Citizen science to support research on harvested Brazilian mangrove crabs

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Edinburgh Napier research in Brazil is helping to protect a cultural icon, influence policy and save livelihoods. Now a new citizen science smartphone app will take this one step beyond.

Ucides cordatus or mangrove crabs are revered in Brazil. Ornamented artefacts of their shells several thousand years old have been found and small coastal villages today celebrate them through beauty contests where entrants sport dresses made out of hundreds of crab legs. These crabs are the main source of income for thousands of low-income fishers who can catch them without the need for expensive boats or equipment. Edinburgh Napier’s Dr Karen Diele has been working with Brazilian colleagues to help secure the sustainability of the fishery of these economically and ecologically important mangrove crabs, and the many livelihoods depending on them.

“The guys who live from them are often very poor, illiterate, marginalised and they can’t afford costly fishing boats or nets. To catch these crabs, you don’t need a lot, so they are really important for poverty alleviation.

“These crabs live in the mangroves and Brazil has about 7,500 square metres of these highly productive intertidal forests. Under the canopy, the crabs dig two-metre-deep burrows. The fishers stick their arms or a hooked stick into the burrows to get them out, or they use tangle-nets. They have to protect their arms with gloves not because they are scared of the crabs, but because in the mud there are lots of sharp shells, and they can easily injure themselves - most fishers don't have any health insurance and can’t afford to lose income.”

Karen, from the School of Applied Sciences and St Abbs Marine Station, has been working with her Brazilian colleague Dr Anders Schmidt from the Federal University of Southern Bahia (UFSB) for a number of years to unravel the secret behind the species’ breeding pattern. These crabs mate around either full or new moon, but sometimes at both, and are very vulnerable to overexploitation at these times. Since the mating has been difficult to predict, as a result, capture bans are currently in place at both full and new moon in most areas in Brazil.

“That’s policy today. It prohibits catching at both full and new moon, even though the crabs mostly mate only at one of the two moons. Mate-searching crabs spend most of their time outside their deep burrows and it’s really easy to catch them then. Therefore there’s a risk of overfishing. But the fishers are furious because in most months one of the two bans is wrong and they’re not allowed to catch them even though they don’t mate. So the fishers lose income for no good reason. It’s not a very good solution.”

To help improve the placement of the capture bans and change policy, Karen and Anders have founded the researcher network REMAR, joining partners from nine institutions and study sites along the Brazilian coastline. The partners work with local fishers to find out what determines the crabs’ breeding patterns.

“These crabs are really clever," says Karen. "They pick days with big tides that are due when the sun and the moon are in a straight line. There is another cycle when the moon is closest to the earth. If that happens at new moon, then the new moon tides are bigger than the ones at full moon. It’s a complicated cycle but these little creatures have worked it out since the survival of their larvae depends on these big tides. We are pretty sure we can now predict for years to come whether these crabs will breed at new or at full moon, in any given year. But we need to prove it.”

Researchers from the REMAR network are now checking whether their predictions are correct. They are  expanding their surveys to obtain data from anywhere along the 7,000 km of Brazilian coastline. A new smartphone app (REMAR_CITIZEN) developed jointly with students and colleagues from the School of Computing at Edinburgh Napier will allow fishers and the general public to record where and when they’ve seen the crabs mating. All this data is automatically sent to a server at the School of Computing and analysed by Karen and her partners. The app will be launched in Brazil in November 2017.

“It’s real citizen science. The more people use the app and provide data, the easier it will be to showcase our results and convince decision makers to improve the crab fisheries policies. Biologically more adequate bans will mean that fishers and crab traders no longer lose income due to wrongly placed capture bans, and it would also reduce the costs for policing the bans.”

Researcher Network REMAR
Coordinators: Dr Karen Diele, Edinburgh Napier University / St Abbs Marine Station  & Dr Anders Schmidt, Universidade Federal do Sul da Bahia (UFSB)
Key collaborators:
Dr Marcio Ferreira, Universidade do Estado do Amapá  (UEAP)
MSc Andrei Cardoso, ICMBio, RESEX Marinha de Soure
Dr Darlan Simith, Universidade Federal do Pará (UFPA)
Dr José Mourão, Universidade Estadual da Paraíba (UEPB)
Dr Ana Rosa Araújo, Universidade Federal de Sergipe (UFS)
Dr Luiz Fernando, Universidade Federal do Espirito Santo (UFES)
Prof. Paulo Lana, Universidade Federal do Paraná (UFPR)
Dr Paulo Pagliosa, Universidade Federal de Santa Catarina (UFSC)

App development – REMAR_CITIZEN
Co-developed by Dr Karen Diele, Dr Anders Schmidt and colleagues from Edinburgh Napier School of Computing – Prof. Emma Hart, Dr Neil Urquhart,  Dr Simon Wells, Undergraduate students Michael Gauld and William Hutcheson;  with funding from Edinburgh Napier University and the Fisheries Science Forum of The Marine Alliance for Science and Technology for Scotland

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