Hundreds of fish species enter the United States through human intervention (e.g., importation) and some of these fishes pose a substantial risk to the nation’s assets and ecosystems. Prevention, early detection, and rapid response (EDRR) are vital to stop species invasions, but time and resources to manage the large suite of fish species that enter the nation are limited. Evaluating the risk of a species’ invasion in a location is one way to prioritize among many species for management action. Species risk assessments are often associated with information systems or are published within grey literature or peer-reviewed journal articles. Improving access to available risk assessments could help in prioritizing management action for the most potentially invasive fish species. We aggregated fish species risk assessments, synthesizing the current knowledge on the risk of fish invasions in the United States. To accomplish this, we searched information systems and conducted a literature review. We then summarized risk assessment results along with the importation statuses of fish species and identified if imported, high-risk species are managed under federal or state policy. Within the scope of the conterminous U.S., we found 98 high-risk fish species. Eighteen of these species are imported to the country, but only three species have been recently prohibited from importation according to the Lacey Act. We observed similar patterns at the scales of the Great Lakes region and Florida. Collectively, our work provides a baseline estimate of the high-risk fish invaders that enter the U.S. through importation, underscoring species to consider for priority management action, as well as a benchmark of species that lack risk assessments. Insights from this work can be enriched when joined with other invasive species information, which could be accomplished through a national EDRR information system, an information sharing hub in development by the U.S. Geological Survey.

We conducted a review to summarize the settings, configurations, and capture data for an array of fisheries gear types used to capture invasive bigheaded carps (Hypophthalmichthys spp.) in North America. The goal of this paper was to synthesize patterns of bigheaded carp catch data across various gear types and capture methods. Data consisted of bigheaded carps captured among a variety of riverine habitats where their populations are well-established (e.g., lower pools of the Illinois River), as well as near the leading edge of their invasion front (e.g., Upper Mississippi, Upper Illinois, Upper Missouri, Red River). Our synthesis provides a summary of (1) capture gears and their settings/configurations, (2) catches (fish size, number captured, precision of estimates), and (3) assessment of gears that were robust (i.e., high precision, low cost, high catch, sample many habitat types) in riverine environments and impoundments. Across the 26 gear types used to target bigheaded carps, catch rates of silver carp were consistently higher than bighead carp, which may result from a combination of sampling inefficiencies, sampling biases, and spatial dynamics of their invasions. Gear performance matrices combining catch rate, precision, and labor cost indicated that DC electrofishing and herding fish into gill nets and/or trammel nets were the top-ranked capture methods. This review provides guidance for the development of detection, monitoring, and control programs that target bigheaded carp species, as well as identifies future research to fill critical data gaps.

Invasive Non-Native Species (INNS) are a principal threat to global biodiversity and the early detection of new introductions is key to facilitate a rapid response to limit the risk of establishment and spread. Related to this, there is growing interest in using environmental DNA (eDNA) for INNS detection. The applied use of eDNA in ecology is, however, in its relative infancy with few species for which regulator-approved methods are available. Here, laboratory trials were conducted to investigate the use of commercially available eDNA assays for detecting two high priority INNS in the UK, killer shrimp (Dikerogammarus villosus) and signal crayfish (Pacifastacus leniusculus), at different population densities. For killer shrimp, DNA of the expected fragment size was detected from all three trials where animals were maintained at a density of 1 per 1 L but species confirmation by Sanger sequencing was only possible for one of these replicates. Whilst capillary electrophoresis detected DNA of the expected fragment size in serially diluted samples down to a density of 1 shrimp in 100 L, this could not be confirmed by sequencing. Signal crayfish DNA was detected by qPCR in all four trials where animals were housed at a density of 1 per 10 L. Using serial dilutions, it was possible to detect signal crayfish in samples representing a density of 1 per 1,000 L, however this was unreliable. These results demonstrate the potential for using eDNA as a detection method for killer shrimp and signal crayfish but also highlights that detectability is species/assay specific and dependant on population density. The insights gained will help inform decisions surrounding the appropriateness of using these eDNA assays, and improve interpretation of any results generated.

Grass carp (Ctenopharyngodon idella), an invasive cyprinid within the Laurentian Great Lakes, is naturally reproducing in several Lake Erie tributaries, which has raised concerns of the species’ spread throughout Lake Erie and the other Great Lakes. Knowledge of the recent invasion extent outside of the western basin of Lake Erie, particularly in eastern tributaries and nearshore waters, is limited. Understanding the invasion extent would improve the efficacy of ongoing coordinated multi-agency control efforts. Molecular tools, such as environmental DNA (eDNA), have shown promise for early detection of aquatic invasive species. In this study, water samples (N = 476) were collected for grass carp eDNA monthly between May and November in 2018 and 2019, at three sites in the Michigan waters of Lake Erie and the Detroit River. We fit Bayesian multi-scale occupancy models to determine differences in eDNA capture and detection probability among grass carp qPCR assays, sampling sites, and across time. To determine whether grass carp were physically present, and to validate eDNA samples, we quantified recent grass carp presence in sampled areas using an existing acoustic telemetry and field sampling framework. Our results indicate that grass carp eDNA capture probability differed among sites, but there was no difference among months. Positive grass carp eDNA detections were observed across multiple months at each site, with 69% of site-specific sampling events testing positive for grass carp eDNA on at least one assay and replicate. The majority (65%) of weeks where positive eDNA sampling detections occurred also concurrently had one or more grass carp detected via acoustic telemetry 1–6 days prior. Our results highlight the potential utility of using eDNA to monitor the invasion extent of grass carp within the nearshore waters of Lake Erie. However, further evaluation of the factors that influence grass carp eDNA characteristics among sites within Lake Erie are needed to determine its efficacy for surveillance protocols by natural resource management agencies.

Invasive non-native freshwater fishes have long been recognized as a threat to biodiversity conservation and management. Non-native fishes with a high risk of becoming invasive can be identified using risk screening tools. Here, we used the Aquatic Species Invasiveness Screening Kit (AS-ISK) to identify the invasion risk of non-native fishes in Yunnan Province, China. AS-ISK scores were calibrated to distinguish between species with high and low-to-medium risks of invasiveness. Risk threshold was 17.25 for BRA (Basic Risk Assessment) and BRA+CCA (BRA+ Climate Change Assessment) in Yunnan Province. Based on BRA scores, 21 of the 37 screened species were classified as high risk, 13 as medium risk and 3 as low risk. Based on BRA+CCA scores, 22 of the 37 screened species were classified as high risk, 12 as medium risk and 3 as low risk. For both BRA and BRA+CCA, the highest-scoring species were Hypostomus plecostomus, Oreochromis aureus, Oreochromis mossambicus and Oreochromis niloticus. This study reliably assessed the risk of non-native fish invasion in Yunnan Province and identified priority non-native fishes for prevention and control, providing information for targeted monitoring and management decisions in the region.

As invasive zebra mussels (Dreissena polymorpha) continue to spread through the freshwaters of the United States, efforts have been made to develop mussel invasion risk assessments to focus invasion prevention, monitoring, rapid response, and macrofouling control on at-risk water bodies. Previous invasion risk assessments have been based on broadly applied single factors such as calcium concentration or summer water temperature or on global scale climate variables. While such factors applied on a nationwide basis provide a general overview of regions susceptible to mussel invasion, they do not determine mussel invasion risk for specific water bodies, which can be variable even among those that are closely adjacent. Furthermore, these broad risk assessments may over or underestimate risk due to lack of water body specificity. In order to develop effective mussel prevention and control strategies, managers need mussel invasion risk assessments that can be applied to specific water bodies allowing limited resources to be focused on those most likely to be invaded. This study reports the use of easily determined factors (i.e., calcium concentration, pH, salinity, and summer surface water temperature) to specifically determine mussel invasion risk for 133 Texas water bodies as a case study of simplistic methods with broad geographic applicability. The results indicated that 19.5% of the water bodies had a minimal invasion risk, 9.8% a moderate risk, and 70.7% a high risk. This study demonstrates that these methods provide finer scale risk assessment for Texas water bodies in this case study, finding higher risk in western and southern regions than was predicted by climate-based risk assessments and more nuanced risk levels in the eastern region than predictions based on calcium alone. These methods can provide invaluable information for natural resource managers and water infrastructure operators on a broad geographic scale to guide monitoring and mitigation efforts.

Dreissenid mussels (quagga and zebra mussels, Dreissena bugensis and polymorpha) continue to spread throughout inland waterbodies of North America. Although there are considerable management and mitigation efforts underway to prevent infestation of new waterbodies, there have been relatively few successful efforts to eradicate mussels once detected due to a lack of cost-effective treatments. Two potentially cost-effective molluscicidal agents, potassium chloride (KCl, also called muriate of potash) and copper (formulated as Earthtec QZ®), have successfully treated infested waters, but have varying efficacy under different water quality and temperature conditions, and to date have only been applied in moderate conductivity waters (defined here as < 400 µS/cm) common throughout North America. Natural resource managers need information on the efficacy of these chemicals in high conductivity waters more typical of riverine systems and arid climates, in addition to the range of water temperatures typically encountered in the field. We evaluated the dose-response of quagga mussels to KCl and Earthtec QZ® in high conductivity water (≈ 700–1,400 µS/cm) across a range of temperatures (10, 18, 22 °C) to determine appropriate doses and treatment duration resulting in 100% mortality. Our data indicate that treatments in cool temperatures (i.e., 10 °C) may be challenging for eradication efforts in high conductivity waters because none of the KCl treatments and only one copper treatment resulted in 100% mortality within the experimental period. However, both KCl (> 200 ppm) and copper (120 and 180 ppb) were consistently able to induce 100% mortality in quagga mussels in warmer temperatures (i.e., ≥ 18 °C) and thus may be good candidates for field scale application in high conductivity waters. The results of this study indicate that field-scale application should strongly consider environmental conditions during the period of application when selecting dosages and treatment duration.

Invasive marine species (IMS) are a major anthropogenic threat to global marine environments. To mitigate the threat, Australian federal and state governments have developed detailed quarantine programs to minimise IMS introductions, supported by monitoring programs to detect any IMS that penetrated the quarantine barriers. Considerable shipping movements occur between the Pilbara region of northwestern Australia and southeast Asia where a number of potential IMS oysters occur. eDNA techniques are being developed to rapidly scan biofouling and other samples for potential IMS, but there is limited information on oysters present in the Pilbara. We collected intertidal oysters in and near Pilbara ports and identified them using DNA sequences to determine if any IMS are present and to provide a baseline to prevent false positive results for IMS by native species. Only three species were detected: native Saccostrea lineage A and S. scyphophilla, both widespread in the Pilbara, and Talonostrea sp. nov. which had not previously been reported from the Pilbara. No IMS oysters were found. The study provides a solid basis for monitoring for any future occurrences of IMS oyster species in the Pilbara, an area with a very high known shallow water marine biodiversity, but where only a single IMS is known to occur.

Four native chelonians species occur in Spain, three of which are severely threatened. In recent surveys, 25 species of alien turtles and tortoises were reported, some of which had established breeding populations and interfered with native species. In this study, we used ecological niche models to evaluate which regions are more vulnerable to colonization by alien turtles and tortoises and which alien chelonians show substantial environmental overlap with native species. The parameters of the ecological niche models were iteratively optimized using Akaike procedures, and we assessed the projection transferability between donor and recipient geographic regions using Mobility-Oriented Parity estimation. Our results indicated that the Mediterranean and some Atlantic rivers (Miño-Sil and Guadalquivir) are particularly vulnerable to colonization by semi-aquatic alien turtles, while southwestern Spain is exposed to colonization by alien tortoises. The aquatic species most susceptible to overlap with the four species of native turtles are those native to the cold and warm temperate regions of North America and China: Apalone spinifera, Chelydra serpentina, Chrysemys picta, Mauremys mutica, Mauremys reevesii, Mauremys sinensis, Pelodiscus sinensis, Sternotherus odoratus, and Trachemys scripta. These results highlight the importance of establishing stricter trade regulations for certain species with a focus on protecting vulnerable areas.

Early detection and rapid response (EDRR) can minimize the impacts of invasive species, which cost billions of dollars globally. To bolster EDRR across the United States, the U.S. Department of the Interior is working with the U.S. Geological Survey and other partners to advance a National EDRR Framework that strengthens tools, actions, and processes to find and eradicate invasive species before they establish and cause negative impacts. An important component of this framework is to strengthen molecular tools for detecting new invasions. The Rapid Environmental (e)DNA Assessment and Deployment Initiative & Network (READI-Net) project is developing automated eDNA sampling tools and processes to ensure that eDNA results are reliable for management decision-making, and information structures to deliver eDNA results to end-users. To improve the potential uptake of this molecular EDRR toolbox, READI-Net investigators met with a group of end-users, partners, developers, and subject-matter experts from federal agencies, tribes, universities, and an NGO representing state agencies from February 28 to March 1, 2023, in Moss Landing, CA. Here, we summarize the READI-Net project and the corresponding participant feedback.