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Farmed

Soft-shell mud crab of Indo-Pacific

Scylla serrata

Common Name(s)

mud crab; Indo-Pacific swamp crab, Mangrove crab, Giant mangrove crab

High

At least one of the environmental risk criteria has been scored high risk, and this is having a significant impact on the sustainability of the operation.

Indonesian

Kepiting-bakau besar

Vietnamese

Cua bùn

Cantonese

'Gur Yuen Ching Hai' (鋸緣青蟹), ‘Ching Hai' (青蟹)

Date of Assessments

November 2021 (Peer reviewed September and December 2022)

Peer Reviewer

Dr. Mojibar Rahman, Bangladesh Agricultural University

Eddy Nurcahyono, Balai Besar Perikanan Budidaya Air Payau Jepara (BBPBAP Jepara)

Assessment Organisation

The University of Hong Kong

SEASONAL AVAILABILITY

J
F
M
A
M
J
J
A
S
O
N
D

Overview

  • Scylla serrata, commonly known as Indo-Pacific swamp crab or mud crab, is found inhabiting mangroves and soft substrates in shallow or intertidal waters within the Indo-West Pacific region.
  • The aquaculture industry of S. serrata began in the 1970s in South East Asia and started to gain increasing popularity in 1990s.
  • FAO Fishstat reported nearly 133,000 tonnes of S. serrata production through aquaculture in 2019, with 54% from Vietnam, 30% from Indonesia and 16% from the Philippines.
  • Though official numbers are not reported, China is the largest producer of cultured S. serrata. Both Bangladesh and Thailand appear to be minor producers.
  • Although technology and knowledge regarding hatchery produced seed stock has been developed in certain countries such as Indonesia, the majority of the industries are still relying on wild-caught seeds for S. errata aquaculture.

Individual rearing

  • The most common system is individual rearing, in which intact crabs are held in perforated plastic boxes, with several boxes being positioned in pontoons or floating platforms.
  • The number of days to harvest and quantity per harvest in each crop cycle in soft-shell crab aquaculture is somewhat fluctuating in nature, as the harvest depends on different environmental variables and an unpredictable crab moulting stage. Therefore, the crop cycle generally has a large range of 25-45 days.
  • The term soft-shell crab refers to the physiological state of any crab that has just undergone moulting to replace their old hard exoskeleton with a new, slightly larger, hydrated and decalcified soft exoskeleton, which is the stage of crabs with the highest market value.
  • As the exoskeleton would become very firm in about 3 hours, the short harvest timeframe makes soft-shell crab farming a labour-intensive aquaculture industry.

  • The latin species name
  • Evidence of the country of origin, name and location of the farm
  • Evidence that the farm is compliant with national regulations
  • Evidence that production is controlled in a way that minimises impact on the wider marine environment (i.e. there is local planning, water quality testing etc.)
  • Evidence of where the seed originates
  • Evidence that the seed used on the farm has come from sustainable sources
  • Evidence of where the feed originates
  • Evidence that the feed used on the farm has come from sustainable sources
  • Evidence that the farm does not use any banned medicines / chemicals
  • Evidence that there is a plan / procedure in place to manage animal husbandry

AQUACULTURE IMPROVEMENT PROJECT

The Government organisation, BBPBAP Jepara, is engaging in various mud crab programmes including cultivation, hatchery, restocking and pond maintenance to push for a more sustainable mud crab fishery

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COUNTRY SPECIFIC RISK ASSESSMENTS

  • The soft-shell form of S. serrata production in Bangladesh can be considered to be a high risk.
  • The S. serrata farming is totally dependent on wild seed supply.
  • Most soft-shell crab farms took place in coastal water bodies that were formerly used for shrimp farming, which could have inherited similar environmental risks such as mass mangrove forest destruction and raised numerous environmental concerns. The implementation of National Aquaculture Development Strategy and Action Plan of Bangladesh 2013–2020 is also not evaluated.
  • Most farmers use low value trash fish such as minced tilapia and/or snail meat that are sourced from local coastal areas as feed, often feeding at 5-10 percent body weight daily on an as-needed basis, yet the sustainability of the trash fish fishery in Bangladesh is not evaluated, including the impact of coastal trawling with small mesh size to the ecosystem.
  • Potential impacts of infectious pathogens on intensive mud crab farming are not well established.
  • There is no standard crab culture manual available in the country. Several problems including improper salinity and water quality deterioration have been reported in S. errata farming.

 

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  • The soft-shell form of S. serrata production in Indonesia can be considered to be a high risk.
  • The productions rely solely on seedlings from capturing S. serrata in mangrove forests since hatchery-based reproduction has still not reached high quantities. Signs of S. serrata resource depletion was found, as both number and body size of S. serrata harvested have decreased in the last 15-20 years.
  • Water quality monitoring and records on feed used in the soft shell crab cultivation are kept. Yet the impact of waste generated by soft shell crab ponds has not been well documented.
  • Trash fish is used as the main feeding source for soft-shell crab farming in Indonesia, yet the sustainability of the trash fish fishery in Indonesia is not evaluated, including the impact of coastal trawling with small mesh size to the ecosystem.
  • Most aquaculture ponds are adjacent to mangrove or coastal areas, where semi-closed systems are practised in a way that floating cages with crabs inside are placed in aquaculture ponds built on land, filled with water pumped from an adjacent brackish or salt water source and returned to the environment after use. The indoor crab boxes set-up with a recirculating water system (RAS) has been reported in Indonesia, yet the degree of prevalence of such systems is not reported.
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  • The soft-shell form of S. serrata production in Thailand can be considered to be a high risk.
  • Most soft-shell crab ponds were converted from shrimp ponds that were close to mangrove forests in Ranong District. The newly established soft-shell crab farms may had inherited similar environmental risks posed by shrimp farms, including mangrove destruction and saltwater intrusion.
  • Trash fish is used to feed S. serrata being reared in individual cages, yet the sustainability of the trash fish fishery in Thailand is not evaluated, including the impact of coastal trawling with small mesh size to the ecosystem.
  • Although hatchery production has been achieved, large-scale adoption by private farmers is yet to occur. The high demand of juvenile crabs for soft-shell crab production had led to crab imports from other countries such as Myanmar and Cambodia.
  • General information suggests that the wild population has been significantly depleted in both abundance and size throughout its natural resource range (Kosuge, 2001) due to increased harvesting effort by the growing population, indiscrimination in harvesting, overexploitation and habitat loss (Lewis et al., 2008), overfishing throughout their distribution (Shelley, 2016), overall environmental degradation, and climate change as well.
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