Survey to assess stock of mudcrab |12 September 2022

• SFA studies its potential for aquaculture

The Seychelles Fishing Authority has commissioned a one-year stock assessment of mudcrab to better understand the species, its population and abundance, and its potential for aquaculture, according to a top official.

When announcing the study during a press conference late last week, the head of the Aquaculture department, Aubrey Lesperance, said in the past the Seychelles Fishing Authority (SFA) had focused mainly on fish and not on other species living in a mangrove habitat like crabs. However, there had been numerous requests from people who wanted to know more about the species as well as breed mudcrabs as a business venture.

“We know there are some people who harvest mudcrabs, although not regularly, and these are sold to restaurants. We did a seafood survey in 2008, where mudcrabs featured on some menus and they were being sold up to R400, so they do have economic value,” he said.

Prior to the study, SFA had done research on mudcrab farming, the methods being used worldwide and the ideal habitats for its reproduction. These included south-east Asia where the type of farming is popular and successful, and closer to home, SFA officials observed what was being done in Kenya.

Mr Lesperance explained that their initial observation was that mangroves in Kenya were vast compared to those in Seychelles and the method used there include placing the crabs separately into small cages and allowing them to grow until they reach their full sizes, ready for consumption.

SFA conducted a small-scale trial prior to this assessment to see whether the method would apply in Seychelles and to see whether Seychelles mangroves will provide the environmental conditions required for the type of breeding.

According to Mr Lesperance the results were not positive.

“Our mangroves are small and sparse compared to Kenya’s and therefore does not protect the crabs from direct sunlight. We noticed they were not growing and started losing weight,” explained Mr Lesperance.

Another issue was the level of water, which is important for the crabs to thrive. Mr Lesperance said they observed that low salinity brought about by rainwater, stressed the mudcrabs and hindered their growth as well.

SFA is considering two methods. Firstly, aquaculture where they use brood stocks and male and female species reproduce in captivity until they reach their full sizes. The other method is ‘ranching’ where middle-sized crabs weighing between 100 to 200 grammes are kept in cages and fed fish until they reach the right size for consumption.

Mr Lesperance said the second method is unreliable as it has been successful only in south-east Asia, and not so in other countries. He said the study will shed more lights on the two methods and prove scientifically whether it can or cannot be done in Seychelles.

“If we allow ranching, will it mean catching all the mud crabs we see in the wild or should we depend on the reproduction method in aquaculture? If we allow mud crab farming to take place we need to decide if breeding will be done in the natural habitat or should we resort to a man-made environment thrive,” said Mr Lesperance

The stock assessment is being funded by SeyCCAT and will be conducted by Bee Ecological Consulting, with Gilberte Gendron as lead consultant.

She explained that the study will be done in two phases, the first one this month, will involve the participation of fishermen who were either involved with the business venture in the past or are presently catching mudcrabs either on a full-time basis or for leisure.

“They will be asked to fill in a questionnaire that will address questions that will include the techniques they are using, how regular they are doing this type of fishing and where are the areas they are setting the traps. These will be useful to SFA when it is coming up with its strategy,” explained Ms Gendron.

The questionnaires will be available online and the consultants will also be available for one on one meeting to help those who need assistance to fill out the forms.

The second component, in October, will involve the setting up of traps in mangrove areas, where according to Ms Gendron, mudcrabs will be caught, tagged and released into the wild.

She said the objective is to catch them again at a later date to see their development and growth, as the study will be done over a 12-month period.

“During that period we can get the scientific information such as how long it takes for them to grow, to change their shells, their distribution in the mangroves, their habitat and if there is a correlation between the presence of the crabs and the species of mangroves or vegetation in those areas,” said Ms Gendron.

Bee Ecological Consulting is calling on everyone not to tamper with their traps and to refrain from taking any tagged crabs they come across, as this would affect their data collection.

“Of course there is no law that prevents a person from catching a crab but in the event that you take one of the tagged crab, please ensure that you return the tag to us so that we’ll know which one has been captured,” she added.

Bee Ecological Consulting said it will be carrying out the surveys in marshes on the three main islands, Mahé, Praslin and La Digue, and possibly on Silhouette and other islands. The consultants have carried out a recce to better understand the types of vegetation there are and the areas exposed during high and low tide. However, according to Ms Gendron, they will be able to finalise the sites once they receive information from the questionnaires, which will help them to shortlist the areas ideal for the study.

SFA said the project will be done in two phases and the first phase, which includes consultancy fee, costs US $28,000. The second phase, which will include the purchasing of cages for the study, will be revealed later.

Patsy Canaya