Freshwater ecosystems constitute only a small fraction of the planet's water resources, yet support much of its diversity, with freshwater fish accounting for more species than birds, mammals, amphibians or reptiles. Fresh waters are, however, particularly vulnerable to anthropogenic impacts, including habitat loss, climate and land use change, pollution and biological invasions. This environmental degradation, combined with unprecedented rates of biodiversity change, highlights the importance of robust and replicable programmes to monitor freshwater fish. Such monitoring programmes can have diverse aims, including confirming the presence of a single species (e.g., early detection of alien species), tracking changes in the abundance of threatened species, or documenting long‐term temporal changes in entire communities. Irrespective of their motivation, monitoring programmes are only fit for purpose if they have clearly articulated aims and collect data that can meet those aims. This review, therefore, highlights the importance of identifying the key aims in monitoring programmes and outlines the different methods of sampling freshwater fish that can be used to meet these aims. We emphasize that investigators must address issues around sampling design, statistical power, species’ detectability, taxonomy and ethics in their monitoring programmes. Additionally, programmes must ensure that high‐quality monitoring data are properly curated and deposited in repositories that will endure. Through fostering improved practice in freshwater fish monitoring, this review aims to help programmes improve understanding of the processes that shape the Earth's freshwater ecosystems and help protect these systems in face of rapid environmental change.

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Aim:To analyse the occurrence and abundance of native versus alien fish species in relation to climate, land use, hydrologic alteration and habitat fragmentation in a heavily invaded and human-impacted riverine ecosystem. To test whether co-occurrence patterns of native versus alien species are structured by environmental filtering or biotic associations.Location: Mediterranean, Iberian Peninsula, Ebro River catchment. Methods:We modelled freshwater fish distributions and their association with environmental conditions using a hurdle model-like approach involving boosted regression trees. Additionally, we applied a joint species distribution model to quantify the co-occurrence of native versus alien fish species that can be attributed to shared environmental responses or potentially to biotic interactions. Results:Our results point to environmental factors, rather than biotic associations, as major correlates of the increase of alien and the decline of native fishes in the Ebro River. We observed contrasting patterns of native versus alien species along the upstream-downstream gradient. Alien species dominated in the lower reaches associated with warmer temperatures, higher shares of intensive land use and appeared facilitated by dams and river regulation. Native species richness was highest in the larger tributaries followed by a strong decline in the main stem which was related to the river network position and land use type. Fragmentation played a subordinate role in explaining fish richness and abundance patterns.Main conclusions: Given the strong association with temperature, a further range expansion of alien fishes in the Ebro with future climate change may be expected.More local-scale factors related to habitat degradation and hydrologic alteration will further exacerbate the invasion success of many alien fishes. Further multiple, independent species introductions might mask isolation and fragmentation effects of dams on the future spread and distribution of alien fish. K E Y W O R D Sboosted regression trees, Ebro River, environmental filtering, freshwater fish, habitat degradation, invasive alien species, joint species distribution model, native species decline, species co-occurrence

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Soares Costa, RM.; Martinez-Capel, F.; Muñoz Mas, R.; Alcaraz-Hernández, JD.; Garófano-Gómez, V. (2012). Habitat suitability modelling at mesohabitat scale and effects of dam operation on the endangered Júcar nase, Parachondrostoma arrigonis (River Cabriel, Spain). River Research and Applications. 28(6):740-752. doi:10.1002/rra.1598. 1 This is a pre-copyedited, author-produced PDF version following peer review of this article, which has been 1 published in definitive publisher-authenticated form at: Habitat suitability models and effects of dam operation on the endangered Júcar nase, 6Parachondrostoma arrigonis (river Cabriel, Spain)