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Biology

Life among crabs

Project leads to changes in the standards of management of this crustacean in the Southeast

EDUARDO CESARUçá, the crab on the Southern-Southeastern coastline: study corrects distortions and helps save the mangrove swamps EDUARDO CESAR

A pioneering project on the uçá (Ucides cordatus) or true crab is part of biological research – morphology, biometry, physiology and reproduction – using the knowledge acquired through communities traditionally devoted to the exploitation of this species that lives in mangrove swamps. The project lasted two years and provided crucial data – especially on the reproduction times, the reproductive potential, the embryology, growth and size in sexual maturity – for the preparation of more appropriate rules for sustainable exploitation. It also increased the chances of the rules being obeyed, as it tightened communication between the crab men (gatherers) and contributed to their needs being taken into account in the regulations.

“Biologists and inspectors were viewed with mistrust by the crab gatherers because they imposed bans and punishments. We were the first to want to learn about their difficulties and to listen to what they knew about the crabs”, says Marcelo Pinheiro, of the Applied Biology Department of the São Paulo State University (Unesp) at Jaboticabal, who coordinated the project.

The conclusions the study reached helped reformulate the ordinance issued by the Brazilian Institute for the Environment and Renewable Natural Resources (Ibama), which regulates the exploitation of crabs in the South and Southeast. The minimum size of crab that can be collected, for example, has risen from 5 to 6 centimeters shell length. This is the size of the uçá crab at an age when half the population of each sex reaches sexual maturity – and this only happens when they are three years old. This ensures that most of the animals are given the opportunity to reproduce.

In compensation, the defensive period – when gathering is banned – was shortened slightly, which benefits the gatherers. The 1998 ordinance was based on studies done in the Northeast, so that gathering the uçá crab was banned between September 1 and December 15. In the light of the new study, carried out in the town of Iguape, last year’s ordinance now bans gathering from October 1 to December 31 along the entire coastline from Rio de Janeiro to Santa Catarina. For this year, the period was shortened further, ending on December 20, and the regulation now also covers the coast of Espírito Santo.

“As gathering females with eggs is banned the whole year, we observed that this would be the most important period for protecting the species’ reproduction in the Southeast and South, because it is when the nuptial change occurs and it is the main mating period”, explains Pinheiro. The changes were made based on discussions between representatives of Ibama, the Forestry Police, fishermen, and the gatherers themselves. “When people take part in drafting a law, they are much more likely to obey it”, says the biologist.

In joint work with the Research and Fishing Extension Center of the Southeastern and Southern Regions (Cepsul), and with Ibama, the research group produced a guidance manual in comics, to make local people aware of the importance both of the species – whose raising in captivity is not feasible due to its slow growth – and the mangrove swamps where it lives, a breeding ground for fish and other crustaceans, such as shrimps.

Population threatened
The work is timely, since, because of its size and abundance, the uçá is one of two species of crab of economic interest that lives only in mangrove swamps – the other is guaiamum – land blue crab (Cardisoma guanhumi), typical of the Northeast. The uçá, which usually lives in the low-lying mangrove swamps – where they remain under water most of the time -, is sought after for its flesh, which feeds many families in the surrounding areas, as well as for the chitin in its shell, used in preparing filters, anticoagulants, chemical adhesives and even cosmetics.

With the increased exploitation, however, the abundance and average size of the uçá has been reduced in some regions. This affects not just those that earn their livelihoods from gathering the crabs, but it also damages the mangrove swamp itself, since the uça plays an important part in the food chain of this ecosystem, which helps process the falling leaves, incorporating their nutrients into the soil.

And the mangrove swamps are essential to the balance of neighboring ecosystems. Their vegetation prevents the banks of the estuaries from silting up and their organic richness increases marine productivity. In addition, many economically important fish and marine crustaceans use the mangrove swamps as a feeding and reproducing ground and as a refuge, guaranteeing protection for the development of their larvae. Hence, the disappearance of a mangrove swamp also threatens fishing.

For all these reasons, Ibama has already expressed concern over the scarcity of data on the Southeastern and Southern regions which would help draft efficient protection regulation for the uçá. The few studies available were done in the Northeast and the crabs’ reproduction period varies according to the latitude. In view of this, Ibama recommended the survey proposal to FAPESP.

The funding covered a motor boat, a refrigerator, scales, an oven, an air conditioned chamber, payment of the gatherers, and an item of equipment for the computer analysis of images, used in measuring more than 3,000 crabs. Around 150 uçás a month were gathered, in the mangrove swamps of the Iguape region, in the Southern coast. They were divided into males, egg-bearing females, and non egg-bearing females.

Each was weighed and measured – across the cephalothorax (part of the shell), the abdomen, the claw (known as the propod of the greater chelapod) used for hunting and fighting for females and in the male abdominal appendices (gonopods), analogous with the penis. This enabled changes in the growth rate of these structures to be identified and to propose limits as to the size of males and females according to four stages of development: young, pre-pubescent, young adult, and adult.

Reproduction
As with other crabs, the male uçá has two penes, and the female has two vaginas. The gonads – testicles and ovaries – were examined to determine the degree of maturity and filling of the two spermatheca – sacs where the female keeps spermatozoids for at least two months after copulation, until the ovaries are mature enough to be impregnated.

The copulation period is related to the phenomenon of the walkabout, which takes place chiefly in December and January at full and new moons. During the walkabout, most of the crabs leave their burrows and perambulate on the mangrove swamp’s sediment, where the males fight over the females. The data also suggest that copulation also takes place in October, following the “nuptial change” – when the uçá’s shell turns a bright sky blue – and at this time of the year, walkabouts are not common.

The study observed that in the Iguape there are only egg-bearing females between December and March, a little before this happens in the Northeast. “As the law bans gathering egg-bearing females at any time, we recommended banning gathering during the main mating period, which is when the crab is most vulnerable”, explains the researcher. The eggs of around 60 egg-bearing females were counted and used in the study on embryo development, which disclosed eight distinct stages. Experiments carried out in the air-conditioned chamber showed that the ideal salinity for the development of the embryos is 15 parts per thousand.

Researching the period when there is the highest number of females with full spermatheca and of egg-bearing females, the study concluded that there is a period of at least two months between copulation and fecundation. Soon after fecundation, between 36,000 and 250,000 eggs are expelled to the abdomen where they adhere to the appendages that act as a sort of semi-open container, where the eggs are incubated for around 18 days, when kept at an average temperature of 27 degrees centigrade, then the larvae emerge from the eggs, are borne to the ocean by the outgoing tide and return to the mangrove swamps when they are close to the young stage.

One of the difficulties of farming the uçá is precisely controlling the various levels of salinity appropriate to each of the larvae’s stages. They also have specific food needs. Most never reach adulthood, but as part of the living plankton they play an important part in feeding mollusks and fish.

Three years
Around 50% of the uçás are sexually mature at 3 years of age, when the shell reaches around 5 centimeters long. It was decided to increase the minimum gathering size to 6 centimeters because of the species’ slower growth rate. The studies suggested that the uçás reach a maximum shell size of 9 centimeters and that they live up to 9.2 years in the case of males and 8.3 years for females.

“It is not worthwhile raising them commercially because there are other crustaceans that grow much faster, such as the siri crab (Callinectes sapidus), and this just increases the importance of sustainable handling to protect the species from predatory economic exploitation”, says Pinheiro. He also recalls that the initial idea for the study came precisely from the large number of inquiries he received from people interested in farming the uçá. In fact the coverage of the survey increased as the project went on.

Caiçara science
“We had to hire caiçaras (people living along the coast) to gather the crabs and we discovered that not only did we have a lot to learn about them but that we had to take the social factor into account in order to establish an efficient policy for protecting the species”. Hence, the idea arose of expanding the study. We interviewed randomly 43% of the Iguape gatherers enabling us to establish a socioeconomic profile of them.

Most (70.6%) did not complete primary school (grade 8)e and almost 12% never went to school at all. Most (88%) are men between 16 and 58 years old, with time in the job ranging from 6 months to 22 years. Three quarters of them essentially earn their living from gathering crabs. More than half are married or living with a partner, and they have an average of four children a couple. Monthly family income ranges from R$ 110 to R$ 1.000, with an average of R$ 400.

No Pity
Lesions and infections of the skin of the hands and arms – caused by abrasion from the countless roots intertwining in the soil of the mangrove swamps – are part of the day-to-day life of the gatherers. “If you are a crab gatherer you can’t afford to worry about your body”, says José Lourenço de Souza, 53, who has been in the business for 21 years. Known as Zeca-do-Caranguejo, he is the oldest and most experienced crab gatherer in Iguape. He has also worked as a farm laborer and in fishing, businesses he considers uncertain, while in the mangrove swamps, he says, he can “easily” collect 300 crabs a day.

Most of them (64%) pick the uçás directly with their hands, a method they call braceamento (arm work). But 36% admit to using traps – for example, a small net – which is banned because it does not distinguish small animals or egg-bearing females, both of which are readily identified by 85% of the gatherers.

Necessary cost
Although three quarters of the gatherers said they knew when gathering was banned, only a quarter answered correctly as to when this protection period was. Pinheiro considers it essential for the preservation of the uçá not just to inspect the gathering and to sponsor environmental education but also to arrange some form of income for gathers’ families to enable them to survive during the banning period: “Their position is very precarious. When they disobey the law, it may be a question of survival, just punishing them does not solve the problem”.

Based on the caiçaras’ empirical knowledge, the researcher set up an ethno-biological calendar listing what happens to the crabs each month – walkabout, releasing the larvae, shedding their shells and other situations.”To our surprise, we discovered that around 70% of the gatherers’ knowledge of the uçá was the same as the scientific data established in the survey”, says Pinheiro.

Milky crab
The perception the gatherers have of the life cycle, the morphology and the behavior of the uçá was surveyed, as were the changes the mangrove swamp ecosystem has undergone. They are fully aware of the deterioration of the mangrove swamp, the reduction of the crab population, and the size of the crabs as the years have gone by. The gatherers call the uçá the “milky crab” before it changes its shell, which takes place a little before mating. During this stage, the crab’s internal organs turn a characteristic milky color.

“This phenomenon occurs with a few semi-terrestrial and terrestrial crabs, mainly in environments with little calcium carbonate and magnesium, substances essential to strengthening the shell”, comments Pinheiro. For this reason, before swapping the old shell for a larger one, the crab dissolves and absorbs these substances into its blood stream to use in manufacturing the new shell. “The gatherers say that the milky crab is not good to eat because it is bitter, makes you dizzy, and gives you stomachache. It is true: I checked in medical books and this is indeed the effect of consuming large quantities of these substances”, reveals the researcher.

“We discovered many things with the gatherers”, agrees the biologist Ana Gláucia Fiscarelli, who was in charge of the ethno-biological part of the project. Many gatherers can distinguish between the burrows of males and females according to the tracks left at the entrance. With males the end of the small toes is hairy leaving a deeper more brushed track, while that of females is smooth”, points out Zeca-do-Caranguejo.

“We also learn to pick out the tracks of the raccoon, one of the mammals preying on the crab. The raccoon can remain seated, motionless, in front of the entrance to the burrow, waiting for the crab to come out”, says Gláucia. The survey showed, however, some gaps in the gatherers’ knowledge of certain important characteristics of the uçá.

Uçá II on the way
No gatherer, for example, identified the larvae, as a stage in the development of the crab. And nor did most of them know exactly when the banned gathering period was, or how the protection laws are established. “This shows the need for education on the biology and the handling of this resource, and its environment, and this will be one of the objectives of the Uçá II project, which is currently being prepared”, says Gláucia.

The study has already led to an illustrated manual for teaching inspectors and policemen how to recognize the uçá, to handle the animals apprehended and release them back into the mangrove swamps. A primer has also been produced in comics form, to create awareness in the shore dwellers of the importance of the mangrove swamps and of the uçá, and of how to conserve them. The idea arose when Pinheiro’s eight-year-old daughter came home from school crying because her school friends laughed when she told them that her father studied crabs.

“I saw that not even my daughter understood the importance of what I was doing, so I decided to prepare a booklet in language that anyone could understand”, says Pinheiro, who is looking for finance to be able to publish the book, the first working tool on environmental education the team intends to prepare.

The Project
Biology of the Uçá Crab (Ucides cordatus) on the Coastline of the State of São Paulo; Type Normal research support line; Coordinator Marcelo Antonio Amaro Pinheiro – Unesp at Jaboticabal; Investment R$ 67,850.00 and US$ 10,674.05

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