The interaction rainfall vs. weight as determinant of total mercury concentration in fish from a tropical estuary.

Mercury loads in tropical estuaries are largely controlled by the rainfall regime that may cause biodilution due to increased amounts of organic matter (both live and non-living) in the system. Top predators, as Trichiurus lepturus, reflect the changing mercury bioavailability situations in their muscle tissues. In this work two variables [fish weight (g) and monthly total rainfall (mm)] are presented as being important predictors of total mercury concentration (T-Hg) in fish muscle. These important explanatory variables were identified by a Weibull Regression model, which best fit the dataset. A predictive model using readily available variables as rainfall is important, and can be applied for human and ecological health assessments and decisions. The main contribution will be to further protect vulnerable groups as pregnant women and children. Nature conservation directives could also improve by considering monitoring sample designs that include this hypothesis, helping to establish complete and detailed mercury contamination scenarios.

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.