- Fishing of blue swimming crabs in Thailand has historically exceeded sustainable levels, leading to a decline in both the number and size of crabs that fishers were catching.
- Understanding the urgency of recovering the crab population, fishers, government agencies, NGOs and the private sector have rolled out a series of initiatives to make the fishery more sustainable.
- These include seasonal bans on harvesting egg-carrying crabs, restrictions on trawling and certain kinds of fishing gear, and the establishment of crab banks, where egg-bearing females are nurtured, with their hatchlings later released into a secure marine site.
- Fishers and experts welcome the crab banks, but emphasize the need for a “sustainable holistic scheme,” given that a reliance on crab banks alone won’t rebuild blue swimming crab populations.
PHUM RIANG, Thailand — The sea is quiet except for the swish of the longtail boat cutting sharply through the waves. Fishermen Sutham Abmanee and Komsan Witan, from Phum Riang in Thailand’s Surat Thani province, set out at 7 a.m., just as they do every day. When they reach the right spot, Sutham starts to pull out the nets he’d set the night before. They’re strung with silvery sea bass, tiny golden starfish, and blue swimming crabs. The men expertly pluck them out, keeping the valuable catch and dropping the rest back into the ocean.
Blue swimming crabs (Portunus pelagicus), instantly recognizable by their long blue pincers (green-brown in females), are at the top of the “valuable” list. But they won’t all be sold. Sutham holds a crab upside down in the palm of his hand. A female, her underside is covered with a spongy, bright orange substance: eggs, millions and millions of eggs. “When they are this color we know that they will take a few days to hatch,” he says, gently placing the crab in a bucket of water. “We need to take her to the bank.”
Blue swimming crab populations in Thailand
Blue swimming crabs are found across Southeast Asia and the Pacific, and their meat is considered a delicacy in many parts of the world. But for the residents of Phum Riang, home to 400 small-scale fishermen, blue swimming crabs are more than a profitable catch — they’re at the core of the community’s livelihood and identity. The village is located within the area of Bandon Bay, which accounts for half of Thailand’s blue swimming crab production. Even residents who don’t fish for crabs are often involved in other stages of their production, such as processing or selling the meat.
In the 1990s and early 2000s, as international demand for crab meat grew, unsustainable fishing practices such as trawling proliferated. Total annual catches of blue swimming crab in Thailand reached a peak of 46,678 metric tons in 1998, far above the maximum sustainable yield. Fishers in Phum Riang began to notice a decline in the number and size of blue swimming crabs in the sea. Along with the crab population, their income was declining too.
Crab banks: A new solution
The need to protect blue swimming crabs, and the local fishing economy, was clear. In 2017, a Fishery Improvement Project (FIP), led by the Department of Fisheries, WWF, and private sector partners, was launched to support sustainable fishing practices. This included seasonal bans on harvesting egg-carrying crabs, and restrictions on trawling and certain kinds of fishing gear, such as traps with a mesh size smaller than 6.4 centimeters (2.5 inches). The plan also promoted an initiative dating back to 2007: the crab bank. Here, egg-carrying females are fed and protected until their eggs hatch. Once the offspring are strong enough, they’re released into the sea. Since its start, the crab bank model has expanded widely across Surat Thani province, with public facilities, NGOs, private groups and fishermen themselves setting up their own banks. There are now at least 15 crab banks in Surat Thani.
Funded by the municipal government, the Phum Riang Public Crab Bank is a modest building located by the shore, with white walls and a mural of two giant crabs in bright blue paint. Every morning and evening, manager Suepphong Khongkaeo places newly deposited crabs into one of the bank’s seven bubbling pools, and pours carefully measured solutions of feed, mostly rehydrated tiny crustaceans called artemia, into the water. The bank’s records show that between October 2023 and October 2024 it released 159,000 young crabs and millions of their larvae, known as zoeae, into the sea.
Zoea measure less than 1 millimeter (0.04 in) in length, and they go through several stages of development before becoming juvenile crabs. The later they’re released, the greater their chances of survival. But it can take more than a month for a zoea to become a young crab, and limited space and resources mean it’s not always possible to wait. “The feed is very expensive,” Suepphong says.
Viya Crab, a local company that produces tinned crab products, established its own crab bank 10 years ago. “We produce 1,000 tonnes of crab per year, so we believe that we should help to replenish the stock,” says deputy managing director Madena Laojaroen. “We release 1 million zoeae every day, but our experience suggests that the rate of survival for zoeae is around 0.01%. That’s why we are also releasing 10,000 young crabs per month.” At the young crab stage, the survival rate is 60%, Madena says.
Sutham also runs a small bank out of his own home, together with a group of other fishermen in the village. They take in at least 20 female crabs a week. “We also release the mother crab, so she can reproduce again,” Sutham says. This, he says, isn’t always common practice in other banks, as adult crabs are valuable. The fishermen received a donation from the private sector in the form of technical equipment at the initial stage, but currently they have no financial support and bear all the costs themselves. “For us, it’s simple,” he says. “If there are no crabs, we have no livelihood.”
Recent data clearly suggest that blue swimming crab populations have increased since the crab banks and other management measures were put in place. Based on the data, marine biologist Amonsak Sawusdee of Walailak University, who has decades of experience studying this species, says he’s confident that “crab bank activities effectively support the restoration of blue swimming crab populations.” But he adds that restocking alone isn’t enough; appropriate regulations and enforcement around fishing gear, and the creation of protected areas for spawning and juvenile crabs, are also essential to long-term sustainability.
A refuge for young crabs
For Somboon Siriraksophon, an expert in fisheries in Southeast Asia, the crab bank initiative raised a key question. “How can we know the zoea [or young] crabs that they release back to nature, to the sea, have survived? That is the problem,” he says. His solution: finding a suitable, protected area where juvenile crabs could be released. In 2018, the Southeast Asian Fisheries Development Center (SEAFDEC), the U.N. Environment Programme (UNEP) and the Global Environment Facility (GEF) collaborated with Thailand’s Department of Fisheries to establish a refugia site in Surat Thani’s Koh Sed Island, with Somboon as the project manager. This designated area, spanning 900 hectares (around 2,225 acres), restricts the use of certain fishing gear, creating a safe zone for releasing young crabs. The location was carefully chosen after months of consultation with the fishing community and extensive research about its ecological and geographical suitability.
Isabelle Vanderbeck, international waters task manager for UNEP, says the refugia model differs from traditional marine protected areas in that it focuses on “the joint management of fish life cycle — critical habitat and sustainable use — rather than on the prohibition of fishing.” By involving government, private sector groups, and small-scale fishermen like Sutham, this model aims for an “all of society approach,” in which all key stakeholders are invested in the sustainability of crab fishing. The model has been replicated for different at-risk species within Thailand as well as in several other countries in the region.
Challenges ahead
Despite the successes, some challenges remain. Some fishermen, including Sutham, have reported illegal fishing of young crabs in the refugia site. “The fishermen can monitor the area,” Somboon says, “but they don’t have the authority to prevent illegal fishing.” More support is needed from the Department of Fisheries on the enforcement front, he says. There are some suggestions that this is a broader issue. A 2023 report from Seafood Watch, a U.S.-based group that evaluates the sustainability of different species consumed as seafood, describes fishing regulations for blue swimming crabs in the Gulf of Thailand as “ineffective,” advising consumers to avoid the region’s crabs based on fishing mortality data and bycatch risks.
Ultimately, the conservation of marine species targeted by fisheries is an extremely complex task, influenced by myriad factors and players. Vanderbeck emphasizes the importance of a “sustainable holistic scheme” encompassing a range of initiatives such as crab banks, “which in and of themselves do not suffice for reverting the malpractices in fisheries.” Crab banks are certainly part of the solution, but a reliance on crab banks alone won’t rebuild blue swimming crab populations.
Back to the ocean
Later that day, Sutham grabs a couple of buckets from his community-run crab bank and, wearing a visor to shield against the fierce afternoon sun, boards his longtail boat with other fishermen and Theradej, his 10-year-old nephew. “He likes this part,” Sutham smiles.
A short ride brings them to the white sand and crystalline waters of Koh Sed. Sutham and Theradej gently pour the buckets’ contents onto the shore, releasing thousands of tiny zoeae and, finally, the young crabs. They each submerge a crab in the shallow waters of the shore. As they release their grip, the crabs quickly scuttle away, beneath the sand and into the ocean.
Banner image: Fisherman Komsan Witan carefully removes a blue swimming crab from his fishing net. Image by Ana Norman Bermúdez for Mongabay.
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Citations:
Jutagate, T., & Sawusdee, A. (2022). Catch composition and risk assessment of two fishing gears used in small-scale fisheries of Bandon Bay, the Gulf of Thailand. PeerJ, 10, e13878. doi:10.7717/peerj.13878
Kunsook, C., Gajaseni, N., & Paphavasit, N. (2014). A stock assessment of the blue swimming crab Portunus pelagicus (Linnaeus, 1758) for sustainable management in Kung Krabaen Bay, Gulf of Thailand. Tropical Life Sciences Research, 25(1), 41-59. Retrieved from https://ejournal.usm.my/tlsr/article/view/tlsr_vol25-no-1-2014_4
Nootmorn, P., Jindalikit, J., & Talawat, P. (2018). Sustainable management of blue swimming crab in Thailand. In SEAFDEC Technical Seminar 2018 (pp. 32-36). Training Department, Southeast Asian Fisheries Development Center. Retrieved from https://repository.seafdec.or.th/bitstream/handle/20.500.12067/1461/9_Praulai_%20blue%20swimming%20crab.pdf
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