This special issue of Management of Biological Invasions is dedicated to the late Professor Gordon H. Copp, a pioneer in invasion biology and recipient of the prestigious Doctor of Science title for his exceptional scientific contributions. Over his career, Gordon met the “gold standard” of scientific excellence through his peer-reviewed publications, successful research funding, international collaborations, and leadership roles. In the early 2000s, Gordon shifted his main focus from fish conservation biology to invasion biology, where he significantly advanced the field, particularly in non-native species risk analysis. Alongside his career-long collaborator Lorenzo Vilizzi, he developed decision support tools for risk identification, including the Freshwater Fish Invasiveness Screening Kit and “ISK” siblings, and its successor, the Aquatic Species Invasiveness Screening Kit (AS-ISK), which has been used globally to assess the risk of non-native aquatic organisms. Gordon’s work laid the foundation for the European Non-native Species in Aquaculture Risk Analysis Scheme, influencing policies and practices worldwide. This special issue features contributions from some of Gordon’s closest collaborators and mentees, who explore a wide range of topics in invasion biology. Highlights include updated methodologies for risk screening with the AS-ISK, case studies from diverse geographic regions, and discussions on the socio-economic impacts of invasive species. This special issue also introduces a new screening toolkit, which addresses gaps in current tools for risk identification. Collectively, these studies honour Gordon’s legacy by continuing to advance understanding and management of biological invasions, ensuring his influence endures for future generations of scientists. We hope this special issue serves as a valuable reference for researchers and practitioners in the field and that Gordon would have appreciated the quality and scope of the contributions as a testament to his lasting impact.

In invasion biology, terminological frameworks contribute to the improvement of effective communication among scientists, stakeholders, and policy-makers. This is important not only for informing policy decisions but also for engaging the broader public in understanding the risks associated with biological invasions. Meanwhile, the role of non-English languages in advancing knowledge in invasion biology has gained momentum in recent years. Building on the seminal contributions in this scientific discipline by Professor Gordon H. Copp, this paper examines the provision of three key terms defining species invasiveness in 28 non-English languages. We first refine the standardized terminology for invasion biology recently proposed in a review paper by defining the three non-redundant terms “non-native species”, “established species”, and “invasive species”. Through a comparative analysis of the equivalent of these terms in the 28 non-English languages, as contributed by our panel of invasion biologists and native speakers, with those in the reference review paper, and following the diffusion-of-English versus ecology-of-language paradigms, we identify discrepancies and nuances reflecting the dynamic nature of terminology in invasion biology. While some languages showed consensus in terminology, others differed due to either the avoidance of a culturally or politically laden term for “non-native” or the achievement of greater precision in meaning. Our findings highlight the requirement for clear and precise terminology in invasion biology and suggest the adoption of multidisciplinary approaches to reach consensus and facilitate communication amongst scientists, policy-makers, and the general public in a globally interconnected and rapidly changing world. This will enhance international collaboration and accelerate knowledge exchange, leading to more effective management of biological invasions.

As a result of the increasing threats posed by non-native species invasions, there has been a rise in the demand for decision support tools that can more efficiently identify those non-native species likely to become invasive. As part of the risk screening (first) step in the environmental risk analysis process, three multilingual decision support tools are currently available for the screening of aquatic and terrestrial organisms: the Aquatic Species Invasiveness Screening Kit (AS-ISK), the Terrestrial Animal Species Invasiveness Screening Kit (TAS-ISK) and the Terrestrial Plant Species Invasiveness Screening Kit (TPS-ISK). Here, we describe the recent improvements to the questionnaire that forms the base of these second-generation Weed Risk Assessment-type tools. We subjected the AS-ISK and TAS-ISK questionnaires to a thorough revision and extended these improvements for the development of the TPS-ISK. Overall, this involved an improvement of the AS-ISK and TAS-ISK questionnaires, an alignment of the questionnaires across the three toolkits, and the translation of the three resulting questionnaires in all 30 non-English languages supported by the toolkits. Given the most extensive usage of the AS-ISK and, in perspective, of the recently released TAS-ISK and TPS-ISK, it is timely to provide researchers and decision-makers in the field of invasion biology with a suite of updated toolkits designed to streamline and improve the risk screening process. These enhancements will be crucial for the delivery of reports to stakeholders and decision-makers also in the languages supported by the toolkits as applicable, and in line with the ecology-of-language paradigm at the base of the toolkits’ multilingual interface development.

Risk screening is a rapid, cost-effective means of gaining information on risk for large numbers of nonnative species. Professor Gordon H. Copp used the Australian Weed Risk Assessment as a template for creating the Invasiveness Screening Kit (ISK) family of screening tools, including the Fish Invasiveness Screening Kit (FISK and FISK v2) and the Aquatic Species Invasiveness Screening Kit (AS-ISK). These tools are effective and practical with numerous applications worldwide. Here we show the influence of Prof. Copp on U.S. management of nonnative aquatic species. We review applications of ISK tools in the USA, present three case studies of applications to U.S. management, and describe management challenges and decision-making for U.S. applications. The ISK tools have proven to be versatile and transparent across a wide range of climate zones and geography. Published applications contained 337 species × risk assessment area combinations, including 102 marine invertebrates, 6 tunicates, 168 freshwater fishes, 1 brackish fish, 58 marine fishes, 1 amphibian, and 1 bird. The risk assessment areas have ranged from the conterminous USA to regions within states. Basic management decisions supported by these applications include hazard identification, initial risk estimation, and the need for additional assessment. More specific management decisions included commercialization of genetically modified organisms (GMO), national versus subnational risks, dangerous species versus invasive species, established medium-risk species with minimal impacts, risk screens in horizon scanning, and others. These cases involved federal and state agencies and the private sector. Applications in the USA contributed innovations to the field, such as the development of FISK v2 and the first application to a GMO. Professor Copp’s contributions to U.S. management have been extraordinary, influencing decisions by agencies and industry, benefitting natural resource protection, and fostering positive economic impacts.

The Philippines is a mega-biodiversity country hosting a vast number of aquatic species of which most are endemic. With over 7,100 islands making up its territory, the Philippines are home to a remarkable array of fish species. These play a vital role in enriching the country's inland waters biodiversity and some of them are of high economic and commercial value. However, this extremely rich biodiversity is on the brink of collapse. Research in the Philippines has primarily focused on marine and terrestrial ecosystems, highlighting a significant gap in the study of inland waters and its freshwater fishes. In total, 374 freshwater fish species belonging to 29 orders and 78 families have been documented in the Philippines. This large number of fish species faces high extinction risks due to various human-induced impacts including habitat destruction, overfishing and the presence of introduced species. This study investigates the risk of invasiveness of all 64 introduced freshwater fish species currently present in the Philippines. Of these species, 65.6% and 70.3% were ranked as carrying a high or very high risk of invasiveness under current and future climate conditions, respectively. The highest risk species were goldfish Carassius auratus, Indonesian snakehead Channa micropeltes, largemouth black bass Micropterus salmoides, pirapitinga Piaractus brachypomus, vermiculated sailfin catfish Pterygoplichthys disjunctivus and Amazon sailfin catfish Pterygoplichthys pardalis. Given the high conservation value of Philippine freshwater ecosystems, efforts are needed from stakeholders and environmental managers in the mitigation and prevention of the detrimental impacts of the invasive fish species already present, and preventative measures are required to counteract the introduction of any additional non-native species. The results of this study, which represents the first comprehensive risk screening for a specific group of organisms in a country, will serve as a foundation for developing shared regulations to control the international trade of the non-native fish species at higher risk of invasion.

Invasive species risk assessment tools are a vital means of identifying taxa likely to be introduced and cause adverse effects within a specified area, allowing for the preparation of targeted management strategies. Following the first report of the shimofuri goby (Tridentiger bifasciatus) in Europe, a risk assessment was undertaken for this species for Great Britain using the Aquatic Species Invasiveness Screening Kit (AS-ISK). This was achieved by the completion of two risk screenings, one undertaken for England and Wales, and another for Scotland. The results of this assessment place the shimofuri goby in a category of medium risk for both assessed areas. The shimofuri goby’s adaptable nature and ability to change its reproductive strategy in response to climatic conditions increase the likelihood of the species persisting and proliferating within the area after introduction. However, the species’ inability to survive in marine salinities reduced the score for likelihood of its introduction, and its small size and generalist nature coupled with a lack of available evidence made the prediction of specific impacts difficult. In addition, the extent of suitable habitat for this species is likely to expand throughout Great Britain under predicted climate change, thus increasing the risk of its establishment and potential impacts.

In the Western Balkans, fishery management and legislation do not recognize the high molecular diversity of native brown trout. For this reason, stocking of streams relies on brown trout of non-native origin. In recent years, there have been new findings about the life-history features, dispersal and molecular characterisation of nominal taxa of brown trout in the Western Balkans. This has prompted to a re-evaluation of their risk of invasiveness in the region. In this study, based on a screening of six non-native lineages of brown trout, four lineages were ranked as high risk and two as medium risk of invasiveness under current climate conditions, whereas one lineage was ranked as high risk and the other five as medium risk under predicted global warming scenarios. Variation in scores and risk outcomes was related to life-history traits differing among lineages, with most pronounced differences in dispersal mechanisms. The results of this study point to the need for improvement of relevant legislation in several sectors of fishery management. Management strategies should aim to mitigate the conflicts arising among stakeholders, which contribute to the deterioration of the native traits of brown trout stocks throughout the Western Balkans.

Non-native species risk analysis is a dynamic process that requires periodic review and revision. In this study, we investigated changes in the risk ranks of the 69 non-native freshwater fish species in England and Wales previously screened with the Fish Invasiveness Screening Kit using its successor, the Aquatic Species Invasiveness Screening Kit (AS-ISK). Our objectives were to assess shifts in species risk ranks, evaluate the implications of transitioning to the AS-ISK, and integrate climate change predictions into the screenings. Re-screening revealed several changes, with eleven species re-categorized from non-invasive to invasive and one from invasive to non-invasive, and with 18 species changing their risk ranks. Climate change projections influenced outcomes, with 40 out of 41 high-risk species maintaining such status when accounting for this component. The re-screening process implemented in this study emphasizes the importance of updating protocols to incorporate new data and climate change projections for more accurate risk screening. Analysis showed varied responses to climate change among species, with implications for management strategies. Salmonids exhibited nuanced responses, suggesting the need for tailored management approaches. Confidence levels were generally medium, highlighting the importance of continual refinement. Our study underscores the necessity of regularly updating non-native species risk screenings and follow-up assessments to account for newly available literature information. By integrating new data and climate change scenarios, the effectiveness of management strategies can be enhanced with the aim of safeguarding aquatic ecosystems and their biodiversity. Further research should focus on refining the entire risk analysis process and understanding species responses to changing environmental conditions to inform proactive management approaches.

Risk analysis of non-native species invasions is one of the main challenges currently faced by both scientists and environmental managers. In this study, the three risk screening toolkits Harmonia+, Aquatic Species Invasiveness Screening Kit (AS-ISK) and Canadian Marine Invasive Screening Tool (CMIST) were used in conjunction to evaluate the risk of invasiveness of eight non-native crayfish species (three extant already present in the risk assessment area and five horizon, not yet reported, but likely to arrive in the near future) for Lake Maggiore (Northwest Italy). Based on the toolkit-specific risk scores for each species and their final ranking according to the thresholds set for each toolkit: 1) Harmonia+ ranked five species with a medium-risk level of invasiveness and three with a low-risk level; 2) AS-ISK ranked all species as high risk; 3) CMIST ranked six species as high risk and two as medium risk. By combining the risk scores from the three toolkits and setting an ad hoc threshold, extant horizon calico crayfish Faxonius immunis, spinycheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, red swamp crayfish Procambarus clarkii and marbled crayfish Procambarus virginalis were ranked as high risk, whereas horizon Australian red claw crayfish Cherax quadricarinatus, yabby Cherax destructor and Danube crayfish Pontastacus leptodactylus were ranked as medium risk. It is anticipated that the findings of this study will help inform managers about the proper implementation of non-native species management strategies for the Lake Maggiore watershed.

Largemouth bass Micropterus nigricans has caused a wide range of invasive impacts and is listed among the top 100 of the World’s Worst Invasive Alien Species by IUCN. Yet it has been widely introduced around the world due to sport fishing needs and its importance for aquaculture. It also has been promoted most vigorously in the past five years in China, where the production of M. nigricans exceeded 90% of the total production of perches in 2019. In this study, the invasion risk of M. nigricans was assessed using AS-ISK andfound to he high in the middle and lower reaches of the Changjiang River. The European Non-native Species in Aquaculture Risk Analysis Scheme (ENSARS) was therefore used to evaluate the full invasive risk of M. nigricans in the same area. The results suggest that M. nigricans carries an overall medium risk of invasion in China, with every module suggesting a medium risk. Confidence ranks for the overall scores fell into the range of 2.0–2.5, which suggests a high confidence level. This study is meant to be a trial for further use of the ENSARS scheme in China, especially for potential non-native aquacultural species.

Increasing global trade in agricultural and horticultural products coupled with climate change are amongst the main drivers of the global spread of non-native insect species. This trend has substantial impacts on agroecosystems and economies in general. The aim of this study was to screen non-native insect species for their risk of invasiveness in Croatian agricultural lands under current and future climatic conditions. The invasion risk of 18 extant and eight horizon species was determined with a high level of confidence. Of the 26 species screened, 65.4% and 92.3% were ranked as high (or very high) risk under current and future climate conditions, respectively. The results of this study are expected to help policy makers to prioritise the management of both extant and horizon non-native insect species and to assist decision-makers in identifying candidate species for comprehensive, follow-up risk assessment. It is anticipated that the present findings will also contribute to the refinement of national legislation to control and regulate more effectively the spread of non-native insect species in Croatia also accounting for changing climatic conditions.

To inform non-indigenous species management and policy decisions it is often necessary to have a prioritized list of species and screening tools frequently are used for this purpose. However, despite numerous tools available that typically evaluate aspects of the introduction, establishment, and impacts of potential invasive species, there are still gaps in the criteria used meaning that not all tools are fit-for-purpose. Further, incorporating uncertainty in a way useful to managers has proven problematic. This paper introduces the Non-Indigenous Species Screening Tool, which was developed to fill such gaps and address common limitations in previous tools for screening potentially invasive species. Using a series of questions organized into three separate modules examining steps in the invasion process combined with both ecological impacts and socioeconomic impacts, this tool provides a semiquantitative valuation of risk which explicitly incorporates uncertainty into the score. Further, recognizing the increasing importance of considering climate change when assessing invasion risk, this tool also incorporates a modifier for this. We applied this tool to both existing non-indigenous species and potential ones (N = 44 species) across different taxa (plant, invertebrate, and fish) for the Columbia Glaciated Freshwater Ecoregion using four assessors. The question scores across all species and assessors showed strong correlation and the tool was able to differentiate low to high-risk species across taxa for species that were both present and not yet present. This suggests this tool is not taxa specific and can easily be applied for a variety of purposes.

China has the world’s largest aquaculture production that partly benefits from the introduction of high-quality germplasm from both abroad and within the country. However, the rivers, lakes and reservoirs of China face a high risk of invasion by non-native freshwater fish associated with aquaculture. In this study, we used peer reviewed and grey literature in combination with a field survey to investigate the status, pathways, mechanisms and management of introduced freshwater fish for aquaculture in China. Production of introduced freshwater fish accounts for 8% of total aquaculture in China and is dominated by tilapia, bass, ictalurid, pirapitinga, salmon, trout and sturgeon. However, the escape of non-native fish resulting from unstrict farming management, fishery stocking and mercy release has been frequently reported. In total, 155 non-native freshwater fish species have escaped into natural waters. Among these species, 102 are aquacultural of which 59 translocated and 43 introduced from abroad. Introduced species have been mainly reported from southern China, whereas translocated species from the north and west of the country. Available data suggest that non-native fish associated with aquaculture have escaped into the main rivers of China. However, the real risk posed by non-native fish to native species and the ecosystem has been hardly evaluated due to the lack of basic information on population dynamics of non-native fish. Despite management strategies for non-native species having achieved substantial progress in recent years in China, development of a suitable transformation strategy for aquaculture to fulfil sustainable development goals remains challenging. Academia, government and stakeholders should work jointly to develop management strategies to mitigate the risks posed by non-native species in aquaculture.

Raw Water Transfer (RWT) schemes move large volumes of freshwater between separate waterbodies via complex infrastructure networks, and are a pathway of freshwater invasive non-native species (INNS) spread in most nations globally. Environmental regulators in England and Scotland have recently introduced progressive policies outlining requirements for pathway stakeholders to manage RWTs. This is a positive step; though no known management methods currently exist, and the development of effective methods will be a long and challenging process. Additionally, under the current policy, not all RWTs will have to be managed. Multilateral stakeholder collaboration and co-ordinated action is therefore needed to deal with the invasion risk posed by the ever-increasing number of RWTs. RWT information is disparate and difficult to access in Great Britain however, and the INNS management community remains generally unaware of the pathway. We therefore present information to illustrate the scale and prevalence of RWTs in England and Wales, and highlight that many of the approximately 162 major RWTs (>45 million litres/day) in England and Wales cross Water Framework Directive management catchments and river basins boundaries, and in some cases political borders. We discuss the consequent need to integrate RWTs into well co-ordinated surveillance and management plans at multiple scales, and explore options to improve information access and stakeholder collaboration, in support of improved management efficacy and the attainment of national INNS targets.

Reintroducing a species to an area where it is locally extinct may contribute to reestablishing the ecosystem. However, we show that such reintroductions can pose a risk to biodiversity by introducing hitchhiking invasive organisms together with the donor population. This risk was caused by more severe impacts of invasive organisms in the habitat of the donor population than the receiving environment. The freshwater resident Atlantic salmon (Salmo salar) in Sweden's River Klarälven perform feeding migrations to Lake Vänern. The upper part of the watershed, in Norway, lost its salmon population due to hydropower development that obstructed upstream migration. We conducted a risk assessment of the potential impacts on native ecosystems from invasive organisms associated with reintroducing Atlantic salmon into the Norwegian part of the watershed by importing adult salmon spawners. This assessment is crucial due to differences in the development of invasive organisms in the Swedish and Norwegian parts of the watershed. The risk of impacts was evaluated for invasive species, parasites, bacterial pathogens, and viruses that are present or likely present in the lower part of the watershed, or at risk of being introduced. We found a high risk of negative impacts associated with the parasite Gyrodactylus salaris, viral hemorrhagic septicemia virus (VHSV), Aphanomyces astaci causing crayfish plague, Renibacterium salmoninarum causing bacterial kidney disease, and Tetracapsuloides bryosalmonae causing proliferative kidney disease. In addition, 20 invasive species and pathogens were associated with a medium risk and three with a low risk. The case study contributes to a deeper understanding of how reestablishing locally extinct or diminished species can influence biodiversity conservation efforts and the health of aquatic ecosystems, underlining the importance of comprehensive planning in restoration projects. We highlight the importance of risk assessment of invasive species when considering the reintroduction of native species or dam removal.

Despite the growing literature on the topic of freshwater fish invasions, few studies have employed a comprehensive analysis of the stages characterizing the invasion process with reference to the invasion pathway. There is therefore a need to understand more fully invasion pathways to avoid incomplete and biased conclusions and to support adequate management strategies. This study aims to provide a complete analysis of the species traits and invasion history that are associated with the successful passage of an alien freshwater fish species through the invasion pathway stages in European river basins. To predict how likely a freshwater fish species moves from each stage of the invasion pathway (release, establishment, spread and impact) to the next, generalized linear mixed models were run, using 23 species traits and seven variables describing introduction history as predictors for 127 established alien freshwater fish species in Europe. The results showed that the release and spread stages were driven primarily by variables related to invasion history (i.e. the type and number of causes of introduction). The establishment stage was driven mainly by functional and ecological traits, while the impact stage was driven both by functional and ecological traits and invasion history. Identifying the main drivers of alien species success at each invasion stage is key to designing stage-specific target management actions and thus contributing to an effective control of alien populations.

In Tuscany (Central Italy), a population of the invasive alien red swamp crayfish Procambarus clarkii is present in Lake Romena, close to a national park, and threatens the conservation of the native white-clawed crayfish Austropotamobius pallipes complex. A field study was conducted to reduce the abundance of the P. clarkii population through intensive trapping activities and improve the effectiveness of catches using three different types of traps: two wire mesh traps (cylindrical and rectangular) and artificial refuge traps. The study also aimed at assessing the composition of the lake animal community, particularly the presence of crayfish predators (using eDNA), and the potential spread of P. clarkii outside the lake. The control activities conducted over two trapping seasons in 2022–2023 led to a decrease of at least 50% in the abundance index (Catch Per Unit Effort) of the crayfish population. Cylindrical traps caught more individuals, especially larger ones and males, with artificial refuge traps capturing relatively more females and smaller individuals. eDNA sampling highlighted the presence of a diversified community, mainly composed of alien species, and some crayfish predators (e.g. fish). The surveys conducted in the surrounding areas revealed the presence of P. clarkii downstream of the lake. Control activities using different types of traps should be maintained to decrease further the P. clarkii population abundance, while additional management activities should be carried out to halt the spread of the species outside the lake in order to prevent its further ecological impacts.