A comparison of flooded forest and floating meadow fish assemblages in an upper Amazon floodplain

Sandra Bibiana Correa, Will G.R. Crampton, Lauren J. Chapman and James S. Albert

This study was conducted as part of my master thesis (University of Florida).  The research was conducted in Pacaya-Samiria National Reserve, Peruvian Amazon. The aim of the project was to do a quantitative comparison of fish assemblage structure from flooded forests and floating meadows of macrophytes and to evaluate the degree to which these contiguous, connected habitats are characterized by distinct fish faunas during the flooding season. Using matched sets of gill nets of different mesh sizes, fish species richness and composition, abundance, diel variation, and body-size distributions were compared between 10 flooded forest and 10 floating meadow sites. An overriding pattern of similarity emerged between these two habitats. Averaged across sampling sites, the mean abundance of fish, mean biomass, mean and maximum standard length, and mean mass did not differ significantly between flooded forest and floating meadows.  However, the area of the flooded forest was estimated to be approximately 200 times greater than that of floating meadows; thus, when scaled to total area, flooded forests have a much larger total fish biomass. Species abundances followed a strong negative exponential distribution in which three species accounted for 60-70% of the total abundance in either habitat. Despite these similarities multivariate analyses demonstrated subtle differences between the assemblages in flooded forest and adjacent floating meadows. In addition, species richness was higher in flooded forest, reflecting a high percentage of unique species. Higher abundance and species richness were observed in nocturnal samples of both habitats; however, among diurnal samples, more species were active in floating meadows.

Seasonal variation in abundance and distribution of fishes in a floodplain-lake in the Colombian Amazon

Sandra Bibiana Correa

I conducted this study as part on my undergraduate thesis (Universidad del Valle, Cali, Colombia). In this study I investigated changes in fish abundance and spatial distribution of medium- and large-sized fishes (>100 mm) in an oxbow lake of the lower Apaporis River, Colombian Amazon, across three seasons (falling, low, and rising water).   Fifty-three species in 13 families were collected from six habitats: lagoon channels, stream, flooded forests, isolated shrub patches, muddy beaches, and rocks. Abundance, biomass, and species richness were higher during the rising-water season and lower during falling-water season.  Correspondence analysis (CA) showed that fish assemblages were associated to two basic habitat types.  One assemblage of fishes was associated with densely vegetated and structurally complex habitats (flooded forest, lagoon channels, stream, and isolated shrub patches), and a second assemblage of fishes was associated with muddy beaches.  These assemblages persisted despite seasonal fluctuations in water level.  Species in the structurally complex habitats assemblage were mostly omnivores, whereas the beach habitat assemblage included mainly piscivores and detritivores.  Results from this study suggest that overall abundance of fishes in habitats within and surrounding Taraira Lake is highly variable among seasons, but species habitat affinity is maintained through seasons.

Updated August 19, 2008