Influence of environmental and human factors on fish distribution pattern of Karaj River

Although substantial studies are available as regards the abundance, richness and composition of freshwater fish along altitudinal slops, the impact of human factors such as dam construction are rarely considered. In this study, the effects of the environmental and human factors on longitudinal patterns of fish faunal changes, species richness and fish abundance from upstream to downstream in the southern profile of the central Alborz Protected Area were examined using Redundancy Analysis (RDA) and Generalized Linear Models (GLM). The Karaj River was divided into three zones based on habitat structure, physicochemical variables and species composition. The results indicate that chemical variables can be more effective in some conditions including small changes in habitat structure and physical variables along the altitudinal slope and can be a justification for the abundance, richness and composition of species. Typically, in highly polluted rivers, chemical agents can be a good explanation for the presence or absence of species. Human disturbances, such as dams, change the expected distribution patterns of fish along the altitudinal slope by decreasing outlet water temperature and also creating homogeneous and simple habitats. Therefore, the implementation of conservation programs should be a priority for the Karaj River fishes, especially in the middle areas which are affected by these threats.