Tracking the migration and distribution of Caspian Kutum (Rutilus kutum, Kamenskii, 1901) along the southern coastline of the Caspian Sea based on stable isotope analysis

Animal movements and resource utilization are essential factors for effective environmental management, but they are difficult to quantify in extensive natural ecosystems such as the aquatic environment. Stable isotope analysis is an ecological tracer technique that reveals information about links between trophic levels, movement patterns of migratory species or geographical variations due to the different aquatic processes that influence them. The Caspian kutum is an important commercial endemic species on the southern coasts of the Caspian Sea and can be used as a proxy to gain information on how different spatiotemporal, environmental and biological—variables can influence ecological tracers such as stable isotopes at the sea basin level. Thus, the main objective of this study is to investigate how spatiotemporal, isotopic baseline and environmental factors influence the distribution of stable isotopes in the Caspian kutum. The results showed that although there are individual variations, there is an overall increasing trend in δ13C and a decreasing trend in δ15N from the western to the eastern regions. In addition, there is a decreasing trend in δ13C and an increasing trend in δ15N with increasing age. It seems that among other migration routes of this species from the northern part of the southern Caspian Sea to the southern coasts, one of the main migration routes of this fish on the coasts of Iran is west‐east mobility, which may affect the efficiency of sustainable management of the catch in various fishing areas. This was the first study to establish a migratory pattern of the Caspian kutum based on stable isotopes. We advocate the wider stable isotopes to effectively investigate fish migratory, as the results from this study provided important contributions to the development of valuable insights for the management and sustainability for this threatened and declining species fish populations.