Investigation on the relationship between environmental factors and distribution of Kermanshah stone loach (Sasanidus kermanshahensis) in Dinor river using Generalized Additive Model (GAM)

The aim of this study was to investigate the relationship between environmental parameters and the distribution of Kermanshah stone loach (Sasanidus kermanshahensis) in Dinor River from Tigris drainage in Kermanshah Province. sampling was performed in April 2017 at 7 stations along the river. Characteristics of each station including altitude, water flow velocity, river width, water depth, characteristics of bed components including bedrock percentage and average diameter bedrock was measured immediately after fish sampling. The Generalized Additive Model (GAM) was used to investigate the effect of environmental parameters on the distribution of S. kermanshahensis. Among the studied variables, the altitude, flow velocity, river width and bed index were significant,. Based on four significant factors, the distribution model algorithm and the presence of Kermanshah stone loach were obtained.With the increase of bed index from 4 to 6, and with the increase of altitude from 840 to 1050 m above sea level (MASL), the abundance of S. kermanshahensis decreased. In addition, with increasing the width of the river from 2 to 15 m, the abundance of fish increased. The results showed that with increasing the water flow velocity from 0.4 to 0.9 m/s, the frequency of S. kermanshahensis increased, but after that, with increasing the flow velocity up to 2 m/s, the fish abundance decreased sharply. Overall, downstream areas of the river, especially stations 6 and 7 (towards Bisotun in Harsin County), which have a river bed with fine particles and low flow velocity, can be a suitable habitat for Kermanshah stone loach.