An examination of the techniques used to capture mangrove crabs, Ucides cordatus, in the Mamanguape River estuary, northeastern Brazil, with implications for management
the Brazilian Federal Environmental Agency, considers the tangle-netting technique to have much greater environmental impacts than the traditional braceamento, and in 2003 prohibited its use as well as the use of the tamping technique in Brazil;
Boeger et al. (2005) stated that destruction of mangrove habitats, and diseases threaten local crab populations. Overfishing is also frequently suggested as a risk in many places, however for most Brazilian mangrove swamps available stock data are insufficient to confirm populational declines. crab stocks in the study area decreased significantly in 1998 due to significant die offs of U. cordatus (Alves and Nishida, 2002), probably due to the Lethargic Crab Disease (LCD) caused by the pathogenic fungus Exophiala cf psychrophila
prohibition of the tamping harvesting technique, but it is still used at the study site, as well as across the country;
two techniques are used at the study site for crab harvesting: tangle netting technique, and the now illegal tamping technique;
The Mamanguape River estuary (06° 430 0200 e 06° 510 5400 S X 35° 07' 46" e 34° 54' 04"W) is the second largest estuary in the northeastern Brazilian Paraíba State (16,400 ha), with a mangrove swamp covering 45.7 km2
the use of the tangle-netting technique involves the cutting of the roots of the mangrove species R. mangle
Given that tangle-netting results in greater harvesting pressure but lower selectivity compared to tamping, it may potentially be less sustainable. The tangle-netting technique is much less size selective than the tamping technique (22% versus 5% of total catch with illegal crab sizes), thus exercising a greater capture pressure on the crab pop- ulation. The lack of (i) data on the structure and resilience of the U. cordatus population in the Mamanguape River estuary, (ii) fish- ery stock assessments and (iii) knowledge of the magnitudes of secondary impacts caused by tangle-netting (pollution through discarded nets, cutting of the prop roots of R. mangle while setting the traps), does not yet allow to unambiguously evaluate whether the use of tangle-netting (and tamping) poses a real threat to the crab resources in the Mamanguape River estuary, and in many places elsewhere. Nonetheless, the perception of local crab har- vesters is that crab stocks have become reduced in the last 20 years, with decreasing average crab sizes suggesting overfishing. This perception of the crab harvesters, however, is based on long-term memories of harvesting stocks, memories that could well be exaggerated or otherwise inaccurate, and must be viewed with caution (Capistrano and Lopes, 2012).
Decreases in U. cordatus populations represent a threat to the sustainability of their harvesting, which can cause detrimental socio-economic impacts for thousands of people who depend on this resource for financial subsistence; Despite the fact that the tangle-net technique facilitates crab harvesting, the socio-economic status of these fishermen and their families remains very low. According to Alves et al. (2005), the almost complete economic dependence of these fishermen on harvesting U. cordatus results in significant environmental pressure on those animals and the mangrove ecosystem itself. The lack of alternative income options and the limited economic gains of crab harvesting make this activity barely economically sustainable;
Nascimento, D., Chaves Alves, Â., Nóbrega Alves, R., Duarte Barboza, R., Diele, K., & Mourão, J. (2016). An examination of the techniques used to capture mangrove crabs, Ucides cordatus , in the Mamanguape River estuary, northeastern Brazil, with implications for management. Ocean & Coastal Management, 130, 50-57. doi: 10.1016/j.ocecoaman.2016.05.010
All of the crab harvesters interviewed having more than 20 years of experience (n 1⁄4 34) stated they perceived that stocks of U. cordatus had become reduced over the last 20 years, together with average crab sizes. The harvesters using the tangle-netting technique captured 16.2% more crabs below legal minimum size (60 mm CW) than those using the tamping technique. The crab harvesters interviewed were unanimous in recognizing decreases in crab abundance and average crab size over the years, and in attributing this to increased harvesting pressure.
Historically, the profession of harvesting mangrove crabs, U. cordatus, in the Mamanguape River estuary was male- dominated. Capture activities are considered, at least locally, as excessively rigorous for women to perform, even using the tangle- net technique. As such, the energetic costs of harvesting activities, added to the physical risks involved, makes the participation of women much less frequent, and for fact absent in the study area.