Composition and structure of the fish fauna in the lower section of the Gaira River, Sierra Nevada of Santa Marta (SNSM), in the Colombian Caribbean

Typical rivers of large continental masses flow into the Pacific and Caribbean coasts of Colombia, and in turn, small streams of coastal mountains. In large rivers the diversity of species is high compared to coastal streams. In contrast, the mountain basins present a greater abundance of amphidromous species than primary ones. In this research, the composition of the fish fauna of the lower sector of the Gaira River on the northwestern slope of the Sierra Nevada de Santa Marta (SNSM) was analyzed. The samplings were carried out in the rainy and dry seasons with the objective of knowing the composition and determining possible correlations in the structure, and between the fish with the substrate, for which, principal component analysis (PCA) and Analysis of of Canonical Correspondence (ACC) among others. 967 individuals were collected, distributed in 11 orders, 13 families and 23 species, of which six (26.8%) are considered purely freshwater, 15 (65.21%) are estuarine species, and two (8.69 %) are marine. The ACP differentiated two biotopes, backwaters and rapids, and the ACC showed that pH is the most important environmental variable in the distribution of species. The change in seasonality originated variation in the flow rate that affected the abundance and affected the structure of the habitat. This alteration generated hydrological variations that were reflected in the fish communities in the dry season due to the interruption of the flow of water between the upper, middle and lower parts of the river.