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Blue Swimmer Crab Restocking Project in The Coastal Waters

Funding Agency : Department of Fisheries (DoF)

Blue swimmer crab (Portunus pelagicus), locally known as ketam renjung or ketam bunga, is an important coastal fishery species . Fishing of this crab is usually operated by just one or two artisanal fishers in small boats, either using trap (bubu) or fishing net. Blue swimmer crab is excellent in taste with their succulent sweet and juicy flesh, highly sought after by seafood lovers. However, due to anthropogenic stressors and over-fishing in some coastal waters, the landing of blue swimmer crab has decreased.

Adult blue swimmer crab (Portunus pelagicus) seen among seagrasses during low tide.

In order to compensate the lower landing, fishers started to harvest even the immature crabs, leading to a vicious cycle which eventually threaten their livelihood as the crab population declines. I-AQUAS has established the blue swimmer crab seed production technology since 2018. However, demand for blue swimmer crab farming remains low as grow-out culture technology is still in the research phase.

Young crablet taking shelter on seagrass blade

In 2019, the Department of Fisheries Malaysia (DoF) started working with I-AQUAS to look into the needs for blue swimmer crab restocking programs. DoF was keen to improve the livelihood of artisanal fishers through periodical release of crablets into their natural habitats. Through this restocking effort, DoF wishes to assist the recovery of natural stock of the blue swimmer crab. After essential sites were identified, RM50,000 grant for the first year was given to I-AQUAS for crablet production. Millions of crablets have been given to DoF, which were released at the designated sites along the coastal areas.

Juvenile crab feeding on muddy bottom, their coloration blends well with the environment

Mature crab broodstocks were trapped at Port Dickson waters and brought back to I-AQUAS hatchery for conditioning. It usually took two weeks after hatched before the larvae settled as crablets. To ensure the higher survival rate of these crablets, I-AQUAS raised them further for a week or two before crablets were brought to the designated sites to be released into their natural habitats.

Crablets raised in I-AQUAS ready to be released

In the wild, the survival of crablets is highly dependent on the health of seagrass beds. Seagrass beds are important habitat for crablets, providing shelter and nursery ground with plenty of zooplankton to fulfil their nutritional needs. The restocking effort could assist natural population recovery but would not be as effective without healthy seagrass beds and awareness among fishers . Determining NO-TAKE crabs such as those below certain size measured by carapace width and the berried females are as important to ensure the sustainability of blue swimmer crab yield.

I-AQUAS together with DoF will continue to play our roles to ensure the sustainability of Malaysian fisheries.