Effective monitoring of freshwater fish

This is the pre-peer reviewed version (preprint) of the article: "Effective monitoring of freshwater fish". 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. Freshwaters are, however, particularly vulnerable to anthropogenic impacts, including habitat loss, climate and land use change, nutrient enrichment, 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 assemblages. 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 its 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 emphasise 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 will help programmes improve understanding processes that shape the Earth's freshwater ecosystems, and help protect these systems in face of rapid environmental change.This paper is based on a workshop funded by the Spanish Ministry of Science, Innovation and Universities (project CGL2015-69311-REDT). Additional financial support was provided by the same ministry (projects ODYSSEUS, BiodivERsA3-2015-26, PCIN-2016-168 and CGL2016-80820-R) and the Government of Catalonia (ref. 2014 SGR 484 and 2017 SGR 548)