Environmental perception of gatherers of the crab 'caranguejo-uçá' (Ucides cordatus, Decapoda, Brachyura) affecting their collection attitudes.

Abstract

Mangrove forests are productive ecosystems found along the coastal zones of Brazil, providing several profitable resources such as timber, medicinal products, natural dye, fish, crustaceans, and molluscs. For the littoral dwellers of Northeast Brazil, the Brachyura crabs are a major economic resource. The main species they commercialize are the 'goiamum' (Cardisoma guanhumi), 'siris' (Callinectes spp), and the land crab 'caranguejo-uca' (Ucides cordatus). The land crab is the most exploited species, and of most relevance for people living in the surrounding mangrove areas in the State of Paraiba [1-3]. U. cordatus lives in an individual burrow ca. 1 m deep, situated under mangrove trees. Adult crabs have few predators, notably the crab-eating racoon (Procyon cancrivorous), monkeys, and hawks [4]. Despite this, a high predation pressure on U. cordatus is exerted by humans who harvest this species for food [5]. In the Northeast Region of Brazil, the exploitation of U. cordatus holds particular socio-economic importance since it involves many local residents, who benefit from both direct and indirect employment [2,3]. Crab gatherers have observed that the natural stock of U. cordatus has decreased alarmingly since 1998, when an unexpected crab mass-mortality event occurred in the mangrove habitats of the Paraiban littoral [3]. The subsequent low crab abundance created social problems in the surroundings of those mangrove areas and seriously affected the economic welfare of poor people who depend upon crab gathering for their livelihoods. The need for research on the exploitation of mangrove ecosystems and on U. cordatus in particular was emphasized by Maneschy [6], who also suggested the need to study the socio-economics of crab collecting, which has recently experienced an increase in production demand. The life of gatherers is intimately linked to ecological processes and cycles, and their daily involvement with the exploitation of other natural resources will likely help them to develop harvesting strategies for maximizing the crab catch efficiency. An understanding of the ecology of U. cordatus by local gatherers is an important component of the process of exploitation [2,6]. In recent years, researchers have emphasized the importance of traditional knowledge amongst fishermen. They have also emphasized the potential role that traditional fishing practices can play in the development and implementation of sustainable fishery management in the modern world [7-9]. Human communities which rely directly on their natural resources for subsistence, often have a detailed understanding of their local environment [10-12]. The economic, social, and cultural activities of such people often depend upon local environmental goods and services [13]. Ecologists and environmental managers have generally disregarded the possibilities of learning from the traditional human communities [14]. However, a recent acknowledgment of their relevance has led to an intensification of studies on traditional knowledge [14-18]. In Brazil alone, Diegues [19] listed 868 relevant publications on traditional human populations, of which nearly 80% were published over the last 20 years, and mainly in the last decade. Traditional knowledge may help in the establishment of management plans aimed at the sustainable exploitation of natural resources [2,3]. Nordi [20] observed that the government environmental organization controlling the capture of U. cordatus does not consider local human knowledge of the ecology of the species, a fact that possibly explains the poor effectiveness of the regulations governing the exploitation of this resource. U. cordatus individuals are caught manually or by the use of some tools which allow easier access to them. In most of Brazilian States professional crab gatherers are male [21]. During normal harvest procedures gatherers select crabs with respect to both sex and size. In particular, male crabs are preferred due to their higher flesh yield [22]. Gatherers have developed the ability for distinguishing the sex of crabs as inferred from the track the animal leaves close to burrow openings, as well as from the size of burrow entrances. This perception is important since it directly influences the capture process since large male crabs are preferred due to their higher commercial value. The aim of the present work is to evaluate the ability of gatherers to discriminate the sex and size of crabs, and the importance of this ability on the development of successful harvest strategies. It is also intended here to evaluate the implications of this perception for establishing measures aimed at the conservation and management of U. cordatus.