Asymmetric outcomes:: assessing central aspects of the biological, economic and social sustainability of a mangrove crab fishery, Ucides cordatus (Ocypodidae), in North Brazil

Central aspects of the sustainability of a mangrove crab fishery in the Cacte estuary, Para, North Brazil, are assessed according to biological, economic and social criteria and based on a 5-year data series. Ucides cordatus is probably a keystone species in this mangrove ecosystem. Over half of rural coastal households depend on the crab for at least part of their income. The fishery shows seasonal and annual differences in terms of labour input, capture volumes and productivity. During the rainy season, more crab collectors work than during the dry season, although labour productivity is generally lower. A reason for this seemingly irrational producer behaviour is the lack of alternative income sources during this time of year. Labour productivity over the monitoring period decreased by 16%. Present crab fishery does not seem to endanger the U. cordatus population as a whole. Mostly mature old crabs, which have reproduced several times already, are captured. Females are not targeted due to lack of market demand. Nonetheless, males are slightly more abundant than females suggesting that the reproductive output of the crab stock is maintained at a sufficient level. Central for the economic and social sustainability of the fishery is crab collectors' purchasing power, which, between 1998 and 2001, fell by 20%. In 2001, the economic sustainability threshold was reached as crab collectors' incomes net of operational and investment costs fell to about the level of the official Brazilian minimum wage. This means that crab collection is now being undertaken at an income level which only just covers the regeneration of crab collectors' labour. At the same time, an ongoing erosion of social sustainability is reflected in territorial conflicts between crab collectors and in the incidence of alcoholism and reliance on child labour in crab collector households. Thus, the current fragility of economic sustainability and the undermining of social sustainability are accompanied by apparently undisturbed biological sustainability conditions. This highly asymmetric outcome is a challenge for transdisciplinary efforts to establish relevant fishery management priorities with the active participation of the centrally affected stakeholders. (C) 2004 Elsevier B.V. All rights reserved.