Development of improved mud crab culture systems in the Philippines and Australia

• Southeast Asian Fisheries Development Centre, Philippines
• Institute of Fisheries Policy and Devlopment Studies, Philippines
• Department of Primary Industries and Fisheries, Australia

At the start of this project Australia produced approximately 900 tonnes of mud crabs (Scylla spp.) annually. It was anticipated that production could double in six years to increase the value of the mud crab market to Australia by $10 million.

Due to the local and increasing international demand, a high priority was given to research on pond mud crab culture. Culturing of mud crabs with Gracilaria (a type of algae), prawns, milkfish or combinations of the three is widely practised in Southeast Asia. Polyculture (growing more than one species in the same environment) increases the overall production of the pond area and reportedly increases crab yield.

In a number of countries (including Australia) extensive areas of disused or under-utilised prawn ponds (30-40 thousand hectares in both the Philippines and Thailand) are available for alternative forms of aquaculture. But major barriers to successful commercial operations for mud crab culture existed, namely the lack of technology for the productions of juveniles and low pond yields (due mainly to cannibalism).

The objectives of this project were to optimise the conditions for the production of mud crabs at all stages of their development in a number of research trials, and to encourage mud crab farmers to adopt the improved methodologies.

The researchers modified or adapted existing technologies to suit the countries involved. The research took place at the Bribie Island Aquaculture Research Centre in Queensland, the Darwin Aquaculture Centre and the University of the Philippines in the Visayas (UPV).

Researchers had earlier identified the mud crab 'types' best suited to culture in a number of countries and developed strategies for nutritive enrichment of larval feeds, control of hatchery water quality and management of Scylla broodstock.

The main objectives of the project were:
to develop practical methods of managing broodstock that promoted consistent spawning and hatching of good quality larvae. (One female crab can produce 8 million eggs at each spawning, and existing rearing strategies yielded up to 20% survival to the crab stage.) This involved determining the optimum diet, water quality and systems for the mature females - in both Australia and the Philippines;
to optimise conditions for rearing larvae - through monitoring and optimising water quality, feeding and other important variables;
to determine a practical method which optimises yield from megalopae (larvae) and crab nursery cultures, looking at water quality, feeding, use of shelters and management;
to determine a practical method for optimising growth and yield of the maturing crabs by analysing diet, feeding, use of shelters, stocking densities and management;
to share the results of this research project, promote the sharing of information and examine areas requiring further research.

The project developed appropriate technology for hatchery and nursery production of crablets while also investigating increased pond productivity in the grow-out phase. A project extension enabled presentation of a training course in mud crab hatchery production. The course increased the human resource capacity in aquaculture.

In collaboration with mangrove researchers at SEAFDEC, in particular Dr Primavera, guidelines for the design of pens for farming crabs were developed. Building a range of pens in different types of mangrove forests, and using different techniques, led to a publication on pen culture for crabs.

This ACIAR-funded research was significant as it demonstrated that, if particular guidelines are followed, farming of mud crabs in pens in mangrove areas can be a benign, environmentally sustainable activity. When farmers were provided with small C2-C4 crablets (megalopae) and used hapa nets (fine meshed nets used to hold larval or juvenile stages of aquatic organisms) in the ponds as a preferred nursery technique, the growth of the crablets was rapid, there was relative conformity in size and a relatively high survival rate compared to stocking ponds with wild seedstock.

Economists attached to SEAFDEC developed economic models for both the hatchery/nursery and grow-out components of mud crabs, to complement the technological development. SEAFDEC and UPV produced their own publications on how to farm mud crabs for the Philippine industry, although SEAFDEC also used its publications in training courses which included overseas participants.

Using project research outcomes, the Bureau of Fisheries and Aquatic Resources (BFAR) continued its support for ongoing trials of mud crab culture in the Philippines, and both UPV and SEAFDEC offered training courses in mud crab hatchery production. Before the ACIAR-funded work on grow-out in ponds or in mangrove enclosures, advice given to farmers was based on pond grow-out systems for crabs caught in the wild. The technical advice to crab farmers on best techniques to rear crablets and how to grow-out mud crabs has changed as a result of the project, and the change was reflected in the handbooks for farmers that the project produced.

By the end of the project there appeared to have been only limited uptake of the hatchery technology, despite the advice on hatchery production that had become available through a number of publications. While several mud crab hatcheries were developed, and some farmers stocked and grew-out hatchery-produced crablets with good results, the vast majority of farmers still used wild fishery sourced stock. This is because hatchery production was limited and so wild-caught crablets were transported (even between islands) to farmers. It appeared that within the aquaculture industry in the Philippines, farmers had taken a 'wait and see' attitude - they were waiting for someone else to develop a hatchery and grow crabs from hatchery-produced crablets, rather than take the risk themselves.

Nevertheless, as a direct result of the ACIAR-funded research, several non-ACIAR funded projects were developed to prove the viability of different types of mud crab production. In total, these projects may be able to encourage the adoption of the improved mud crab hatchery and grow-out techniques by farmers. These projects were funded by the European Union (EU), German Technical Cooperation (GTZ), the Land Bank (a Philippines bank) and the Asian Development Bank. As well, a seafood dealer in the Philippines approached UPV staff to discuss a country-wide project to develop the mud crab industry.