Population status and fishery potential of the mangrove crab,Ucides cordatus(Linnaeus, 1763) in North-eastern Brazil

Abstract

Ucides cordatusis a semi-terrestrial crab and key species endemic to mangrove areas of eastern Americas. In North-eastern Brazil this crab holds a major socio-economic function for artisanal fisheries, as in the São Francisco River Estuary (10°30′27″S 36°23′45″W). Nevertheless, decreases in this species’ stock have been reported since 2000, requiring assessments of the crab population for conservation and management purposes. This study aims at assessing the population status and the fishery potential of this species in the mangroves of this estuary and suggests strategies for its fishery and conservation, according to the guidelines of the National Management Plan forU. cordatusSustainable Use. Six different sites established in 30 km2of mangroves were sampled, with the density ofU. cordatusburrows estimated to evaluate the population structure using the measure of burrow diameters. Results show that the crab mean burrow size was 56.82 (±12.2) mm and that the medium-size crabs (40–70 mm) are the most abundant. The total mean crab density was 1.2 crabs m−2, from which the density of crabs in commercial size (0.85 ± 0.55 crabs m−2) was significantly higher than those in non-commercial size (0.35 ± 0.21 burrow m−2). These mangroves showed a high potential for the crab fishery, with an immediate extractive potential (IEP) of 71.2% and future extractive potential (FEP) of 28.8%. Nevertheless, a lower crab density, probably due to high crab mortality, mangrove deforestation for shrimp farming and high fishery pressure, is a limiting factor for local fishery. We conclude that mangrove areas more appropriate forU. cordatusfishery (extractive areas) show higher mean crab size, IEP and density of commercial crabs, wherein a fixed exploitation rate or/and a fixed escapement rule should be considered. Exclusion areas, intended for the conservation, show lower values of these population parameters and higher FEP, wherein the fishery should be prohibited. These management strategies should also be considered in other Brazilian mangrove areas showing similar crab population structure, thus contributing to the National Management Plan forU. cordatusSustainable Use.

Are Crab-collectors in Mangroves of Northern Brazil (PA) Optimal Foragers?

“…Diele et al (2005) had determined a mean density of 1.7 m − 2 , with an average carapace width of 66 mm for male (commercially relevant) crabs, about 10 years earlier. A similar density of 1.2 U. cordatus per m 2 was described for the estuary of the São Francisco River (NE Brazil) by Santos et al (2018). Much higher densities of 6 m − 2 were found at the Coroa do Sapo Island of São Paulo state (Pinheiro et al 2018).…”

“…Much higher densities of 6 m − 2 were found at the Coroa do Sapo Island of São Paulo state (Pinheiro et al 2018). Santos et al (2018) distinguished between crabs of commercially valuable size (based on burrow openings > 51 mm, representing a carapace width of > 60 mm; ≥65 mm carapace width, according to Diele et al 2005), reaching a density of 0.8 m − 2 , and those of smaller size, reaching only 0.4 ind. m − 2 .…”

A pesca nos manguezais no Estuário do Rio São Francisco: uma abordagem sócio-ecológica com ênfase no caranguejo Ucides cordatus (Linnaeus, 1763)

“…In turn, the small crabs occur in the margin of the mangroves or where the vegetation is not dense, which they call as a "thin mangrove" (Figure 2b). Corroborating with these answers, in our posterior study carried out in the mangroves of the study area (Santos et al, 2014b), we found that large and small crabs can occur in the same area of a mangrove, but large crabs are more frequently in areas dominated by Rhizophora mangle, and the smaller in areas with the occurrence of Laguncularia racemosa. Additionally, , in a study taken place in the North of Brazil reported that, in general, big crabs dominate the areas with Rhizophora mangle, corroborating with part of the information gave by the fishermen.…”

Spatial Analysis of a Coastal Area for Conservation and Fishery of Mangrove Edible Crab (Ucides cordatus)

“…For the map of mangrove vegetation types the normalized difference vegetation index (NDVI) was calculated using CBERS-2B images. The maps of crab population parameters were produced based on field data of six different sites of mangroves (e.g., Santos et al, 2014b) and the social maps based on ethnoecological survey carried in villages of the study area (e.g., Santos et al, 2013). We do not consider aspects of the life cycle of this species because since 1990 there are laws of closure during the breading and capture of females are legally prohibited at any time of year.…”