Nonindigenous aquatic species (NAS) present in trade can become costly invaders once introduced and established in a new environment. Preventing NAS introduction is considered the most effective strategy to avoid potential negative ecological, economic, and human health impacts associated with certain species. The United States government enacts regulatory prevention measures carried out by numerous federal agencies with designated authority over certain species, taxonomic groups, and pathways of introduction. We examined 18 case study species across eight taxonomic groups and eight pathways of introduction using a gap analysis approach to identify current gaps in regulatory prevention that may hinder the United States from achieving a more “ideal state” of management in which no NAS or pathways of introduction are unregulated. We found that outside of pathway regulations for ballast water and biofouling, the majority of amphibian, fish, reptile, crustacean, and mollusk species are subject to little to no regulation aside from a few specific species that are highly regulated. We also found large knowledge gaps surrounding the diversity of species and quantities of individual organisms introduced into the United States through the hitchhiking and cultural release pathways. We highlight that the current regulatory approach in the United States is a “blocklist” approach where a select list of species is disallowed as compared to an “allowlist” (approved list of species allowed only) or “conditional list” (between a “blocklist” and “allowlist”) used by Australia and New Zealand. Increased documentation of the diversity and quantities of NAS entering the United States and a better understanding of the contribution of the hitchhiking and cultural release pathways to NAS introductions could help inform regulatory prevention.

Ballast water is one of the main vectors for the introduction of exotic species to coastal ecosystems. The D-2 standard of the International Maritime Organization (IMO) sets limits to the permitted maximum concentration of living organisms in ballast water to prevent marine invasions. This study evaluated the compliance with the D-2 standard of the ballast water of ships arriving to Chilean ports in 2017. Ballast water samples were collected from twelve ships at the ports of Valparaíso, San Vicente, and Calbuco. The results revealed high non-compliance with the D-2 standard due to high concentrations of plankton in ballast water. A significant diversity of phytoplankton, comprising diatoms and dinoflagellates, was identified and among the zooplanktonic organisms, predominantly marine invertebrates. Physicochemical parameters such as oxygen, temperature, and pH were variable, but within ranges that sustain aerobic life. No pathogens were detected in the microbiological samples, although enterococci and Escherichia coli were found within permissible limits in some vessels. These findings highlight the inefficacy of current ballast water treatments and the need to improve policies and regulations to prevent biological invasions and protect Chile’s marine biodiversity. It is recommended to implement more rigorous and periodical monitoring to strengthen international regulations in ballast water management.

The International Convention for the Control and Management of Ship’s Ballast Water and Sediments plays a crucial role in preserving aquatic ecosystems by aiming to control the introduction of invasive alien species – IAS through ship’s ballast water. By exempting ships operating on specific routes from key regulations (D-1 and D-2), the convention allows for a more flexible approach, considering the risk of IES introduction. Risk assessment plays a fundamental role in this context, as it enables the identification and prioritization of ships with a higher likelihood of introducing invasive species into vulnerable ecosystems. We identified risk scenarios as a way to prioritize ships more likely to introduce IAS and for the potential granting of exemptions to ships discharging ballast water at the port of Santarém, in the Tapajós River, Brazil. Risk assessment (RA) included an analysis of environmental similarity followed by a species-specific analysis. In the first step, we identified the environmental similarity between donor and recipient ballast water ports. In the second step, we quantified the species present in estuarine and maritime ports capable of establishing in the Tapajós River. Ships discharged 3,650,018.6 tonnes of ballast water at the port of Santarém during the analysis period (2014–2019). Among 74 ports of origin, 6 are riverine, 15 estuarine and 53 maritime. Ships from the estuarine ports of Rotterdam, Cabedelo, Aughinish, Montoir, and maritime ports in the Mediterranean and the West Atlantic pose a high risk of introducing IAS into the Tapajós, therefore, they cannot receive exemption and should be prioritised for inspection. This work presents the first RA for the introduction of IAS in an Amazonian port via ballast water and provides information for the development of effective strategies for the prevention and control of biological invasions in the Amazon rivers.

Following establishment, the probability of successful eradication of marine alien species is limited. In the context of kelp forest systems, this is particularly concerning as alien species can lead to dramatic changes in ecosystem structure and even the total loss of kelp. In South Africa, little is known about the status of alien species in kelp forests and there is a need for regular monitoring to support the early detection of incursions and maximise the potential for effective management interventions. However, limited resources dictate that monitoring be done in a cost-efficient manner. Watch lists can support such monitoring. In this study a watch list of alien species with the potential to invade South African kelp forests was developed through a climate-sensitive horizon-scanning approach that accounted for current conditions and predicted climate change. Temperature-matching was used to determine the suitability of the Benguela and Agulhas ecoregions for the watch list species under present and future climatic conditions. The watch list included seven species (the bryozoan Membranipora membranacea, and the algae Bonnemaisonia hamifera, Dasysiphonia japonica, Fucus serratus, Sargassum muticum, Sargassum horneri, and Undaria pinnatifida), some of which have had profound impacts in kelp forest ecosystems in other parts of the world. Overall, kelp forests in the cool temperate Benguela ecoregion appear most vulnerable to invasion, as current and future conditions closely match those under which the watch list species are known to occur elsewhere. This, together with the presence of important ports in the region, highlights the vulnerability of South African west coast kelp forests to invasions and the potential impacts that could result.

In 2019, the South American apple snail Pomacea maculata established a reproductive population in a six-acre retention pond, Bear Lake, in south Austin, Texas, USA. Community-led removal efforts provide a case study to examine how environmental DNA (eDNA) monitoring may play a role in management of biological invasions. Since 2020, concerned neighbors have removed 4,942 snails by hand and destroyed 1,734 egg clutches. In October 2021, we began collecting surface water samples for eDNA analysis with quantitative PCR as visual surveys still occasionally found snails. Without intervention, the high reproductive capacity of P. maculata could cause the population to rebound. However, multiple factors, including homeowner hand removal and cold winter freezes, have kept population numbers low. A few monthly nearshore eDNA samples indicated the ongoing presence of apple snails, and we hypothesized that deeper areas of Bear Lake might provide refuge. To test our hypothesis, we used a Van Dorn sampler to collect water at five mid-lake locations from surface, 1 m, 2 m, and (variable) bottom depths. We detected no eDNA to indicate snail presence in deeper water. Particularly in the colder months (November–January), detection of small amounts of apple snail eDNA in surface water samples occurred without coincident collection of snails or egg clutches, suggesting either a residual source of eDNA or a few individuals remaining. Throughout 2023, we continued to encounter fewer than 5 snails per month, which did not correspond to the monthly eDNA sampling results, indicating standing eDNA concentrations below the limit of detection or a need for more frequent sampling. Overall, due to intense efforts, especially in 2020 (with an estimated 99% of snails removed), visual and eDNA monitoring efforts suggest that the snail population may be close to local extirpation. We recommend cautious optimism but continued vigilance to assure that the population does not recover.

Despite strict regulations, invasive alien species (IAS) pose an increasing threat to native ecosystems. In aquatic environments, difficulties in early detection of invasions make it challenging to control the spread of species such as freshwater crayfish, and hence, effective measures are often needed to eradicate already established populations. We investigated the efficacy of intensive trapping in eradication of signal crayfish (Pacifastacus leniusculus) from a small, isolated lake using a Before-After-Control-Impact (BACI) design with data from three control lakes. Five years of intensive biannual removal of crayfish catch in the target lake resulted in a collapse of the crayfish population, in contrast to increasing test catches in the control lakes. A temporary recovery of the population followed within four years after stopping the removal, but a short-term continuation of the intensive trapping reduced the population to apparent extinction. While small crayfish (< 60 mm in total length) were not effectively caught by the size selective traps, the trial apparently succeeded in limiting the adult crayfish and their reproduction below a critical threshold. Our results support the previous findings that complete direct removal of individuals may not be necessary for successful eradication. Climate-induced reproductive failure and low availability of suitable habitat likely supported our eradication success, highlighting the importance of environmental conditions in invasive species management. Our results emphasise the need for removal projects to be well targeted, long-term, and adequately resourced. Less selective traps catching also small crayfish would need to be developed for enhancing the invasive crayfish species management.

Invasive species, including crayfish, are one of the greatest drivers of change in freshwater ecosystems. The red swamp crayfish (Procambarus clarkii) is an invasive crayfish of particular concern due to the large geographic range where it is established and its ecological effects. Intensive removal efforts can help to reduce invasive crayfish population densities and ecosystem effects, but the most efficient trapping methods vary by study system and target species. We have experimentally investigated trapping methods to design the most efficient program for reducing the population of P. clarkii in a flowing freshwater system. First, we tested the effect of duration that a trap is in the water and found that three nights resulted in the highest Catch per Unit Effort (CPUE; 0.87 crayfish per trap cleared). Second, we tested the catch rates of traps set with different baits and found that hot dogs resulted in the highest CPUE (4.33) compared to four other commonly used bait types (fish, beef liver, dry dog food, and crayfish). Third, we conducted two experiments to test the performance of different trap types. In the first we tested the efficacy of three different trap types and found that nylon mesh traps resulted in the greatest CPUE (2.74) compared to standard traps and tube traps. In the second trap type experiment, we tested the efficacy of standard traps versus two modifications of these traps and found that both modified traps resulted in roughly double the CPUE (standard CPUE 1.13, Mod. 1 CPUE 2.30, Mod. 2 CPUE 2.08). Finally, we determined the distance that P. clarkii travel in our system using a mark and recapture study and found that individuals travel an average of 4.44 m/night. These results can be applied in similar study systems, and/or can serve as a framework for other crayfish removal programs.

The marbled crayfish is an emerging invasive species, mainly due to parthenogenetic reproduction and high adaptability. Its successful eradication seems to be possible only in early detected populations and under favourable conditions. The population of marbled crayfish was discovered in a small urban pond in Prague, Czech Republic, in August 2020. Shortly afterwards, management was initiated with the aim of complete eradication. The pond was harvested and drained twice in November 2020 and October 2021. The crayfish were collected, the exposed pond bottom was treated by liming and left dry over winter. Predatory fish were stocked in the pond after refilling. Survival of the crayfish after the pond draining in 2021 was likely facilitated by up to 40 cm deep burrows found under large boulders. No specimens were observed in the nearby stream and marbled crayfish presence was not detected by environmental DNA screening in the stream and three other standing waters in the vicinity. The combined efforts resulted in a reduction in crayfish densities by an order of magnitude between successive harvests, but complete eradication of marbled crayfish was not achieved by 2023, as individual juveniles were captured during monitoring in the following two years. The perch-dominated fish stock apparently exerts a strong predation pressure that may control the crayfish population, as no marbled crayfish were captured during monitoring in 2024. The current status of the population is unclear, and further monitoring is warranted. Effective cooperation between different institutions and stakeholders has been successfully established, and the public and stakeholders have been educated about the risks of invasive species. However, with prolonged activities aiming to eradicate the crayfish, we also experienced decrease of public support for further radical actions. This experience provides a solid basis for future invasive crayfish management activities at sites with similar conditions.

Pink salmon is an invasive fish species to the North Atlantic Ocean and Barents Sea regions, spreading from intentional releases in north-west Russia. We assess the removal methods used in 94 Norwegian rivers in 2023. In total, 250 000 adult pink salmon were caught when returning from the ocean feeding migration and removed before they were able to spawn. Successful removals show that it is possible to construct bank-to-bank traps to prevent pink salmon from entering even relatively large rivers – despite thousands and even tens of thousands of pink salmon approaching single rivers within a few weeks. Pink salmon by far outnumbered native salmonids, with 11 times more than Atlantic salmon, 35 times more than sea trout, and 13 times more than Arctic char entering the rivers based on trap catches. Traps were used in 50 rivers: resistance board weirs in six rivers, picket weirs in 16 rivers, and wire mesh traps in 28 rivers. Resistance board weirs and picket weirs were easier to keep clean and operate and ensured better fish welfare than wire mesh traps. Timing of river entry of pink salmon and native salmonids overlapped. Native salmonids were sorted out and released alive upstream of the traps. Immediate mortality of native salmonids caught in all three type traps was low (0.1–0.5% of captured fish). Northern Norway is the gateway for spread of pink salmon into the North Atlantic, and future distribution of pink salmon depends on the success of measures in this area. Experiences gained can be used to further develop a comprehensive strategy for removal of pink salmon to improve construction and operation of effective traps with complete coverage in rivers both in Norway and internationally. Improved trap design is also valuable when using large weirs in rivers for other monitoring and management purposes.

Few effective methods for controlling invasive species exist. Within invaded fish assemblages, commercial harvest is a management option. Silver carp (Hypophthalmichthys molitrix) populations are dense throughout much of the Mississippi River basin and are harvested for control and commercial use. Quantifying mortality rates of silver carp and comparing them to other studies will guide expanding removal efforts throughout the watershed. Silver carp total annual mortality was compared between the Illinois River which is heavily harvested and the Wabash River which is not. The contribution of fishing mortality to total mortality should be apparent in the Illinois River if it exceeds natural mortality. Detection and survival probabilities were determined using a longitudinal Cormack-Jolly-Seber model of acoustically tagged adult silver carp during 2011 through 2018 in both rivers, which is a unique approach only possible with long-term data from individual fishes. Proportion detection probability of individuals was consistently > 0.8 among years in both rivers. Survivorship analysis translated to total annual mortality (mean ± 95% confidence interval) for the tagged silver carp in the Wabash River being 0.03 ± 0.02 across all years. This estimate was considerably lower than in the Illinois River where total mortality ranged from 0.23 ± 0.07 in 2017 to 0.78 ± 0.14 in 2014. Despite the high total annual mortality of silver carp in the Illinois River, densities of these fish remain high there, likely due to high reproduction of survivors and immigration from the connected Mississippi River basin. This study serves as a method for evaluating the impacts of large-scale removal efforts. But the relative impact of density-dependent intraspecific feedbacks such as improved reproduction and reduced intraspecific competition of survivors in heavily invaded ecosystems needs to be understood.

Monitoring the occurrence and abundance of aquatic invasive species is a significant challenge for managing freshwater ecosystems, given limited resources. Efficient sampling strategies are essential for early detection and accurate population assessment. Here, we sought to identify the most effective methods and site-selection strategies for sampling an introduced riverine population of Tench (Tinca tinca), a globally invasive fish. A comparative analysis of four fishing methods and deployment conditions revealed fyke nets and gill nets as the most effective gears for capturing numbers of Tench, particularly in areas with a speciose fish assemblage. Gill nets and electrofishing were the most effective for Tench detection. To reduce gear-related mortality of non-target fishes during capture efforts, fyke nets should be prioritized in areas with at-risk species or where high levels of bycatch are expected. Although Tench is considered to be most active at night, time of day had no effect on gear capture effectiveness. The presence of vegetation was slightly correlated with the presence of Tench, while substrate type was not, suggesting habitat preferences in Tench may be more flexible than previously thought. Positive associations between Tench and native fishes across heterogeneous sites corroborate a preference by Tench for low-flow, vegetated areas. These associations have the potential to inform site selection for sampling at the invasion front. Our study revealed gaps in knowledge of the ecological relationships between Tench and environmental variables associated with its capture. Nonetheless, our results point to methods for maximizing Tench detection and capture efficiency and for targeting habitats or sites where the species is likely to occur. This information is necessary for informing mitigation plans in established areas and supporting early detection and removal of Tench along the invasion front, with the ultimate goals of slowing its secondary spread.

Practitioners of community science who are based at a locality and who are familiar with the local ecosystem can provide opportunities to supplement formal monitoring efforts. Between 2021 and 2023, we established a working relationship with a year-round resident recreational fisher who was engaged with monitoring as a community scientist. As a result, the first extralimital record of Portunus segnis (commonly known as the blue swimming crab) in temperate waters of South Africa was detected in January of 2020 in the Kowie River on the south coast. Following this discovery, two additional specimens were found in the estuarine reaches of the same river in December 2021. This report provides evidence of a population of P. segnis persisting outside its native tropical range and, in addition to morphological identification, species verification was confirmed using genetic barcoding. The circumstances of finding these specimens underscore the importance of establishing and maintaining relationships between local resource users and researchers to facilitate the identification and monitoring of introduced and range expanding species and to provide formal scientific documentation and rapid communication of species occurrences and persistence outside their native range.

Invasive terrestrial plant, Furcraea foetida (Mauritius hemp) originates from central and South America and is invasive in South Africa. The species predominantly reproduces asexually by producing copious bulbils that facilitate spread (especially down slopes). In this study, we investigated the efficacy of a herbicide (viz. fluroxypyr/picloram), both in situ and ex situ, to control bulbils of F. foetida. Additionally, given the increasing evidence that suggests that climate change could alter the growth and physiology of invasive alien plant species, and hence their management, we also investigated bulbil responses to reduced water availability. For the in situ herbicide investigation, three study sites were selected along the coast of KwaZulu-Natal (South Africa) and seventy herbicide-treated and seventy untreated bulbils (per site) were monitored. There was 0–13% bulbil survival in herbicide-treated bulbils compared to 100% survival in control bulbils in situ after four weeks. In bulbils that survived, the herbicide appeared to limit rooting, which might also limit recruitment. For the ex situ experiment, we planted herbicide-treated bulbils, that were subjected to different durations of herbicide exposure, in a shade house and found that all herbicide-treated bulbils died after 28 days. The irrigation experiment showed no negative physiological effects on root length, plant height, chlorophyll content and leaf area in bulbils subjected to a water deficit. However, it should be noted that the final biomass was significantly higher in water-deficit treated plants (2.83 g) compared to the normally irrigated plants (0.82 g) indicating that the species may be adapted to arid climates. This study found that [2.5%] fluroxypyr/picloram is effective against F. foetida bulbils, suggesting that chemical control by targeting the bulbils is a potential management option to minimise spread and invasiveness. The study also suggests that F. foetida has the potential to tolerate drought conditions in subtropical KwaZulu-Natal, which advocates for the prioritisation of managing populations in arid regions of South Africa. .

Small hive beetles (Aethina tumida, Coleoptera: Nitidulidae; SHB) are invasive parasites of bee nests that have spread to all habitable continents since 1996, causing significant damage to apiculture. This paper documents a decade of successful SHB eradication and containment applied in some regions of southern Italy. After the first detection of SHB in Italy in September 2014 in Gioia Tauro, Calabria region, and subsequent detection in Sicily in November 2014, intensive surveillance and eradication efforts were promptly initiated. These measures, including the destruction of infested apiaries, the establishment of protection and surveillance zones, and continuous monitoring through sentinel nuclei, have effectively contained the spread of SHB. No further SHB outbreaks have been detected in Sicily since 2019, and the pest remains confined to a limited area in Calabria region. The successful containment and eradication in Italy emphasize the importance of early detection, prompt action, and continuous adjustment of measures in response to the evolving epidemiological situation. The data suggest that the flight of adult SHBs and the use of hosts other than managed honeybees play a minor role in the spread of the beetle. This case represents an effective model for management of this invasive species, highlighting the critical roles of stakeholder engagement, regulatory support, and financial compensation for affected beekeepers. .

Documentation of successful early detection rapid response (EDRR) efforts is lacking from the scientific literature but is needed to inform invasive species response protocols. The Black and White Tegu (Salvator merianae) has become established in several Florida counties and its spread is of significant conservation concern. It is a high priority for State and Federal managers to prevent tegu spread into sensitive ecosystems, including the Greater Everglades. Thus, coordinated EDRR efforts are essential given limited infrastructure and funding for such tasks. While tegus have known populations east and west of Big Cypress National Preserve, there is no evidence to indicate tegus are established within the preserve. On 8 August 2024 a tegu was sighted by a U.S. Geological Survey (USGS) biologist in Big Cypress National Preserve, who alerted National Park Service (NPS) staff and mobilized a response. Within 24 hours, live traps were placed at the location of sighting and a tegu was captured on 13 August 2024. The tegu was determined to be the same individual that was observed five days earlier based on color, pattern, and other physical characteristics. No additional tegus were captured in the 48 hours that traps were left open following capture of the target individual. The rapid, coordinated response of NPS and USGS certainly contributed to this successful EDRR event, and highlights the need for more expansive EDRR frameworks at multiple jurisdictional scales. .