the east coast of South Africa. Portunus reticulatus can be found in the eastern Indian Ocean, while Portunus armatus has been found around most of Australia.

Audrey Tan

A version of this article appeared in the print edition of The Straits Times on December 14, 2015, with the headline 'A single name for 4 species of swimming crabs'. Print Edition | Subscribe