Identifying the factors affecting the reduction of Caspian lamprey population (Caspiomyzon wagneri Kessler, 1870) in Shiroud River: The need to adopt management-protection policies

The Caspian lamprey (Caspiomyzon wagneri) is one of the most important ecological and native fish species of the Caspian Sea basin. The present study was conducted to identify the factors affecting the population decline of this species in Shiroud River as one of the important habitats of fish in the southern basin of the Caspian Sea. For this purpose, three stations were selected for sampling fish in downstream of Shiroud River. In this study, immediately after fish fish sampling, physicochemical parameters of water including pH, Total Dissolved Solids (TDS), Electrical Conductivity (EC), water temperature, salinity and Dissolved Oxygen (DO) were recorded. In this study, the correlation between physicochemical parameters of water was investigated using Pearson correlation. Also, Canonical Correspondence Analysis was used to investigate the relationship between environmental parameters and the abundance of C. wagneri. Along with the study of physicochemical factors affecting the Caspian lamprey population, the origin of human activities in the study area, which affects these factors and ultimately the population structure of the species, was investigated by collecting field information. Based on the results, there was a significant correlation between temperature and salinity. The results showed that EC and pH factors had the greatest effect on the abundance of fish in Shiroud River. Given the importance of the reproductive cycle of cormorants in the Caspian Sea basin, the present study suggests that preventing habitat destruction, especially spawning sites, should be a priority. Therefore, avoiding the entry of pollutants into the river and dredging and sand extraction should be considered.