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We reviewed information on Iberian freshwater fish to characterize their migratory status and identify migration reasons and periods. Most species migrate (87.3 %; 62 species from 15 families). A large number are potamodromous species (45 species from 6 families) but diadromous species (17 species from 11 families) also exist, including anadromous (9 species) and cata¬dromous (8 species). The spawning period is a primary driver of fish migration but feeding and refuge-associated migrations also take place. Sexual maturity is the most important cue triggering fish migration, and other important factors include water temperature, river flow, currents, salinity and photoperiod. Spawning and migrating periods are in general prolonged and vary among years, as a response to the environmental variability of Mediterranean river systems, which are the most frequent in the Iberian Peninsula. Migratory movements of the various native species of each site cover almost the whole or the whole year. Therefore, to allow fish migration, Iberian freshwaters should always be connected, or their fish passes should be permanently, or practically always, in operation.

Body size is an important functional trait that can be used as a bioindicator to assess the impacts of perturbations in natural communities. Community size structure responds to biotic and abiotic gradients, including anthropogenic perturbations across taxa and ecosystems. However, the manual measurement of small-bodied organisms such as benthic macroinvertebrates (e.g., >500 µm to a few centimeters long) is time-consuming. To expedite the estimation of community size structure, here, we developed a protocol to semi-automatically measure the individual body size of preserved river macroinvertebrates, which are one of the most commonly used bioindicators for assessing the ecological status of freshwater ecosystems. This protocol is adapted from an existing methodology developed to scan marine mesozooplankton with a scanning system designed for water samples. The protocol consists of three main steps: (1) scanning subsamples (fine and coarse sample size fractions) of river macroinvertebrates and processing the digitized images to individualize each detected object in each image; (2) creating, evaluating, and validating a learning set through artificial intelligence to semi-automatically separate the individual images of macroinvertebrates from detritus and artifacts in the scanned samples; and (3) depicting the size structure of the macroinvertebrate communities. In addition to the protocol, this work includes the calibration results and enumerates several challenges and recommendations to adapt the procedure to macroinvertebrate samples and to consider for further improvements. Overall, the results support the use of the presented scanning system for the automatic body size measurement of river macroinvertebrates and suggest that the depiction of their size spectrum is a valuable tool for the rapid bioassessment of freshwater ecosystems, This work was supported by the Spanish Ministry of Science, Innovation and Universities (grant number RTI2018-095363-B-I00), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

The global increase of cyanobacterial blooms occurrence has been associated with the presence of compounds that generate earthy and musty odour in freshwater systems, among which geosmin stands out. The lack of information on the factors associated to geosmin production by benthic organisms has driven the development of this study, whose main goal is to determine the effects of nutrient concentration and DIN:SRP ratio on geosmin formation and release. The experiment was performed in 18 microcosms under controlled conditions for 21 days, using a natural biofilm suspension from Ter river (NE, Spain) to promote biofilm settlement. Six treatments were set crossing three DIN:SRP ratios (A = 4:1, B = 16:1 and C = 64:1) with two nutrient concentrations (Low and High). After 7 days of experiment, geosmin was detected in biofilm, being higher under high nutrient concentration and low DIN:SRP ratio conditions. In this treatment, geosmin in biofilm reached its maximum concentration at day 16 (3.8 ± 0.9 ng/mg), decreasing at the end of the experiment (21d) due to cyanobacteria detachment and geosmin release into the water (136 ± 6 ng/L). Overall, this experimental study showed that high nutrient concentration and low DIN:SRP ratio favoured the Oscillatoria genus development within biofilm communities, generating the optimal conditions for geosmin production. The interaction between these two factors was demonstrated to be a potential driver of benthic geosmin production and release, and should be monitored and controlled in rivers exploited for drinking water purposes. We would like to acknowledge the water utilities Aigües de Vic S.A. and Aigües d'Osona S.A. (Catalonia, Spain), for their funding support in the study presented in this publication. We also want to thank the help provided by Dr. Helena Guasch and Ms. Núria Pou in identifying the algal community present in the biofilm samples, and the help provided by Dr. Victoria Osorio and Dr. Joan Colon in the development of the analytical method for geosmin. The research leading to these results has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program – H2020 INTCATCH (grant agreement n° 689341 ). LP has received funding from the Postdoctoral Fellowships Programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 Programme of Research and Innovation of the European Union under the Marie Skłodowska-Curie Grant Agreement No. 801370

In May and October 2013, an in situ assessment of the fish ramp at the gauging station on the Fluvià River at Olot was performed, using different techniques to estimate the fish ramp’s effectiveness. This fish ramp is one of the first in Catalonia (NE Iberian Peninsula) that follows international guidelines for fish passes and especially for fish ramps. The fish ramp allowed passage of all native cyprinid species from this river. The crossing rates were higher in May (average of 7.9 ind./day for Barbus meridionalis and 3.8 ind./day for Squalius laietanus), a month associated with their spawning period, than in October (average of 4.6 ind./day for B. meridionalis and 1.0 ind./day for S. laietanus). Pending complementary year-round samplings for several annual periods, the results show that the spawning period seems to be the primary driver of upstream fish migration, which is also influenced by a decrease in river flow just after a peak flow, a minimum water temperature value and less bright lunar phases., Durante los meses de mayo y octubre de 2013, se realizó una evaluación in situ de la rampa para peces de la estación de aforo del río Fluvià en Olot utilizando diferentes técnicas para estimar su eficacia. Esta rampa para peces es una de las primeras de Cataluña (NE Península Ibérica) que sigue directrices internacionales para dispositivos de paso para peces y, especialmente, para rampas para peces. Esta rampa permitió el paso de todas las especies de ciprínidos autóctonos de este río. Las tasas de franqueo fueron más altas en mayo (media de 7.9 ind./día para Barbus meridionalis y 3.8 ind./día para Squalius laietanus), asociadas con su período de freza, que en octubre (media de 4.6 ind./día para B. meridionalis y 1.0 ind./día para S. laietanus). Pendiente de muestreos complementarios realizables durante varios períodos anuales, el periodo de freza parece ser el principal impulsor de la migración río arriba, que también se ve influida por una disminución de caudal justo después de puntas de caudal, un mínimo de temperatura del agua y las fases lunares menos luminosas.

In spite of being a widespread activity causing the salinization of rivers worldwide, the impact of potash mining on river ecosystems is poorly understood. Here we used a mesocosm approach to test the effects of a salt effluent coming from a potash mine on algal and aquatic invertebrate communities at different concentrations and release modes (i.e. press versus pulse releases). Algal biomass was higher in salt treatments than in control (i.e. river water), with an increase in salt-tolerant diatom species. Salt addition had an effect on invertebrate community composition that was mainly related with changes in the abundance of certain taxa. Short (i.e. 48 h long) salt pulses had no significant effect on the algal and invertebrate communities. The biotic indices showed a weak response to treatment, with only the treatment with the highest salt concentration causing a consistent (i.e. according to all indices) reduction in the ecological quality of the streams and only by the end of the study. Overall, the treatment's effects were time-dependent, being more clear by the end of the study. Our results suggest that potash mining has the potential to significantly alter biological communities of surrounding rivers and streams, and that specific biotic indices to detect salt pollution should be developed.

Nota sobre les consequencies de la invasio del mol·lusc d'aigua dolca, Anodonta woodiana, a la Peninsula Iberica

The Water Framework Directive includes fish fauna as one of the biological elements, jointly with aquatic flora and benthic invertebrates, to assess and monitor water and habitat quality. Successful implementation of the Directive depends in part on the development of reliable, science-based tools to directly assess biological conditions. Although fish have been used as ecological indicators for more than 30 years around the world, mainly in North America and more recently in Europe, few studies have been done in Mediterranean streams. Fish assemblages of the Mediterranean basin, similarly to other Mediterranean areas such as California, have particular characteristics that hamper IBI’s development: few native species, poor knowledge of their ecological requirements, high number of endemisms with a wide range of tolerance to environmental variations and many exotic species. This chapter summarizes our experience in developing fish-based tools in Catalonia. We discuss the challenges and difficulties to develop these approaches in Mediterranean streams. We show the IBICAT2010 as a fish-based assessment method suitable for the evaluation of the ecological status of Catalan rivers. Moreover, we assess size-related variables as a bioassessment tool because population size structure can provide insights into species-specific applications and management. Finally, we analyse the longitudinal connectivity throughout Catalan rivers and fish passes by using the index of river connectivity (ICF) specially designed to Catalan rivers.