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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.

Trends and ecological consequences of phosphorus (P) decline and increasing nitrogen (N) to phosphorus (N:P) ratios in rivers and estuaries are reviewed and discussed. Results suggest that re-oligotrophication is a dominant trend in rivers and estuaries of high-income countries in the last two-three decades, while in low-income countries widespread eutrophication occurs. The decline in P is well documented in hundreds of rivers of United States and the European Union, but the biotic response of rivers and estuaries besides hytoplankton decline such as trends in phytoplankton composition, changes in primary production, ecosystem shifts, cascading effects, changes in ecosystem metabolism, etc., have not been sufficiently monitored and investigated, neither the effects of N:P imbalance. N:P imbalance has significant ecological effects that need to be further investigated. There is a growing number of cases in which phytoplankton biomass have been shown to decrease due to re-oligotrophication, but the potential regime shift from phytoplankton to macrophyte dominance described in shallow lakes has been documented only in a few rivers and estuaries yet. The main reasons why regime shifts are rarely described in rivers and estuaries are, from one hand the scarcity of data on macrophyte cover trends, and from the otherhand physical factors such as peak flows or high turbidity that could prevent a general spread of submerged macrophytes as observed in shallow lakes. Moreover, re-oligotrophication effects on rivers may be different compared to lakes (e.g., lower dominance of macrophytes) or estuaries (e.g., limitation of primary production by N instead of P) or may be dependent on river/estuary type. We conclude that river and estuary re-oligotrophication effects are complex, diverse and still little known, and in some cases are equivalent to those described in shallow lakes, but the regime shift is more likely to occur in mid to high-order rivers and shallow estuaries. This work was supported by a grant from the U.S. National Science Foundation (#DBI-1639145) to the National Socio-Environmental Synthesis Center (Rivershift Project). The work was also financially supported by the Catalan Government through the funding grant ACCIÓ-Eurecat (Project AquaSCI-2022).

Gillnet selectivity is poorly understood for most freshwater fish species, particularly for invasive alien species. However, their use to determine mesh selectivity could be essential for establishing management measures, such as the selective removal of exotic invasive species. This study aims to the assess size selectivity of exotic invasive species in a restored lentic freshwater ecosystem. Therefore, we analysed gillnet size selectivity based on experimental fishing trials performed by using multimesh gillnets. Twice a year, for 8 years, multimesh nylon gillnets were set up in the Estany d’Ivars i Vila-sana, a restored shallow lake in Catalonia (NE Iberian Peninsula). We caught 4105 individuals belonging to three widely distributed freshwater fish species—3583 pikeperches (Sander lucioperca (Linnaeus, 1758)), 115 common roaches (Rutilus rutilus (Linnaeus, 1758)) and 407 common carps (Cyprinus carpio, Linnaeus, 1758). The SELECT method was applied to fit six different gillnet selectivity uni- and bimodal models. As a result, bi-lognormal provides the best fit for the three species. This is in line with previous studies that found size–frequency data skewed to the right or to multimodal models when high numbers of fish are captured. These results provide the essential information required for fish community management with the presence of these invasive alien species.

As the number of introduced species keeps increasing unabatedly, identifying and prioritising current and potential Invasive Alien Species (IAS) has become essential to manage them. Horizon Scanning (HS), defined as an exploration of potential threats, is considered a fundamental component of IAS management. By combining scientific knowledge on taxa with expert opinion, we identified the most relevant aquatic IAS in the Iberian Peninsula, i.e., those with the greatest geographic extent (or probability of introduction), severe ecological, economic and human health impacts, greatest difficulty and acceptability of management. We highlighted the 126 most relevant IAS already present in Iberian inland waters (i.e., Concern list) and 89 with a high probability of being introduced in the near future (i.e., Alert list), of which 24 and 10 IAS, respectively, were considered as a management priority after receiving the highest scores in the expert assessment (i.e., top-ranked IAS). In both lists, aquatic IAS belonging to the four thematic groups (plants, freshwater invertebrates, estuarine invertebrates, and vertebrates) were identified as having been introduced through various pathways from different regions of the world and classified according to their main functional feeding groups. Also, the latest update of the list of IAS of Union concern pursuant to Regulation (EU) No 1143/2014 includes only 12 top-ranked IAS identified for the Iberian Peninsula, while the national lists incorporate the vast majority of them. This fact underlines the great importance of taxa prioritisation exercises at biogeographical scales as a step prior to risk analyses and their inclusion in national lists. This HS provides a robust assessment and a cost-effective strategy for decision-makers and stakeholders to prioritise the use of limited resources for IAS prevention and management. Although applied at a transnational level in a European biodiversity hotspot, this approach is designed for potential application at any geographical or administrative scale, including the continental one., This research was supported by the LIFE INVASAQUA project (Aquatic In- vasive Alien Species of Freshwater and Estuarine Systems: Awareness and Prevention in the Iberian Peninsula) (LIFE17 GIE/ES/000515) funded by the EU LIFE Program. The Fundación Biodiversidad (Government of Spain) and the Government of Navarre financially support specific actions into the LIFE INVASAQUA. F.R. is supported by Foundation for Science and Technology through an individual contract (CEEC/0482/2020). J.E. has a Ph.D. scholarship (SFRH/BD/140556/2018) funded by FCT, Portugal. F.B. is supported by Foundation for Science and Technology through an individual contract (CEEC/01896/2021).

Este artículo contiene 17 páginas, 6 figuras, 3 tablas., The stress-gradient hypothesis predicts that biotic interactions within food webs are context dependent, since environmental stressors can attenuate consumer–prey interactions. Yet, how heavy metal pollution infuences the impacts of predatory fsh on ecosystem structure is unknown. This study was conducted in the Osor stream (Spain), which features a metal (mainly Zn) pollution gradient. We aimed to determine how the responses of benthic communities to the presence and absence of predatory fsh interact with environmental stress and to test whether the top-down control of top predators is context dependent. To address these questions, periphyton biomass and macroinvertebrate densities were determined throughout an exclosure/ enclosure mesocosm experiment using the Mediterranean barbel (Barbus meridionalis) as a top predator. The monitoring study showed that metal accumulation in periphyton and macroinvertebrates refected patterns observed in water. The mesocosm study showed that fsh predation efects on larval chironomids were not context-dependent and that periphyton biomass was markedly lower in the presence of fsh regardless of metal pollution levels. This strong top-down control on periphytic algae was attributed to the foraging behaviour of fsh causing bioturbation. In contrast, the top predator removal revealed grazer-periphyton interactions, which were mediated by heavy metal pollution. That is, periphyton beneftted from a lower grazing pressure in the metal-polluted sites. Together, our results suggest that the top–down control by fshes depends more on functional traits (e.g. feeding behaviour) than on feeding guild, and demonstrate the capacity of top predators to modify anthropogenic stressor efects on stream food-web structure., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research was supported by the Spanish Ministry of Science, Innovation and Universities (projects CGL2013‐43822‐R and CGL2016‐80820‐R, AEI/FEDER/EU) and the Government of Catalonia (ref. 2017 SGR 548 and CERCA Programme). F. Rubio‐Gracia and M. Argudo beneftted from a predoctoral fellowship from the University of Girona (IFUdG2017) and the Agency for Management of University and Research Grants (AGAUR) of the Government of Catalonia (2016 FI-B 00284), respectively.

We provide a unique fish individual body size dataset collected from our own sampling and public sources in north-eastern Spain. The dataset includes individual body size measures (fork length and mass) of 12,288 individuals of 24 fish species within 10 families collected at 118 locations in large rivers and small streams. Fish were caught by one-pass electrofishing following European standard protocols. The fish dataset has information on the local instream conditions including climatic variables (i.e., temperature and precipitation), topography (i.e., altitude), nutrient concentration (i.e., total phosphorus and nitrates), and the IMPRESS values (a measure of cumulative human impacts in lotic ecosystems). The potential uses of this new fish dataset are manifold, including developing size-based indices to further estimate the ecological status of freshwater ecosystems, allometric models, and analysis of variation in body size structure along environmental gradients We thank all people who participated in the fish sampling and the agencies Agència Catalana de l'Aigua (ACA) and Confederación Hidrográfica del Ebro (CHE) for their help. The original sampling and this study were financially supported by ACA, CHE, and the Spanish Ministry of Science and Innovation [grants ref. RTI2018-095363-B-I00, PID2019-103936GB-C21]

Rivers are among the most biodiverse and endangered ecosystems on earth. In Europe, concern over their conservation promoted the development of legal instruments for habitat and species conservation, the Habitats Directive, and water resource management, the Water Framework Directive. This legal protection demanded the estimate of river ecosystem surface for different purposes. Different approaches allow river surface to be measured at a low cost. Some accurate techniques like satellite images or LiDAR (Light Detection and Ranging) do not always work at a large scale or for streams and small rivers. We discuss here the use of the traditional hydraulics relationship between drainage area and bankfull width as a good approach to river surface estimation. We confirm that the use of this cheap and simple method could be a good approach to estimate river surface. However, we also proved that the development of regional curves, i.e., to establish the empirical relationship based on study area data, constitutes an essential improvement to estimation. This research was funded by the Ministry of Ecological Transition and Demographic Challenge, project number 3081147. This research was supported by the Government of Catalonia (CERCA Program).

Length&ndash, weight relationships (LWRs), condition factors, and their variation over time were analyzed for four exotic freshwater fish (bleak, common carp, pikeperch, and roach) in the Estany d&rsquo, Ivars i Vila-sana shallow lake in Catalonia, Northern Spain. Fish samples were collected twice a year (early summer and autumn), between 2008 and 2016, by using between three and five multi-mesh nylon gillnets. This study provides novel information about four common exotic fishes outside of their natural range and within the context of a restored shallow lake, where the ichthyologic community is evolving in concordance with the ecosystem conditions and the fish community dynamics.

Este artículo contiene 9 páginas, 6 figuras, 3 tablas., Flow regimes are important drivers of both stream community and biogeochemical processes. However, the interplay between community and biogeochemical responses under different flow regimes in streams is less understood. In this study, we investigated the structural and functional responses of periphyton and macroinvertebrates to different densities of the Mediterranean barbel (Barbus meridionalis, Cyprinidae) in two stream reaches differing in flow regime. The study was conducted in Llémena Stream, a small calcareous Mediterranean streamwith high nutrient levels.Weselected a reachwith permanent flow(permanent reach) and another subjected to flowregulation (regulated reach)with periods of flowintermittency. At each reach,we used in situ cages to generate 3 levels of fish density. Cages with 10 barbels were used to simulate high fish density (N7 indm−2); cages with open sides were used as controls (i.e. exposed to actual fish densities of each stream reach) thus having low fish density; and those with no fish were used to simulate the disappearance of fish that occurs with stream drying. Differences in fish density did not cause significant changes in periphyton biomass and macroinvertebrate density. However, phosphate uptake by periphyton was enhanced in treatments lacking fish in the regulated reachwith intermittent flow but not in the permanent reach, suggesting that hydrologic alteration hampers the ability of biotic communities to compensate for the absence of fish. This study indicates that fish density canmediate the effects of anthropogenic alterations such as flowintermittence derived from hydrologic regulation on stream benthic communities and associated biogeochemical processes, at least in eutrophic streams., This research was supported by the Spanish Ministry of Economy and Competitiveness (projects CGL2013-43822-R and CGL2016- 80820-R); the Government of Catalonia (ref. 2014 SGR 484 and CERCA Programme) and the University of Girona (ref.MPCUdG2016/120). David Almeida benefitted from a postdoctoral fellowship from the Generalitat de Catalunya (2013 BP_B00172) and Baigal-Amar Tuulaikhuu benefited from a doctoral fellowship from the European Commission (Erasmus Mundus Partnership “Techno II”, 372228-1- 2012-1-FR-ERA MUNDUS-EMA21).

Garcia-Berthou, E., Almeida, D., Benejam, Ll., Magellan, K., Bae, M.-J., Casals, F., Merciai, R. 2015. Ecological impact of inland fish introduced to the Iberian Peninsula. Ecosistemas 24(1): 36-42. Doi.: 10.7818/ECOS.2015.24-1.07 The Iberian Peninsula has a rich fauna of freshwater fish, with many endemics that are threatened. One of the threat causes is the introduction of exotic species or translocation of natives to new basins. In this paper, we review the ecological impacts of these introductions, from the genetic and individual to the community and global levels, primarily using studies from the Peninsula. Although the accumulated evidence is considerable, the ecological impact of most species and introductions has barely been studied and is probably much greater than is known.

Multimesh nylon gillnets were set in three Ebro Delta (North-East of Spain) lagoons to determine mesh selectivity for the inhabiting fish community. Each gillnet consisted on a series of twelve panels of different mesh size (ranging from 5.0 to 55.0 mm bar length) randomly distributed. The SELECT method (Share Each Length’s Catch Total) was used to estimate retention curves through five models: normal location, normal scale, gamma, lognormal and inverse Gaussian. Each model was fitted twice, under the assumptions of equal and proportional to mesh size fishing effort, but no differences were found between approaches. A possible situation of overfishing in the lagoons, where artisanal fisheries are carried out with a low surveillance effort, was assessed using a vulnerable species inhabiting these brackish waters as case study: the sand smelt, Atherina boyeri . The minimum size for its fishery has not been established, thus remaining under an uncontrolled exploitation situation. Therefore, a Minimum Landing Size (MLS) is proposed based on sexual maturity data. The importance of establishing an adequate MLS and regulate mesh sizes in order to respect natural maturation length is discussed, as well as, the proposal of other measures to improve A. boyeri fishery management.

The knowledge of capture efficiency and side effects of electrofishing is essential for research and monitoring of stream fish populations. Differences amongst electrofishing crews have hardly been investigated and are particularly important given the on-going implementation of the Water Framework Directive and wide-ranging exchange of data worldwide. We aimed to assess fish catchability in Mediterranean streams and to compare four electrofishing crews (with minor differences in gears used) and their short-term effects on fish populations. In eight different sites, we compared two adjacent stations, one sampled with conventional single-pass catch-effort data and the other closed with block nets and with four-pass removal estimates. We used a Williams' cross-over design to estimate the independent effects of repeated sampling in four consecutive days, site and crew and also to assess a potential carry-over effect. We modelled capture probability and estimated population size using program MARK and an information-theoretic framework. Our results show that electrofishing was generally efficient in these reaches, with 50-100% of the species and of 40-60% of the individuals captured in a single pass. The CPUE was significantly higher at sites blocked with nets than at open sites, but observed richness was not significantly different. Capture probability was generally not constant along removal passes and increased with fish size. Observed fish richness and species composition did not depend on electrofishing crew and fishing day and there was no significant carryover effect. There were, however, significant differences in single-pass CPUE estimates amongst electrofishing crews, after accounting for other sources of variation. There was also a significant carry-over effect, surprisingly with increasing fish captured after fishing by specific crews. Overall, our results suggest that although capture probability depends heavily on a number of factors (such as species, size, and sampling site) and needs careful consideration, the effect of electrofishing crew is negligible for assessment of species richness and composition but considerable for fish abundance This study was financially supported by the Catalan Water Agency (project Ibicat2) and the Spanish Ministry of Science (projects CGL2009-12877-C02-01 and Consolider-Ingenio 2010 CSD2009-00065)

The spatial distribution of closely related individuals can be inferred from genetic data and provides valuable information about dispersal patterns and gene flow contributing to the population genetic structure of organisms. Here, we analyzed family distribution of brown trout Salmo trutta in the uppermost reaches of the Mediterranean Son River basin by genotyping nine microsatellite loci. Population structure suggested a model of two units heavily affected by hatchery introgression superimposed on a hydrographic pattern. We observed kin-biased spatial distribution, implying limited dispersal of related fish, probably favored by severe climate conditions in this system. However, downstream dispersal was observed for some large adult fish. Variance in family size defined small estimates of effective population sizes (Ne) in all streams. Comparison of estimates by several methods indicated that factors other than variation of family size are responsible for such low values. The population structure in the Son River basin is, then, represented by interconnected locations in which dispersion of the fish is probably conditioned by oscillations in water discharge, particularly the extremely low water flow during summer. Stream discharge variation could also be related to the flexibility of the mating system. Such characteristics make populations especially vulnerable to stocking and to any other potential effects.

The life-history tactics of the stone loach Barbatula barbatula were studied in a Mediterranean-type climate stream (Matarranya River) located in the Ebro River basin (north-east Spain). Maximum observed ages were 2+ years in both sexes (1% of individuals), although only 0+ and 1+ year age groups were well represented. It is the lowest longevity reported for this species in its entire distribution. The seasonal growth period started in June and continued until November, but the pattern observed was different to northern populations. Barbatula barbatula in the Matarranya River was a multiple spawner, releasing small batches of oocytes between April and June. The fecundity of females was higher and the size of oocytes smaller in 1984 than in 1985. The relative fecundity (number of ripening and ripe oocytes g(-1) of fish) was lower than in northern European populations. The role of the particular environmental conditions of a Mediterranean stream was discussed in relation to the life-history tactics of B. barbatula.

A spatially based approach was used to analyse the response of fish-based metrics to human impacts in the Iberian Peninsula. A fish-based typology was established that distinguished one salmonid type (fish assemblages dominated by Salmo trutta fario L.), two mixed types (S. trutta fario associated with different cyprinids) and six cyprinid types (dominated by different species of barbel (Barbus spp.), nase (Chondrostoma spp.) or chub (Leuciscus spp.)). These types broadly correspond to different forms of ecosystem functioning, ranging from the cold, northern and high altitude sections to warmwater, lowland and southern sections. Twenty metrics were identified that responded to disturbance - four to 14 per fish type. The highest correla- tions were )0.795 for abundance of Squalius sp. and segment (localised) disturbance and 0.754 for abundance of limnophilic specimens and water quality disturbance. Disturbance of segment, habitat and hydrological regime yielded more metric responses in western Iberian fish types, while that of habitat and water quality gave more in north-eastern Iberian fish types. Global (catchment scale) disturbance generally gave more responsive metrics and higher correlations than partial disturbances. All guilds were represented and a number of metrics were responsive across fish types - namely native species, alien abundance, water column (natives), eurytopic and invertivorous (natives). However, several metrics were only reactive in one or a few types, such as benthic and S. trutta fario in north-western mixed fish type. Different trends in metric reaction occurred for total abundance in north-western mixed fish type, and for eurytopic and phytophilic (natives) in the north-eastern fish types.

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.

Freshwater ecosystems are among the most affected by anthropogenic disturbances, and fish have several advantages for monitoring them, such as the response at larger temporal and spatial scales and its visibility to the society. This chapter summarizes our experience in developing fish-based indices in Catalonia. We describe some differences observed among crews in electrofishing captures and habitat assessments. We also analyzed the suitability of a single pass for conventional monitoring in the region and differences in capturability among sites and species by comparison with multiple passes and block nets. Furthermore, we summarize the results of two contrasting approaches, a site- and a type-specific one (IBICAT2a and IBICAT 2b) applied to Catalan rivers. The site-specific was not successful and further data are needed for its improvement. A protocol for the computation of a type-specific, multimetric index (IBICAT2b) is given. The IBICAT2b fish index uses 4–8 metrics depending on river type and has been validated with environmental pressures both throughout Catalonia and the whole Ebro River basin. An Excel file is also given as an online supplementary material for the computation of this fish index.

Abstract In complex aquatic ecosystems, intraspecific competition for food can evolve into dietary differences related to body size, gender, capture ability, and habitat use. The diet of the viperine snake, Natrix maura, an aquatic predator which forages on fish and amphibians, has been studied in parallel with food availability in a small locality of the Matarranya River (NE Spain). Fish abundance values in this Mediterranean river, which hosts one of the highest rates of fish diversity in Europe, were estimated through electrofishing. Natrix maura fed on four of the ten fish species available and captured the only amphibian detected. Three of these fishes were the most abundant species in the river. The fourth fish was the river blenny, a small and rare benthonic species of which the males protect eggs laid under stones at the bottom of the river during reproductive periods. This behaviour makes it easy prey for N. maura. However, the river blenny was caught mostly by small- and medium-sized snakes, while larger individuals, particularly females, fed on larger and more mobile prey that were more abundant and energetically more profitable. Similar diet differences according to size and gender have been described in other water snakes. We discuss whether this coincidence may be related to the great tropic availability in aquatic environments for fish-eating snakes.

Bioassessments are used to measure system health and assess disturbance. While fish-based freshwater bioassessments are cost-effective and perform well in speciose systems, such bioassessments remain difficult to implement in species-poor Mediterranean regions. Population size structure metrics may provide meaningful biological information where depauperate communities preclude the richness and composition measures generally used. We focus our assessments of population size structure responses to anthropogenic perturbation on one of the most widespread native stream fish (Squalius laietanus). We explore a number of population size statistics as metrics for a Mediterranean region, where current bioassessments perform poorly. Our sampling encompassed 311 sites across Catalonia (NE Spain) where we characterized anthropogenic perturbation using a summary of impacts, including local data on stream condition and landscape indicators of degradation, via a principal component analysis. Anthropogenic perturbation in streams was collinear with altitudinal gradients and highlights the importance of appropriate statistical techniques. Of the population size structure metrics explored, average length was the most sensitive to anthropogenic perturbation and generally increased along the disturbance gradient. Although we expected to find consistent changes in variance, kurtosis, and skewness, the observed relationships were weak. River basin mediated responses suggest the importance of environmental landscape factors. The unexpected increases of mean S. laietanus body size with anthropogenic perturbation, strong effects of river basin, collinearity with spatial gradients and the species-specific nature of responses preclude the direct application of size structure in freshwater bioassessments. Although its application in fish-based freshwater bioassessments appears difficult, population size structure can provide insights in species-specific applications and management Additional financial support was provided by theSpanish Ministry of Science (projects CGL2009-12877-C02-01 andConsolider-Ingenio 2010 CSD2009-00065)

1. North-eastern Spain is a hot spot for the introduction of alien fish species, and its native fish fauna is one of the most endangered worldwide. We used an extensive data set from 2002 to 2003 and historical information from the area to characterize fish diversity and establish conservation priorities in river catchments. 2. Diversity indices were used to characterize fish diversity at the basin scale. An index of conservation status was applied for each species, which considers the occurrence, abundance and endemicity of each taxon. We used indirect ordination methods to test the relationship among basin features and to identify those variables most correlated with each other. To identify physical, biotic and environmental characteristics that seem to make a basin particularly susceptible to invasion, we performed a step-wise multiple regression to examine the relationship between the number of native, translocated and introduced fish species (including the original native species richness of each basin), and landscape variables. 3. Over a period of approximately 50 years, the mean range size of native fish species has decreased by 60%. The greatest decline occurred in Gasterosteus gymnurus, Anguilla anguilla and Salaria fluviatilis, for which species over 75% of the original distribution area has been lost. The species with the highest conservation index were Gasterosteus gymnurus and Salaria fluviatilis. 4. Basin area and the catchment type explained 70% of variation in native species richness, whereas the number of dams and basin area accounted for more than 80% of variation in the number of introduced species. 5. The original native species richness and the number of introduced species at basin scale were not related, and thus there was no evidence of “biotic resistance” to invasion. The restoration of natural hydrologic processes and the development of specific management tools to protect native species, such as the prioritization of areas for fish conservation and the eradication of local populations of exotic species, are required to restore native fish fauna in these catchments.

[EN] Mediterranean river systems are characterised by more diverse fish assemblages and regional ecological processes compared with the rest of Europe. A data set from Mediterranean France, Iberia and Greece ( 2000 sites) was used to describe the characteristics of fish assemblages, explore their responses to anthropogenic disturbance and analyse the implications for river quality assessment. There was a southwards decline in species richness per site, but endemicity and proportion of alien species increased. Sites in the eastern Mediterranean had higher endemicity, lower site richness and lower number of alien species than sites in western Mediterranean Europe. Assemblage composition differed between Mediterranean sub-regions, but was dominated by three major fish types: a salmonid fish type common throughout the study area and two cyprinid-dominated fish types (in some sub-regions, Salmo trutta L. is present but not numerically dominant), corresponding to a gradient in hydrological and temperature regimes. Metric responses to perturbation were compared with those found at the European (larger scale) and basin (smaller scale) levels. Overall metric response was weaker in this Mediterranean application. The best responses to human pressure were usually obtained with abundance-based metrics and included the contribution of naturalised alien species. Some widespread alien species contributed to the response to anthropogenic alteration (notably Cyprinus carpio L. and Lepomis gibbosus (L.))., We thank Stefan Schmutz and his team for the coordination of the European FAME project (financed by the European Union, contract no. EVT1-CT-2001- 00094); his encouragement and support made the development of the Mediterranean data set possible. We are also indebted to all people that have taken part in the data collection and graciously agreed to share their information.

Aim :To analyse the patterns in species richness and endemism of the native European riverine fish fauna, in the light of the Messinian salinity crisis and the Last Glacial Maximum (LGM). Location :European continent. Methods :After gathering native fish faunistic lists of 406 hydrographical networks, we defined large biogeographical regions with homogenous fish fauna, based on a hierarchical cluster analysis. Then we analysed and compared the patterns in species richness and endemism among these regions, as well as species-area relationships. Results :Among the 233 native species present in the data set, the Cyprinidae family was strongly dominant (> 50% of the total number of species). Seven biogeographical regions were defined: Western Peri-Mediterranea, Central Peri-Mediterranea, Eastern Peri-Mediterranea, Ponto-Caspian Europe, Northern Europe, Central Europe and Western Europe. The highest regional species richness was observed for Central Peri-Mediterranea and Ponto-Caspian Europe. The highest endemic richness was found in Central Peri-Mediterranea. Species-area relationships were characterized by high slope values for Peri-Mediterranean Europe and low values for Central and Western Europe.Main conclusions :The results were in agreement with the "Lago Mare" hypothesis explaining the specificity of Peri-Mediterranean fish fauna, as well as with the history of recolonization of Central and Western Europe from Ponto-Caspian Europe following the LGM. The results also agreed with the mechanisms of speciation and extinction influencing fish diversity in hydrographical networks. We advise the use of the seven biogeographical regions for further studies, and suggest considering Peri-Mediterranean Europe and Ponto-Caspian Europe as "biodiversity hotspots" for European riverine fish.