The rapid growth of marine trade and associated activities has led to an ever-increasing number of non-native species (NNS) being transported around the globe. Once established, NNS can be further spread by human activities. The spread of NNS is a trans-boundary challenge that must be met through a range of management measures operating over international and local scales. In contrast, the responsibility of managing NNS post-introduction often fall on marine managers working within localised areas of jurisdiction, such as ports and marinas. Here we examine how legislative frameworks, risk management and perception, influence the ability to develop and implement biosecurity planning in an offshore, semi-autonomous island community; the Shetland Islands. We propose a holistic approach to biosecurity management by integrating risk management methodologies into the wider management process of marine spatial planning. The challenges and opportunities created by a bottom-up approach to management are assessed within the context of global, pan-European, national and local management measures (e.g. regulations, treaties and policies). This paper sets out a framework for managing risk in an environment where the actions of many actors are outside the direct control of those tasked with managing the ecological and socio-economic impacts of marine NNS.

The pragmatic management of invasive alien species should integrate two essential items: 1) management interventions and 2) a spatially explicit management plan. Predicting the future expansion of target species in a region at the early invasion stage is an important step toward the establishment of a spatially explicit management plan. However, information regarding the distributions of target species is limited, making it challenging to predict range expansions. In the present study, we established a simulation model that could predict the future expansion of the invasive insect Aromia bungii, which is harmful to Prunus trees (including cherry trees [Cerasus × yedoensis]), in Japan. We employed a virtual ecology approach that simulated species dynamics based on a simple model in Saitama Prefecture, which is in the Kanto region of Japan. Since the first record of the species in this region of Japan in 2013, its range has expanded dramatically. Three candidate pathways and combinations of these for the range expansion of A. bungii were tested to identify the major proxies of expansion for this species, followed by the validation of these results using occurrence records for the species through 2019. Both the river density model and combined river and road density models showed good predictive performance. Using these models, we established a predictive map of the future expansion of this species in the wider range of the simulation area. Based on the results, we recommend concentration of management efforts in the mid-northeast region of the Saitama Prefecture.

At least 65 aquatic plant species have been identified as part of a surveillance list of non-native species that pose a threat to biodiversity and ecosystem services in the Laurentian Great Lakes. Early detection of these potentially invasive aquatic plants (IAP) could minimize impacts of novel incursions and facilitate successful eradication. We developed, implemented, and then adaptively refined a probabilistic boat-based sampling design that aimed to maximize the likelihood of detecting novel IAP incursions in large (400+ hectares) Great Lakes coastal areas. Surveys were conducted from 2017 to 2019 at five Great Lakes locations – St Joseph River (MI), Saginaw River (MI), Milwaukee (WI), Cleveland (OH), and the Detroit River (MI). Aquatic plant communities were characterized across the five sites, with a total of 61 aquatic plant species detected. One-fifth of the species detected in our surveys were non-native to the Great Lakes basin. Sample-based species rarefaction curves, constructed from detection data from all surveys combined at each location, show that the estimated sample effort required for high confidence (> 95%) detection of all aquatic plants at a site, including potentially invasive species, varies (< 100 sample units for Detroit River; > 300 sample units for Milwaukee, roughly equivalent to 6 to 18 days sampling effort, respectively). At least 70% of the estimated species pool was detected at each site during initial 3-day surveys. Leveraging information on detection patterns from initial surveys, including depth and species richness strata, improved survey efficiency and completeness at some sites, with detection of at least 80% of the estimated species pool during subsequent surveys. Based on a forest-based classification and regression method, a combination of just five variables explained 70% or more of the variation in observed richness at all sites (depth, fetch, percent littoral, distance to boat ramps and distance to marinas). We discuss how the model outcomes can be used to inform survey design for other Great Lakes coastal areas. The survey design we describe provides a useful template that could be adaptively improved for early detection of IAP in the Great Lakes.

Global ballast water management aims to reduce the transport and introduction of non-indigenous species through practices such as ballast water exchange and ballast water treatment. Comprehensive enforcement to ensure vessels are meeting ballast water management requirements are a key part of success, but such activities are limited by available resources. Targeted and/or stratified enforcement activities are one option to make best use of available resources. International vessels are required to submit ballast water reporting forms prior to arrival at many ports around the world, declaring quantities, geographic sources, management undertaken and expected discharge location. These data are essential for risk assessment and trends analysis, but the inflow of data can be overwhelming for daily operations, particularly for jurisdictions with many ports and/or high vessel traffic. Having near real-time access to ballast water data enhances opportunities for data validation and verification and facilitates customized reports such as mapping of exchange coordinates and ballast water discharge statistics. Customized software enables seamless application of best-available science through integration of decision-support tools. The Ballast Water Information System (BWIS) was developed to support daily ballast water enforcement activities and scientific research in Canada. The BWIS increases accessibility of ballast water report data and streamlines data processing to support decision-making using an on-line platform.

Worldwide over 910 terrestrial planarian species have been described. They mainly occur in tropical and subtropical regions. In Europe, 22 alien terrestrial planarian species have been recorded over the last decades. In The Netherlands, 9 alien species have been found so far, mostly in greenhouses. Three of these species have established populations in gardens (i.e., Marionfyfea adventor, Caenoplana variegata and Parakontikia ventrolineata). Alien terrestrial planarians that consume earthworms and are established outdoors can have a negative impact on biodiversity and soil quality by reducing earthworm populations. Their impact on earthworm populations can be high, but is difficult to assess due to limited knowledge of the feeding patterns and ferocity of most terrestrial planarian species. Risk assessments for The Netherlands carried out with the Harmonia+ scheme shows that only the New Zeeland land planarian Arthurdendyus triangulatus scores high for potentially risks due to its ability to significantly reduce earthworm densities. This species has not yet been found in The Netherlands, but already occurs in the United Kingdom, Ireland, and Iceland. Obama nungara obtained a medium risk score and all other species a low risk score. Due to the limited information about terrestrial planarians and their potential impact, the certainty of most risk scores is low to moderate. Therefore, it is recommended to update their risk assessments periodically based on new information about their invasion biology. Phytosanitary measures can limit the unintentional import of alien planarian species.

The eradication of the aquatic invasive Australian swamp stonecrop Crassula helmsii in North-western Europe usually fails. This is especially true for areas where this plant species is abundant and wide spread or the probability of re-infestation is high due to hydrological connectivity with other infested surface waters or wetlands. Therefore, the large-scale eradication of this invader is often assumed not to be cost-effective. In 2018, C. helmsii was eradicated in a wetland of 4.5 ha covering interconnected humid dune valleys on the Wadden Island of Terschelling in the Netherlands. The total costs of this large-scale project were estimated to be 1.5 million euro. The applied method was excavation of infested locations and replenishing these areas with clean (uncontaminated by C. helmsii) sand to restore boundary conditions suitable for recovery of the treated habitats in this Natura 2000 site. An eight step approach was implemented to eradicate the invasive plant species. Aftercare consisted of a monitoring program with six-weekly vegetation surveys for early detection of any regrowth of C. helmsii and assessment of the effectiveness of the eradication measures. The eradication of C. helmsii was regarded successful since this fast growing plant species was not observed in the areas of concern during a period of at least two years. The results of a strength, weaknesses, opportunities and threads (SWOT) analysis revealed that the method for eradication of this invasive plant species was effective to secure nature values but also complex, time consuming and costly. Our lessons learnt and recommendations for management will help other nature managers making the right decisions in determining appropriate eradication measures for C. helmsii.

A benthic geotextile was used to trial the management of an invasive aquatic macrophyte Nuttall’s pondweed (Elodea nuttallii (Planch.) H. St. John, 1920) in Lough Arrow, a premier trout angling lake in the north-west of Ireland, designated as a Natura 2000 site (Special Area of Conservation (Annex I habitat, “Hard oligo-mesotrophic waters with benthic vegetation of Chara spp.”) and Special Protection Area for birdlife). The aim of this study was to manage E. nuttallii, a relatively recent arrival to this lake, while simultaneously promoting rehabilitation of native charophytes. The trial was carried out in Loughbrickbay, one of the lough’s primary boating launch sites, an area determined as highly infested with E. nuttallii. Two experimental areas covering a total of 800 m² were treated by covering the invasive weed and substrate with jute textile, a single and double layer respectively. The trial was successful in controlling E. nuttallii for both single (P = 0) and double layer treatments (P = 0.002). The treatments applied resulted in a reduction of the mean percentage cover of the invasive species by > 60% for both treatments. Post-treatment mean percentage cover of E. nuttallii did not exceed 6% for either treatment. Furthermore, the mean percentage cover of indigenous charophyte flora present pre-treatment was not significantly impacted by the application of jute in either the single (P = 0.165) or double treatment (P = 0.353). For biosecurity purposes, the treatment areas were strategically positioned in close proximity to the bays pier and slipway. The treated transects were marked with navigational buoys to provide a corridor for boats entering and exiting the lake, which help to contain the invasive within the Natura 2000 site while reducing the spread risk via this pathway to other sites vulnerable to infestation.

The coastal dune at the natural protected area of Cozumel Island has been impacted by the invasive Australian pine (Casuarina equisetifolia), which is highly competitive with the native species and only few native plant species can grow under its canopy. Our goal was to demonstrate that the Australian pine’s presence reduces the cover and vegetation diversity of the coastal dune’s native species. We used ten sampling plots (100 m² each), five of which included Australian pine (invaded), and five that did not (non-invaded). We recorded the number of different plant species and their cover, height, and diameter in each plot. We found 43 plant species belonging to 40 genera, from which 37 species were found in the non-invaded plots, while only 26 plant species were present in the invaded ones. The vegetation density (3547 ± 709 individuals ha^-1) and the cover (65%) in the plots that lacked Australian pine were higher compared to the density (2785 ± 802 individuals ha^-1) and cover (35%) of the plots that included it. According to our analyses, Australian pine presence negatively influenced the species composition and abundance of the native species. Moreover, we found significant differences in the native plant diversity between the invaded and non-invaded plots. Our results demonstrated that invasive species, such as the Australian pine, negatively affected the native plant community in the coastal dune because it constrained its community structure.

Invasive, plague-carrying signal crayfish represent a significant threat to imperiled European crayfishes. In the absence of a feasible eradication technique, physical barriers that separate invasive from native crayfish populations have been suggested as management strategy. Here, we investigated the effectiveness of three serial barriers with different functionality (flow-based vs. waterfall-based) in a headwater stream in southwestern Germany on containment of signal crayfish and crayfish plague. Crayfish distribution was surveyed three and six years after the construction of the barriers using manual search, trapping, and eDNA detection, whereby a tributary stream without barriers served as a form of control for a “do-nothing” scenario. The efficacy of the barriers was also empirically assessed by stocking marked crayfish downstream of the barriers and tracking their nocturnal behavior. After six years, native crayfish were still present upstream of the barriers but went extinct in the control stream due to signal crayfish invasion. Following two years of extreme drought after the first survey, signal crayfish were able to overcome the flow-based barrier but were never detected upstream of the waterfall-based barriers. Overall, this case study provides evidence for the effectiveness of intentional stream fragmentation as management strategy against invasive aquatic species.

The spread of aquatic invasive species typically occurs through a combination of natural and human mediated dispersal. For many aquatic invasive species, natural dispersal is limited to aquatic corridors connecting habitat. In contrast, human transport may facilitate more distant dispersal and transport among disconnected waterbodies. Genetic information can serve as a powerful tool to track invasion histories and identify both the sources and mechanisms of invasive species dispersal. We used genetic information to understand invasion history and dynamics of expanding northern pike invasion in the Columbia River basin. Results indicate that the initial introduction of northern pike into the Pend Oreille River (in eastern Washington State) resulted from human transport of fish, not dispersal from established populations upstream. Subsequent reproduction and natural dispersal from the Pend Oreille River resulted in downstream expansion of northern pike into Lake Roosevelt, a reservoir within the mainstem Columbia River. These results highlight the need for a holistic approach to suppression of invasive species. Immediate efforts must address the biological mechanisms of natural dispersal. Sustained suppression and eradication must take a broad approach that includes coordination between management agencies, as well as policy and public outreach aimed at prevention of repeated human transport events. The genetic database created from this study has already been used to eliminate potential source populations for new northern pike invasions in Washington State outside the Columbia River basin. This highlights the utility of genetic monitoring for both immediate and long-term applications to managing aquatic species invasions.

Aquatic invasive species (AIS) are a major threat to aquatic ecosystems worldwide. Despite management efforts, human assisted dispersal continues to distribute AIS within and across waterbodies. An understudied translocation vector for AIS, especially for invasive fish, are the cooling systems of small watercraft motors. Here, we investigate the contents of boat motor cooling systems for the presence of invasive goby larvae in a collaboration with local boat owners. Because of the exclusively nocturnal drift activity of goby larvae, to collect samples we drove boats in the first hours after sunset. For an estimate of the translocation potential, we quantified drift density of goby larvae as well as boat traffic after sunset. We found a goby larva in a boat motor once in 30 boat drives of 1–2 hours duration each. Peak drift densities of goby larvae were 2.5 per 100 m³, which is comparable to previously reported data. Recreational boats were active after sunset throughout the reproductive season of invasive gobies and are therefore a realistic translocation vector for goby larvae. Additionally, evidence of fish and other animals inside boat motor cooling systems, gathered from online boating forums, demonstrates the potential of AIS transport in small watercraft. Translocation inside motors is especially likely for in-water transport of boats, which should be a management focus in interconnected aquatic systems.

Non-physical deterrence and guidance technologies are sought after for management of invasive fish, but they have rarely been tested in the field during natural fish migrations. We tested the efficacy of a semi-portable deterrence and guidance system (DGS) that used vertical electrodes producing low-voltage electric field to deter the upstream spawning migration of common carp (Cyprinus carpio Linnaeus, 1758) and direct them into a trap (5 m by 25 m enclosure with a net) in a natural stream. The behavior of carp was monitored using Passive Integrated Transponder (PIT) tags and antennas. The migration began on 7 April 2019, when water temperature was 5 °C and lasted through May 2019. Performance of the DGS was evaluated during three separate periods, between which the DGS was briefly deactivated. During the first period (4/7–4/19), 559 unique carp challenged the DGS. Of those, 10 were able to cross the DGS (98.2% efficacy), 234 (41.8%) were directed into the trap and 54 were captured. The mean number of days each carp was detected at the DGS was 2.6. During the second period (4/25–5/7), 562 unique PIT carp challenged the DGS. Of those, 24 were able to cross it (95.8% efficacy), 241 (42.9%) were directed into the trap and 148 were captured. Mean time at the DGS was 5.6 days. During the third period (5/7–5/15), 147 PIT carp challenged the DGS and 2 were able to cross it (98.6% efficiency). The mean time at the DGS was 5.5 days. Due to decreasing numbers of carp during the third period, we did not attempt to direct them into the trap for removal. Stream discharge during our test exceeded the 11-year average by 2–3 times; the floodplain was periodically flooded, and it is possible that some carp migrated around the DGS rather than through it. Overall, our results suggest that DGS that generate mild, electric field can be useful in deterring seasonal migrations of common carp and facilitating new removal strategies. The semi-portable nature of the system and low site-engineering requirements allow for rapid deployments and targeted applications during seasonal migrations.

There is an urgent need to block the passage of carp and other invasive fishes through navigational locks in large rivers. Although the broadband sound of an outboard motor has been shown to strongly repel three species of carp in laboratory flumes and to a lesser extent inside of a lock chamber, it has not yet been tested to see if it can stop carp from entering a lock. To test this possibility, we attached speakers to lock gates and played the sound of an outboard motor while measuring its efficacy by tracking free-ranging transplanted tagged common carp in its vicinity. Eight groups of 20 carp were tested while the sound system was turned on and off for 2 week periods. When the sound system was on, these carp spent approximately one-third less time in front of the lock gates than when it was off; however, when analyzed by a GLMM this effect was shown to be no greater than the effects of river discharge or temperature. Additionally, lock entrance rates were lower, albeit non-significantly, when the sound was off. A number of factors may have contributed to the limited efficacy of this deterrent system including the sound itself.

Roach (Rutilus rutilus) is indigenous to south-eastern Norway and alien to the rest of the country. In Trondheim municipality, in the middle part of Norway, roach was introduced into the Ila watercourse in 1881. Roach has a great potential to alter the ecosystem when introduced to new locations. The potential negative impact on potable water source quality and the prospect of permanently eradicating an alien species resulted in rotenone treatment of six lakes in Trondheim municipality. The rotenone concentration in the lakes was surveyed by water sampling until it could no longer be detected. A lethal concentration of rotenone at all test points was measured in all lakes during the survey period. Fourteen days after treatment, a near homogenous concentration was reached. The concentration reduction was similar in the lakes and relatively quicker during the first weeks after treatment. It was also consistent between depths except for the surface, where the concentration degraded more quickly. Rotenone degradation is a key factor when planning eradication efforts, and reports on this varies considerably between different locations. Despite application of rotenone in different depth strata, it took several days to reach homogenous concentration and several months and a fall turnover for the rotenone to break down and dilute below the detection limit in the lakes described.

The Chinese bullfrog, Hoplobatrachus rugulosus (Wiegmann, 1834), naturally distributed in Thailand, Laos, Vietnam and China, is commonly used in the religious practice of mercy release. The release of H. rugulosus is complicated by the fact that it likely represents a cryptic species complex (multiple species under a single name). In Hong Kong, although there are native and released individuals, the impact of release has not been investigated. In this study, we conduct genetic and morphological analyses of H. rugulosus across Hong Kong to determine the source (native or released) of frogs, the distribution of released populations and identify morphological characteristics that can be used to differentiate native and released individuals. We found that H. rugulosus individuals in Hong Kong belong to the two major genetic clades identified in previous studies (Clade A and Clade B). We consider individuals in Clade A as released frogs based on the genetic result that cluster these individuals with wild H. rugulosus from western, central and eastern Thailand, and individuals from Chinese frog farms. Individuals from the two genetic clades differ based on morphology (dorsal color, coloration of loreal region, presence of wounds and coloration on lateral sides), that can be useful for identification. However, there are four individuals in Clade A that are morphologically similar to native frogs, raising the possibility of hybridization between individuals in the two clades. We strongly recommend that the mercy release of H. rugulosus and other exotic animals should be strictly prohibited by law in Hong Kong and other parts of the world. Eradication guidelines should be developed by experts, as a references for governments, conservation groups and the public.