Abstract
River fragmentation and alterations in flow and thermal regimes are the main stressors affecting migrating fish, which could be aggravated by climate change and increasing water demand. To assess these impacts and define mitigation measures, it is vital to understand fish movement patterns and the environmental variables affecting them. This study presents a long-term (1995–2019) analysis of upstream migration patterns of anadromous and potamodromous brown trout in the lower River Bidasoa (Spain). For this, captures in a monitoring station were analyzed using Survival Analysis and Random Forest techniques. Results showed that most upstream movements of potamodromous trout occurred in October–December, whereas in June–July for anadromous trout, although with differences regarding sex and size. Both, fish numbers and dates varied over time and were related to the environmental conditions, with different influence on each ecotype. The information provided from comparative studies can be used as a basis to develop adaptive management strategies to ensure freshwater species conservation. Moreover, studies in the southern distribution range can be crucial under climate warming scenarios, where species are expected to shift coldwards.
Highlights
Current society needs a large volume of fresh water to keep its present lifestyle, whether for irrigation, power generation, flood control, or industrial and domestic supply
Riverine trout was more abundant than sea trout (88.3% vs 11.7%; EP test P-value: P \ 0.0001) but with smaller size (Table 1, Mann–Whitney Wilcoxon (MW) test for FL and W P \ 0.0001)
Proportion of females was greater than males for both ecotypes
Summary
Current society needs a large volume of fresh water to keep its present lifestyle, whether for irrigation, power generation, flood control, or industrial and domestic supply. Freshwater fish use flow and thermal regimes as main ecological timers for initiating and maintaining behavioral reactions such as migration, feeding, and spawning (Lucas et al, 2001) Alterations on these regimes can lead to a loss of the migration signal and a consequent migration delay (Garcıa-Vega et al, 2018), difficult obstacle ascent and reduction of habitat connectivity (Ovidio & Philippart, 2002; Garcıa-Vega et al, 2021), a shift in the phenology, and a mismatch between available and necessary resources (Shuter et al, 2012; Otero et al, 2014). This can derive in population and diversity reductions caused by the mismatch among offspring and ecological requirements (Nicola & Almodovar, 2002) and changes in fish assemblages (Shea & Peterson, 2007), as well as a reduction of suitable physical and thermal habitat availability (Almodovar et al, 2012; Boavida et al, 2015; Junker et al, 2015), endangering the persistence of many migratory fish species (Shuter et al, 2012) such as the brown trout (Salmo trutta Linnaeus, 1758)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
