Geographic barriers: Do the intervene in the composition and longitudinal distribution of the fish community in a river?

Abstract

Several variables are involved in the patterns of distribution and spatio-temporal occupation of fish in a fluvial system. In this study, we evaluate numerous geographic (cascades, waterfalls and riffles) and physicochemical variables (slope, current velocity, pH, conductivity and dissolved oxygen) in different sections of the Quimán River, and its relationship with fish assemblage. This river is a mountain stream and presents an abrupt orography with various waterfalls, cascades and riffles that affect the connectivity of the river. Therefore, the working hypothesis was to establish if some of these geography and physicochemical variables can influence the spatial segregation of fish in the river. The results showed a significant variation (ANOSIM r = 0.6 p = 0.0006) in the composition of the assemblage along the river, defining a spatial segregation for native species, and a preferential habitat use was established by native species due to low current velocity environments (< 0.64 m s^-1) and slope less than 3.5%. Nevertheless, a BEST/BIOENV analysis determined a low relationship between environmental variables and fish assemblage distribution (r = 0.37 p = 0.03). On the other hand, frequency of waterfalls, cascades and riffles decreased in the direction of the flow, in contrast to richness and diversity, even when there is a pisciculture and treatment plant of wastewater in the terminal section. It is suggested to develop more specific studies to understand the influence of geographic variables on native fish populations.