Many fish species need to move between different habitats in order to complete their life cycles. As a result, migration responds to internal and external factors, with environmental variables, such as river flow and thermal regimes, acting as the main stimuli for the onset and maintenance of migratory behavior in freshwater fish. Moreover, river fragmentation and anthropogenic alterations on these variables (e.g. river regulation) may have strong impacts on fish populations, which could be aggravated by future projections of climate change and increasing water demand. Thus, to assess these impacts and define mitigation measures, it is vital to understand fish movement patterns and the environmental variables affecting them.
Native Iberian fish fauna presents the greatest European percentage of endemism, characterized by a low number of families, with most species belonging to the Cyprinidae family. The most representative species from this family are barbels and nases, for example, the Iberian barbel and the Northern straight-mouth nase. However, scarce information exists regarding the ecological requirements of these endemic species during their upstream migration. Another important family in the Iberian Peninsula, in terms of recreational fishing and ecological traits, is the Salmonidae, the brown trout being one of the most representative salmonids worldwide. Although this species has been deeply studied, most available research has been focused on anadromous populations, and studies in the south of its natural distribution are still scarce.
The long-term monitoring is an essential tool, not only for identify population changes, migration patterns and cues, but also for the evaluation of the overall effect of changes in the parameters involved in the migration and assessing the effects of mitigation measures. Therefore, continuous monitoring studies are necessary to define adaptive strategies and reliable management plans to ensure the conservation of Iberian freshwater fish.
