-To evaluate the population structure of Ucides cordatus in the Caeté estuary, crabs were sampled bimonthly over 13 months in three Rhizophora mangle forest stands that differed in their accessibility and fishing history. Additionally, sex-and size composition of the commercial catch and catch per unit of effort (CPUE -the number of crabs captured per fisherman per day) were monitored between 1997 and 2003. Average and maximum crab sizes (carapace width, CW) from all three sampling sites combined were 6.1 cm and 8.8 cm in males, respectively, and 5.5 and 7.3 cm in females. Crabs were largest at the site that had been reportedly less exploited in the past. The overall sex ratio was skewed towards males (53−62%). Egg carrying females were only encountered during the rainy season. Mean crab abundance and biomass was 1.7 specimens m −2 and 142 g m −2 fresh mass. Only large males were commercially harvested (98% ≥ 6.5 cm CW). Their biomass was 53 g m −2 and the Caeté estuary yields an annual production of 1200 t of these large specimens. This is approximately the quantity that is currently being harvested. CPUE was similar in 1997 and 1998, then decreased by 15% until 2000 and stabilized for the rest of the study period. Mean capture size (cm CW) ranged between 7.2 ± 0.5 and 7.5 ± 0.2 and was above the size of 50% (and even 100%) male maturity and the legal minimum capture size. There is no evidence that the Caeté crab population is overfished, despite over 30 years of de facto open access exploitation. Apparently, the selectivity of fishermen and consumers for large male crabs as well as the local artisanal capture techniques are key factors in preventing an overfishing of the Caeté crab population until today. Our results suggest that the economic and social sustainability of this fishery will be affected well before the biological one, which should be considered in the recently proposed coastal co-management plan for the region.
Key words:Mangrove crab / Ucides cordatus / Biomass / Sex ratio / Artisanal fisheries / CPUE / Management / Brazil Résumé -Structure de la population, composition des captures et CPUE du crabe de mangrove Ucides cordatus (Ocypodidae) capturé artisalement dans l'estuaire du Caeté, nord Brésil : signes de surexploitation ? Pour évaluer la structure de la population de Ucides cordatus dans l'estuaire du Caeté, ces crabes ont été échantillonnés tous les deux mois, sur une période de 13 mois, au niveau de trois sites de la mangrove à Rhizophora mangle qui diffèrent par leur accessibilité et leur historique de pêche. De plus, la composition (sexe et taille) des captures commerciales et celle par unité d'effort (CPUE -nombre de crabes capturés par pêcheur et par jour) ont été suivies entre 1997 et 2003. La taille moyenne et la taille maximale des crabes (largeur de la carapace, CW) de l'ensemble des 3 sites échantillonnés étaient de 6,1 et 8,8 cm pour les mâles, respectivement, et 5,5 et 7,3 cm pour les femelles. Les crabes étaient plus grands dans le site qui avait été moins exploité pa...
Epibenthic community structure, somatic production and energy flow were studied in the Caeté mangrove estuary in North Brazil on for 3 representative strata: high intertidal forest (F), small creeks in the forest (SC) and open mudbanks of large intertidal creeks (LC). Seven decapod crustaceans and 1 gastropod accounted for > 95% of total epifaunal biomass, with highest values in the forest followed by large and small creeks (228.2, 103.6 and 69.7 kJ m -2 respectively). The leafconsuming crab Ucides cordatus was clearly dominant in the forest, followed by the fiddler crabs Uca rapax and U. vocator. The large creek stratum was strongly dominated by the fiddler crab U. maracoani, while in the small creek 4 species (Uca cumulanta, U. maracoani, Pachygrapsus gracilis and Eurytium limosum) contributed similar quantities to total biomass. Per area somatic production (P) and respiration (R) was highest in the large creek, followed by the forest and small creek stratum. Based on the contribution of each stratum, total biomass (332.8 kJ m ) were estimated for the whole area. While the herbivorous feeding guild with U. cordatus was the most prominent in terms of biomass (75% of the total), the detritivorous fiddler crabs and P. gracilis clearly dominated in terms of respiration and somatic production (60 and 90% respectively). Carnivores (Eurytium limosum and Thais coronata) contributed < 2% to the epibenthic energy budget. A system picture emerges whereby energy flow is strongly dominated by herbivorous and detritivorous species. Both guilds probably promote mangrove primary production by (1) conserving nutrients in the system, (2) enhancing nutrient remineralization, and (3) oxygenizing the soil through their burrowing and feeding activities. A resulting positive feedback loop between mangroves, crabs and bacteria could explain the very high mangrove productivity and the high efficiency with which mangrove primary production is assimilated by the crabs (almost 15%).
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