Spatial and Temporal variations of mangrove fish assemblages in Martinique (French West Indies)

A study of the mangrove fish fauna in a bay of Martinique Island (French West Indies) was carried out at different seasons during two consecutive years. fishes were sampled with specific hoop-nets in the coastal areas at 8 stations.A total of 87 species was collected in the bay. Most individuals were represented by small-size specimens and juveniles. The overall species richness varied according to the stations and the sampling periods. The biomass and number of individuals were variable according to the location but remained stable in time. A factor correspondence analysis and a hierarchical clustering with median links were used to follow the evolution of the stations in space and time. Two types of stations were differentiated: the stations characterized by the mangrove and those under the influence of seagrass beds. A seasonal cycle, opposing the dry periods to the others, was observed.Thus, it seems that the use of the mangrove habitat by the fishes is optimized through a complete reorganization of communities in terms of species composition whereas the overall number and biomass remain stable. This model remains valid even for the most constraining biota of the mangrove ecosystem inhabited by a small number of well adapted species.     

Movement patterns of catfishes (Ariidae) in a tropical semi‐arid estuary

From December 2005 to November 2006, 216 samples were taken from the main channel of the Goiana Estuary, representing a total sampled area of 23 ha. Ariidae species were the most abundant in density (1600 individuals ha^?1, 53%) and biomass (18 813 g ha^?1, 63%). Cathorops spixii was the most abundant in density (1340 individuals ha^?1) and biomass (14 203 g ha^?1). The variables: number of species, total density and biomass, showed significant interactions between the factors of areas and seasons (P < 0·01). The highest total density (7394 individuals ha^?1) and biomass (70 292 g ha^?1) occurred in the middle and upper estuaries, respectively, during the early‐rainy season. The density of C. spixii differed significantly between areas and seasons (P < 0·01), while Cathorops agassizii differed significantly only between seasons (P < 0·01). The biomass differed significantly for the species C. spixii, C. agassizii and Sciades herzbergii between seasons, and C. spixii and C. agassizii between areas. Also, the density and biomass of C. spixii and C. agassizii showed interaction between areas and seasons. Only the biomass of S. herzbergii showed interaction between areas and seasons (P < 0·01). This indicates that seasonal variations influenced the distribution of Ariidae species in the different areas of the Goiana Estuary. Moreover, canonical correspondence analysis highlighted a strongly significant correlation (P < 0·01) between the seasonal variations of the environmental gradients (salinity and water temperature) and distribution of catfishes. The management and conservation of estuaries should take into account the life cycle of these species in different estuarine areas and hydrological seasons.