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Funding 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)., 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 pot, European Commission, Fundación Biodiversidad, Nafarroako Gobernua, Fundación para la Ciencia y la Tecnología, Foundation for Science and Technology (Portugal), Depto. de Biodiversidad, Ecología y Evolución, Fac. de Ciencias Biológicas, TRUE, pub

This study was supported by the LIFE INVASAQUA project (Aquatic Invasive 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 supported specific actions into the LIFE INVASAQUA. J.M. Z.-M. is supported by a postdoctoral grant funded by the Spanish Ministry of Science and Innovation and the European Union NextGeneration EU/PRTR (FJC2021-046923-I). F.R. is supported by Foundation for Science and Technology through an individual contract (CEEC/0482/2020). I.B. and J.A.C. were funded by the Basque Government (IT1487-22). 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). C.C. was supported by Portuguese national funds to the CEG/IGOT Research Unit (UIDB/00295/2020 and UIDP/00295/2020), through FCT - Fundação para a Ciência e a Tecnologia, I.P. F.C.A, was funded by CEF, a research unit of FCT, Portugal (UIDB/00239/2020). A.A. H.-R. was supported by a predoctoral grant from the University of Murcia (R-483/2023)., Aquatic ecosystems are particularly vulnerable to the introduction of non-indigenous species (NIS), leading to multi-faceted ecological, economic and health impacts worldwide. The Iberian Peninsula comprises an exceptionally biodiverse Mediterranean region with a high number of threatened and endemic aquatic species, most of them strongly impacted by biological invasions. Following a structured approach that combines a systematic review of available information and expert opinion, we provide a comprehensive and updated multi-taxa inventory of aquatic NIS (fungi, macroalgae, vascular plants, invertebrates and vertebrates) in Iberian inland waters. Moreover, we assess overall patterns in the establishment status, introduction pathways, native range and temporal introduction trends of listed NIS. In addition, we discuss the legal coverage provided by both national (Spanish and Portuguese) and European NIS regulations. We inventoried 326 aquatic NIS in Iberian inland waters, including 215 established, 96 with uncertain establishment status and 15 cryptogenic taxa. Invertebrates (54.6%) and vertebrates (24.5%) were the groups with the highest number of NIS, with Arthropoda, Mollusca, and Chordata being the most represented phyla. Recorded NIS originated from diverse geographic regions, with North and South America being the most frequent. Vertebrates and vascular plants were mostly introduced through intentional pathways (i.e. release and escape), whereas invertebrates and macroalgae arrived mostly through unintentional ways (i.e. contaminant or stowaway). Most of the recorded NIS were introduced in Iberian inland waters over the second half of the 20th century, with a high number of NIS introductions being reported in the 2000s. While only 8% of the recorded NIS appear in the European Union list of Invasive Alien Species of Union concern, around 25% are listed in the Spanish and Portuguese NIS regulations. This study provides the most updated checklist of Iberian aquati, European Commission, Ministerio de Ciencia, Innovación y Universidades (España), Gobierno de Navarra, Eusko Jaurlaritza, Portuguese Foundation for Science and Technology, Depto. de Biodiversidad, Ecología y Evolución, Fac. de Ciencias Biológicas, TRUE, pub

Aquatic ecosystems are particularly vulnerable to the introduction of non-indigenous species (NIS), leading to multi-faceted ecological, economic and health impacts worldwide. The Iberian Peninsula comprises an exceptionally biodiverse Mediterranean region with a high number of threatened and endemic aquatic species, most of them strongly impacted by biological invasions. Following a structured approach that combines a systematic review of available information and expert opinion, we provide a comprehensive and updated multi-taxa inventory of aquatic NIS (fungi, macroalgae, vascular plants, invertebrates and vertebrates) in Iberian inland waters. Moreover, we assess overall patterns in the establishment status, introduction pathways, native range and temporal introduction trends of listed NIS. In addition, we discuss the legal coverage provided by both national (Spanish and Portuguese) and European NIS regulations. We inventoried 326 aquatic NIS in Iberian inland waters, including 215 established, 96 with uncertain establishment status and 15 cryptogenic taxa. Invertebrates (54.6%) and vertebrates (24.5%) were the groups with the highest number of NIS, with Arthropoda, Mollusca, and Chordata being the most represented phyla. Recorded NIS originated from diverse geographic regions, with North and South America being the most frequent. Vertebrates and vascular plants were mostly introduced through intentional pathways (i.e. release and escape), whereas invertebrates and macroalgae arrived mostly through unintentional ways (i.e. contaminant or stowaway). Most of the recorded NIS were introduced in Iberian inland waters over the second half of the 20th century, with a high number of NIS introductions being reported in the 2000s. While only 8% of the recorded NIS appear in the European Union list of Invasive Alien Species of Union concern, around 25% are listed in the Spanish and Portuguese NIS regulations. This study provides the most updated checklist of Iberian aquati

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 pot

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 pot

Risk analyses for invasive species often assume that the characteristics of future invaders will resemble those already successful, but these features may change. Here, we use data from more than 3,500 fish sampling events, sequencing of mitochondrial and nuclear genes and analyses of several traits describing non-native fish to describe the irruption and rapid expansion of non-native loaches in Catalonia, north-east Iberian Peninsula, and framing this surge in the knowledge of previous invasions. We report the establishment of at least five (Cobitis bilineata, Misgurnus anguillicaudatus, Misgurnus bipartitus, Paramisgurnus dabryanus, and a yet undescribed Barbatula species) non-native loach species in Catalonia, most of which are currently spreading. Furthermore, one of the two regionally native loach species (Cobitis paludica) has been introduced and is spreading through river basins where it is not native. Genetic analyses were fundamental to understand loach invasions, by clarifying specific statuses, identifying the origin of non-native populations and/or detecting independent introduction events. Genetic results also highlighted the unresolved taxonomy of loaches, particularly for European Barbatula. Loaches are recent, diverse, and successful invaders whose traits differ from those of most previously established invasive fish species, signalling potential weaknesses of prevention of biological invasions based on prohibited species lists. We call for the development of more flexible management tools (e.g. based on fish traits and not only on species identities) and prioritising prevention and rapid responses to new introductions.

One of the objectives of LIFE INVASQUA project is to develop tools that will be more efficient the Early Warning and Rapid Response (EWRR) framework for Invasive Alien Species in the Iberian Peninsula. Horizon scanning for high-risk IAS is basic in implementing measures to reduce new invasions, developing Alert lists, and to focus effort in the species already established, for instance making a Black list. We developed a trans national horizon scanning exercise focused on inland waters of Spain and Portugal in order to provide a prioritized lists (Black list and Alert list) of aquatic IAS that may pose a threat to aquatic ecosystems and socio economic sectors in the future. We followed a step approach of existing information about IAS (Plants, Freshwater Invertebrates, Estuarine Invertebrates and Vertebrates; 127 established taxa in Black list; 90 non established taxa in Alert list) combining with an expert scoring of prioritized taxa. IAS established in the Iberian aquatic system consistently highlighted as the worst included vertebrates (e.g. Cyprinus carpio, Gambusia holbrooki, Silurus glanis), freshwater and estuarine invertebrates (e.g. Procambarus clarkii, Dreissena polymorpha, Pacifastacus leniusculus, Ficopomatus enigmaticus, Callinectes sapidus, Corbicula fluminea) and plants (e.g. Eichhornia crassipes, Azolla filiculoides, Ludwigia grandiflora). Amongst taxa not yet established (Alert list), expert pointed to Perna viridis, Hydroides dirampha, Dreissena bugensis, Procambarus fallax f. virginallis, Perccottus glenii with higher risk of invasion, ecological and socioeconomic impacts. Over 20.6% of the taxa in the preliminary black list received no votes (no prioritization) by experts, 17.8% in the innitial alert list. Our horizon scanning approach is inclusive of all-taxa, prioritizes both established and emerging biological threats across trans-national scales, and considers not only the ecological impact, but also potential direct economic consequences as

1. Introduced fish are a widespread ecological threat in originally fishless high mountain lakes. However, basic distribution data are largely missing for most high mountain regions. 2. Using time-consuming standard methods (e.g. Nordic standard fishing nets) to assess fish distribution and relative densities at a relevant spatial scale can be impracticable, because of the large number of high mountain lakes. To overcome this problem, alternative rapid monitoring methods would be helpful. 3. Visual encounter survey (VES) is a candidate method that enables observing fish from the shoreline. It takes only minutes to implement and is already widely used for amphibian monitoring in high mountain lakes and ponds. VES was evaluated as a method for monitoring introduced salmonids and cyprinids (the most widespread fish families) in 52 high mountain lakes. 4. The probability of detecting both families by VES rapidly approaches 100% as the relative densities of fish increase, and false absences are restricted to populations living at low relative densities. VES also provides simple indications about fish relative densities, distinguishing between high-density and low-density populations. 5. As VES usually does not enable fish species identifications, we propose VES as a useful method to describe large fish distribution inventories, not needing high taxonomic detail, but necessary for planning large-scale conservation measures.

In alpine biogeographic regions, aquatic and semi-aquatic habitats are important biodiversity reservoirs and habitats for species of community interest, but they are often threatened by multiple factors. The conservation state of protected habitats and species in the EU is expected to worsen as long as no actions or conservation strategies are implemented. LIFE RESQUE ALPYR aims to restore mountain aquatic habitats by improving the conservation of several target habitats/species in four Nature 2000 sites from the alpine biogeographical regions of the Pyrenees (in northeastern Iberian Peninsula) and the Alps (in northwestern Italy). The target habitats include eleven aquatic and semi-aquatic habitats, of which five are prioritary: high mountain lakes (HCIs 3110 and 3130), alpine and subalpine grasslands, heaths and meadows (HCIs 4020*, 6230*, 6410, and 6520), mires (HCIs 7110*, 7140, 7230, and 91D0*) and petrifying springs (HCI 7220*). The target species include native amphibians found either in both areas (Rana temporaria) or solely in the Pyrenees (Euproctus asper and Alytes obstetricans); the semi-aquatic mammal Galemys pyrenaicus living in Pyrenean streams and lakes; and seven insectivorous bats, including Barbastella barbastellus, Myotis myotis, and Plecotus macrobullaris, which are present in the Pyrenees and the Alps, and Rhinolophus hipposideros, Myotis blythii, Myotis bachsteinii, and Nyctalus lasiopterus from the Pyrenees. The target habitats and most of the target species have naturally fragmented distributions, occurring in small areas of the European alpine biogeographic zone, and are affected by anthropogenic pressures. The introduction of trout or minnows in most alpine lakes caused the disappearance of native amphibians and invertebrates at local and landscape scales, indirectly affecting aquatic mammals and terrestrial species, such as bats, that rely on aquatic insects for feeding. Minnows can also cause the strong eutrophication of lakes, leading t

1. Invasive alien species are among the most important threats to biodiversity. Plans for their eradication have been implemented worldwide but estimating residual population size and eradication probability to assess removal success is complicated by the imperfect detection of residual individuals. 2. Most methods to assess residual abundance and eradication probability rely on the often unrealistic assumption that a population is closed to mortality and recruitment processes during the implementation of removal actions. We extended existing removal models and developed a novel analytical approach to estimate residual population size and derive eradication probability in open populations, while accounting for multiple removal methods. 3. We apply this approach to 20 eradication projects in Europe and the United States that used mechanical methods to return high mountain lakes to their original fishless condition. 4. The new removal model incorporates i) a mechanistic description of the ecological process underlying survival and recruitment probabilities during the eradication period, and ii) the use of multiple, concomitant removal methods (i.e., electrofishing, gillnetting, fyke-netting) at multiple sites simultaneously. 5. We used a subset of “control” lakes where eradication success was confirmed by more than 5 years of post-removal surveys to validate the model. For these lakes, eradication success, evaluated by whether the 95% Bayesian credible interval for estimated residual population size encompassed values of less than 2 individuals, was confirmed in 13 out of 15 lake-by-species case studies. In addition, the model correctly assigned an eradication probabilities equal to 0 for the eradications that are still in progress. 6. Synthesis and applications. Our study provides insights into the dynamics of fish populations subject to eradication in high mountain lakes of different countries. In addition, the analytical approach proposed accounts for demographic p

Se presenta una lista actualizada de las especies exóticas que se encuentran en etapa de establecimiento o de propagación de la invasión en aguas continentales de la península ibérica. La lista está basada en la evaluación sistemática de los datos en colaboración con un amplio equipo de expertos de España y Portugal. Esta lista de actualización es un instrumento de apoyo importante para la aplicación del Reglamento de la Unión Europea (UE) sobre las especies exóticas invasoras (EEI) y también proporciona una base objetiva para el examen de su aplicación. En última instancia, la información incluida puede utilizarse para supervisar el cumplimiento del objetivo de la Estrategia de la UE sobre diversidad biológica hasta 2030 para combatir las EEI, pero también para la aplicación de otras políticas de la UE con requisitos sobre especies exóticas, como las Directivas de Hábitats y Aves, la Directiva Marco sobre la Estrategia Marina (DMEM) y la Directiva Marco del Agua (DMA). Esta publicación es un informe técnico del Proyecto Europeo LIFE INVASAQUA (LIFE17 GIE/ES/000515). Ha sido redactado por un equipo de expertos en el marco del proyecto y tiene por objeto proporcionar apoyo, basado en pruebas científicas, al proceso de formulación de políticas europeas. La información científica aportada no implica una posición política de la Comisión Europea. Ni la Comisión Europea ni ninguna persona que actúe en nombre de la Comisión es responsable del uso que pueda hacerse de esta publicación.