DESCRIPTION OF MUD CRAB FISHING

Gear used to fish for juveniles

The techniques for collection of juvenile crabs were comprehensively reviewed in the seminar on mud crab trade and culture, conducted by the Bay of Bengal Programme (Angell, 1992). In particular details were provided for the Bay of Bengal (Sivasubramaniam and Angell, 1992), and countries attending the seminar (Cholik and Hanafi, 1992; Kathirvel and Srinivasagam, 1992; Khan and Alam, 1992; Ladra, 1992; Tookwinas, Srichantulk and Kanchannavasiste, 1992).

For juvenile and larger crabs, the gear used can include baited traps, lift nets or lines, together with hand held hooks, scoop nets, gillnets and fish corrals. For crab larvae and very small juvenile crabs, which are yet to settle, fine meshed push nets or drag nets can be used.
In the Philippines a small meshed net is mounted on a V-shaped bamboo frame and pushed across muddy substrates to collect juveniles, whilst for larger crabs a variety of traps are used with fish baits to attract the crabs. In Viet Nam juvenile crabs are collected from canals and coastal waters using a bottom seine net (Johnston and Keenan, 1999).

Statistics on juvenile collection

Whilst production figures on farmed mud crabs are available for most countries, there appear to be no official statistics on the collection of juvenile crabs. It has been estimated that juvenile (20–60 mm carapace width) S. paramamosain can be found at densities of over 1 000 ha-1 (Le Vay, Ut and Walton, 2007) in some locations where their commercial harvest is undertaken.

Post-harvest techniques

Juvenile crabs caught specifically for farming will typically be packed, without water, in boxes or bags and kept in a moist environment during transport, either to a middleman or farmer. Juvenile crabs can be transported in this manner successfully for several days without significant mortalities if properly packed.
If crabs of commercial harvest size are collected there are 3 main ways in which they are handled. Method one for hard shelled, “full” crabs is for the crabs to be tied to secure their limbs and packed into boxes or bags, kept moist and then transported to market, typically via an agent, or middleman. The vast majority of mud crabs are sold live. Method two is the fattening of “empty” or “soft” recently moulted mud crabs (Ladra, 1992; Liong, 1992; Rattanachote and Dangwatanakul, 1992). This can be regarded both as a post-harvest technique and as a specific type of aquaculture. In India, Patterson and Samuel (2005), described the success of a crab fattening project operated by a self-help women’s group. In the wild fishery approximately 7–10 percent of the catch on average was “empty” and would usually be discarded, but these crabs when fattened for 21–30 days to a “full” crab, increased in average value by over 200 percent (US$4.63 to US$9.53 per kg), making a good profit for the women's group. Method three is for smaller crabs in the range of 50–150 g. Such crabs can be held in individual containers and checked regularly to see if they have moulted. On moulting, whilst their shells are still soft, they are either chilled or frozen for the “soft shell” crab trade, a market segment rapidly gaining in popularity, particularly because soft shells fetch an even higher price per kilogram than do hard shell crabs.