Non-native Crayfish Research Articles

World of Crayfish™: a web platform towards real-time global mapping of freshwater crayfish and their pathogens

Freshwater crayfish are amongst the largest macroinvertebrates and play a keystone role in the ecosystems they occupy. Understanding the global distribution of these animals is often hindered due to a paucity of distributional data. Additionally, non-native crayfish introductions are becoming more frequent, which can cause severe environmental and economic impacts. Management decisions related to crayfish and their habitats require accurate, up-to-date distribution data and mapping tools. Such data are currently patchily distributed with limited accessibility and are rarely up-to-date. To address these challenges, we developed a versatile e-portal to host distributional data of freshwater crayfish and their pathogens (using Aphanomyces astaci, the causative agent of the crayfish plague, as the most prominent example). Populated with expert data and operating in near real-time, World of Crayfish™ is a living, publicly available database providing worldwide distributional data sourced by experts in the field. The database offers open access to the data through specialized standard geospatial services (Web Map Service, Web Feature Service) enabling users to view, embed, and download customizable outputs for various applications. The platform is designed to support technical enhancements in the future, with the potential to eventually incorporate various additional features. This tool serves as a step forward towards a modern era of conservation planning and management of freshwater biodiversity.

Global invasion and biosecurity risk from the online trade in ornamental crayfish.

Trade in undomesticated ornamental animals has rapidly expanded beyond brick-and-mortar retail stores to now include growing numbers of internet marketplaces. The growing volume, diversity, and origins of invasive non-native species in trade challenge already weak national biosecurity policies. Despite widespread focus on vertebrates, many knowledge gaps exist regarding the online global trade of ornamental invertebrates. We conducted the first global assessment of the online trade in and associated invasion risk of freshwater crayfishes, which are increasingly popular aquarium animals. We systematically examined e-commerce marketplaces in multiple languages, scrapping information that included species identity, price, quantity, and shipping designation from each crayfish listing. Next, we combined geographic pathways of shipping associated with online trade (introduction risk) and environmental suitability modeling (establishment risk) to estimate global risk of non-native crayfish invasion risk. We identified hundreds of online marketplaces and thousands of sale listings in 33 countries (5 continents) involving 60 species and representing a selling value of ∼US$1.5 million. Invasion risk of non-native crayfish in trade was widespread, with geographic hotspots coinciding with both elevated opportunities for introduction (greater shipping offerings) and establishment. Precise characterization of the online species trade is fundamental to support new and reformed biosecurity policies, build industry partnerships, and design educational campaigns to prevent species invasions through trade. We found that the taxonomy, geography, and economics of the global online ornamental crayfish trade are vast and require greater attention.

Microplastic burden in native (Cambarus appalachiensis) and non-native (Faxonius cristavarius) crayfish along semi-rural and urban streams in southwest Virginia, USA

Our comparative assessment is the first study to investigate microplastic body burden in native (Cambarus appalachiensis) and non-native (Faxonius cristavarius) crayfish along a semi-rural and urban stream across different seasons. Crayfish, sediment, and surface water were collected, processed, and characterized using μRaman spectroscopy to compare microplastic polymer types and shapes across compartments. Average surface water concentrations were significantly higher in our urban stream compared to our semi-rural stream (17.3 ± 2.4 particles/L and 9.9 ± 1.3 particles/L, respectively; P = 0.015). Average sediment concentrations were similar between urban and semi-rural streams (140 ± 14.5 particles/kg and 139 ± 22.5 particles/kg, respectively; P = 0.957). Our findings showed a significant interactive effect of season, site, and nativity (i.e., species) regarding microplastic body burden in crayfish (P = 0.004). The smaller, non-native crayfish amassed more microplastic particles than the native crayfish (0.4–2.0 particles/g versus 0.4–0.8 particles/g, respectively). Fibers and fragments were the most common polymer shapes across compartments, with white and black being the dominant particle colors. Our study identified 13 plastic polymer types in crayfish and three in surface water and sediment; polypropylene was the most common polymer across compartments. This study provides evidence that crayfish body burden of microplastics can differ across species, seasons, and locations, highlighting the need for future studies to consider that sublethal impacts associated with microplastic body burden may vary by region and species.

Are long-term biomonitoring efforts overlooking crayfish in European rivers?

BackgroundLong-term biomonitoring of macroinvertebrates is a popular and valuable approach for assessing the status of freshwater ecosystems, identifying the impact of stressors, and evaluating ecosystem health. Although macroinvertebrate-based biomonitoring can be effective in detecting changes in distribution patterns and community trends over time, crayfish often remain undetected or unreported by biomonitoring efforts despite their importance in maintaining the functioning of aquatic ecosystems.ResultsBy analyzing a comprehensive database of long-term macroinvertebrate time series, we found that most sampling methods and assessment schemes can detect both native and non-native crayfish in running waters if sites are continuously sampled. However, native crayfish were detected to a lesser extent and by fewer methods. Kick-net sampling and assessment techniques prevailed as the most efficient methods for capturing crayfish. However, the substantial number of time series lacking crayfish data calls into question whether these methods are sufficiently comprehensive to encapsulate crayfish populations accurately. The use of other targeted methods such as baited traps or hand catching may provide a more reliable estimate of their presence.ConclusionsGiven the detrimental impacts of non-native crayfish and the decline in native crayfish populations, we strongly recommend that stakeholders and managers incorporate a combination of these approaches into their monitoring efforts. The use of different taxonomic levels (family vs. genus vs. species level) in estimating biological indices and biomonitoring tools can cause delays in identifying new non-native specie’s occurrences, hindering effective water quality assessment and ecosystem management by governments and stakeholders. Therefore, whenever possible, we call for standardized taxonomic levels for biomonitoring studies and management strategies to accurately address these issues and make recommendations going forward.

An overview of recent introductions of non-native crayfish (Crustacea, Decapoda) into inland water systems in Israel

An overview of recent introductions of non-native crayfish (Crustacea, Decapoda) into inland water systems in Israel

Modeling the habitat suitability of two exotic freshwater crayfishes in Mesoamerica and the Caribbean:Cherax quadricarinatus(von Martens, 1868) andProcambarus clarkiiGirard, 1852 (Decapoda: Astacidea: Parastacidae, Cambaridae)

AbstractBiological invasions are among the main threats to the diversity of freshwater ecosystems, particularly invasions of freshwater crayfishes, which have negatively impacted native populations and ecosystem functions. Various invasions of freshwater crayfishes have been relatively well documented, allowing the use of Ecological Niche Modeling (ENM) techniques to forecast their potential invasive distribution. Modeling the most environmentally suitable areas for exotic species can provide guidelines to allocate resources, thus contributing to the control and management of invasions. We modelled the potential distribution of Cherax quadricarinatus (von Martens, 1868) and Procambarus clarkiiGirard, 1852 in Mesoamerica and the Caribbean using global occurrence data and ten environmental variables to ensemble a model using nine different algorithms. Our models showed that C. quadricarinatus has a high probability of invasion in tropical lowland areas, with the presence of exotic populations of this species already reported. Our results support that P. clarkii has a higher probability of invasion in some of the mountain ranges and plateaus of the study region, where this species has already established non-native populations. These models visualize the high-risk areas of invasion of these two non-native crayfish species in Mesoamerica and the Caribbean. A regional approach for monitoring and control of the invasive populations is encouraged as well as regulations for trade and aquaculture of freshwater crayfishes.

Predation risk by largemouth bass modulates feeding functional responses of native and non-native crayfish

Context-dependency is prevalent in nature, challenging our understanding and prediction of the potential ecological impacts of non-native species (NNS). The presence of a top predator, for example, can modify the foraging behaviour of an intermediate consumer, by means of non-consumptive effects. This raises the question of whether the fear of predation might modulate consumption rates of NNS, thus shaping the magnitude of ecological impacts. Here, we quantified the functional feeding responses of three non-native crayfish species – red swamp crayfish Procambarus clarkii, rusty crayfish Faxonius rusticus and virile crayfish Faxonius virilis – compared to the native analogue signal crayfish Pacifastacus leniusculus, considering the predation risk imposed by a top fish predator, the globally invasive largemouth bass Micropterus salmoides. We applied the comparative functional response (FR) approach using snails as prey and exposing crayfish to water containing predator and dietary chemical cues or not. All crayfish species presented a destabilising Type II FR, regardless of the presence of chemical cues. Predation risk resulted in significantly longer handling times or lower attack rates in non-native crayfish; however, no significant differences were observed in signal crayfish. We estimated per capita impacts for each species using the functional response ratio (FRR; attack rate divided by handling time). The FRR metric was lower for all crayfish species when exposed to predation risk. Rusty crayfish demonstrated the highest FRR in the absence of chemical cues, followed by signal crayfish, virile crayfish and red swamp crayfish. By contrast, the FRR of signal crayfish was nearly twice that of rusty crayfish and virile crayfish and ten times greater than red swamp crayfish when chemical cues were present. The latter result agrees with the well-recognised ecological impacts of signal crayfish throughout its globally-introduced range. This study demonstrates the importance of considering the non-consumptive effects of predators when quantifying the ecological impacts of intermediate non-native consumers on prey. The direction and magnitude of the modulating effects of predators have clear implications for our understanding of NNS impacts and the prioritisation of management actions.

First record of Faxonius propinquus (Girard, 1852) in the Delaware River watershed and new records of another non-native crayfish species, Procambarus acutus (Girard, 1852)

First record of Faxonius propinquus (Girard, 1852) in the Delaware River watershed and new records of another non-native crayfish species, Procambarus acutus (Girard, 1852)

LIFE RIPARIAS Early Alert: Using GBIF-mediated data to better manage invasive alien species

Invasive alien species represent one of the major threats to biodiversity. Prevention is better than cure, but once invasive species get established, early management interventions are important to prevent further damage to nature and increasing management costs. Managers need to be informed as swiftly as possible when invasive species pop up in their area. Moreover, an effective response also requires information on species in neighbouring areas. This way, managers can anticipate recolonisation and coordinate the response across higher spatial scales. Open data are indispensible to efficiently organize such early detection of and rapid response to invasive species. Here, we present LIFE RIPARIAS Early Alert, a new open source tool that aggregates data from diverse sources and sends tailored e-mail alerts to managers. The tool focusses on the project area of the EU co-funded project LIFE RIPARIAS (Reaching Integrated and Prompt Action in Response to Invasive Alien Species, LIFE19 NAT/BE/000953), which aims to improve dataflows for the management of invasive alien species in river basins across regional administrative borders in Belgium. Data on invasive alien species in Belgium are scattered across a multitude of sources, including project surveys, official monitoring schemes, scientific projects and citizen science reporting portals. We facilitated the standardization and publication of these sources as open datasets to the Global Biodiversity Information Facility (GBIF). The early alert tool then harvests these observations from GBIF, visualizes them on a map as well as in table view, with their exact coordinates and a link to the original record. The tool allows for date range filtering and the selection of newly reported (and published) observations through a simple intuitive user interface. Users can create e-mail alerts to be notified of new observations for their species group(s), area(s) or source dataset(s) of interest. Currently, only observations from LIFE RIPARIAS target species (Branquart et al. 2022)—equally published as a checklist on GBIF—are displayed. These include non-native crayfish, invasive aquatic plants and a range of high-impact alert list species that should not yet occur in the area but will be rapidly removed should they arrive. The tool is currently being tested by the Belgian managerial community. In time, we hope to increase both the taxonomic scope as well as the number of sources. To our knowledge the RIPARIAS early alert tool is one of the first of its kind in Europe. It is unique in displaying data from multiple data sources at the highest spatial resolution, considering the species from the European Union Invasive Species Regulation (European Commission 2019) and actively promoting and supporting data owners to publish their data openly.

Dryland river restoration via carnivore reintroduction: Nonnative fauna dominate diets of river otters reintroduced to the Upper Rio Grande

Dryland rivers often harbor abundant populations of nonnative species that threaten native fauna and negatively alter ecosystem structure and function. Native semiaquatic carnivores, such as river otters (Lontra canadensis), that could predate nonnative fauna have been extirpated from many dryland rivers. During 2008–2010, river otters were reintroduced to the Upper Rio Grande (URG), a principal dryland river in the arid southwestern USA that has been colonized by dozens of nonnative fish and invertebrates. We conducted a scat-based food habits study and investigated whether otter reintroduction could be useful for managing nonnative aquatic fauna via predation. Across seasons, nonnative crayfish and fish were the dominant prey items in otter scats; crayfish frequency of occurrence was highest (61–95%), followed by nonnative suckers (7–26%) and trout (3–28%). After accounting for heterogeneous sampling effort between seasons, multi-level models estimated 0.77–0.93 probabilities that scats contained crayfish, compared to 0.05–0.21 and 0.03–0.14 probabilities for suckers and trout, respectively. Reintroducing river otters, and possibly other semiaquatic carnivores, to degraded dryland rivers might be an effective conservation action for controlling nonnative faunal populations within the biomic approach to river restoration, which could reestablish trophic cascades that improve ecosystem structure and function.

Physiological performance of native and invasive crayfish species in a changing environment: insights from Dynamic Energy Budget models.

Crayfish are keystone species important for maintaining healthy freshwater ecosystems. Crayfish species native to Europe, such as Astacus astacus and Austropotamobius torrentium, are facing decline and are increasingly endangered by changing climate and invasions of non-native crayfish, such as Pacifastacus leniusculus and Procambarus virginalis. The success of these invasions largely depends on differences in ontogeny between the native species and the invaders and how changes in the environment will affect the ontogeny. Dynamic Energy Budget (DEB) models can be used to investigate such differences because the models capture dependence of metabolism, and therefore ontogeny, on environmental conditions. We develop DEB models for all four species and investigate key elements of ontogeny and metabolism affecting interspecific competition. We then use the DEB models to predict individual growth and reproduction in current and new conditions that are expected to arise from climate change. Although observations suggest that P. leniusculus poses the major threat to native species, our analysis identifies P. virginalis, in spite of its smaller size, as the superior competitor by a large margin—at least when considering metabolism and ontogeny. Our simulations show that climate change is set to increase the competitive edge of P. virginalis even further. Given the prospects of P. virginalis dominance, especially when considering that it is able to withstand and spread at least some crayfish plague strains that severely affect native species, additional research into P. virginalis is necessary.

Introduction of Southern White River Crayfish (<i>Procambarus zonangulus</i>) to New Brunswick

Southern White River Crayfish (Procambarus zonangulus), an aquatic, potentially invasive species, is documented from New Brunswick for the first time. It was found in a small, privately owned, lake in the Saint John River system that was apparently stocked for recreational purposes with non-native fish and the crayfish. Procambarus zonangulus has successfully overwintered at the site for at least a year and, more likely, for several years. This is the third species of non-native crayfish recorded in New Brunswick, joining Spiny-cheeked Crayfish (Faxonius limosus) and Virile Crayfish (Faxonius virilis). This is also the first persisting introduction for the genus Procambarus in Canada of which we are aware.

Conservation genetics of the vulnerable stone crayfish using DNA barcoding and microsatellites

The stone crayfish Austropotamobius torrentium is a native European freshwater species with significant population declines caused by anthropogenic pressure onto its habitats, climate change and spreading of non-native invasive crayfish and their pathogens. Large-scale DNA barcoding based on sequencing a short fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene revealed this species represents a highly divergent taxon whose evolutionary heritage is preserved in genetically divergent mtDNA phylogroups, with majority of them having restricted distribution ranges. Guarding in mind vanishing populations trends and potential loss of genetic diversity, effective conservation planning and monitoring are needed for ensuring the persistence and long-term survival of this endangered species. Since genetic data are often critical for defining populations for conservation and management purposes, along with DNA barcoding, we employed microsatellites to examine samples of more than 400 individuals from 17 populations across its entire distribution range in Croatia, known as the stone crayfish diversity hot spot. Microsatellite analyses revealed high level of genetic diversity and differentiation among studied populations that grouped according to their geographical position and mtDNA phylogroup. Almost all sampled populations represent a distinct genetic cluster, showing high level of differentiation and reflecting long periods of isolation. Results of genetic characterisation enabled selection of suitable donor populations for future restocking and reintroduction programs. Combination of DNA barcoding and microsatellites provided good insight into genetic diversity and population structure as well as enabled sound conservation programs for this threatened species in Croatia.

Environmental nitrate impacts foraging and agonistic behaviours of invasive non-native crayfish (Pacifastacus leniusculus and Faxonius virilis)

Invasive species often co-occur in nature and positive or negative interactions among them can affect community structure and ecosystem functioning. Outcomes depend on the intrinsic traits of the species involved and on how species’ performance is affected by the environmental conditions of the recipient ecosystem. Here, we investigated the impact of nitrate, a nutrient common in urban and agricultural sewage discharges, on two invasive crayfish species (Pacifastacus leniusculus and Faxonius virilis) co-occurring in a Nitrate Vulnerable Zone in the UK. Crayfish were exposed to two ecologically relevant nitrate concentrations (≤ 10 and 50 mg NO3−/l) and seven traits relating to foraging success and interspecific interactions were assessed. During monospecific experimental trials, elevated nitrate had a similar impact on the foraging efficacy of P. leniusculus and F. virilis, reducing their ability to sense and find food. However, during dyadic interspecific competition experiments, higher nitrate caused a greater reduction in the number of aggressive behaviours of F. virilis towards P. leniusculus. As such, changes in environmental nitrate regime may affect interactions between these invasive species in regions of sympatry with consequences for their respective invasion dynamics and the wider ecosystem.

Selective fish passage: Restoring habitat connectivity without facilitating the spread of a non-native species

River managers are challenged to address two key threats to freshwater biodiversity. The first is the effects of habitat fragmentation by instream structures, such as dams and weirs, that disrupt migrations and impact species distributions. The second is the impact of non-native species on native species and ecological processes. However, mitigating anthropogenic habitat fragmentation through the installation of passage facilities can facilitate the invasion and spread of non-native species. This study compared the potential of two existing low-cost fish passage technologies designed for sloping weirs, a cylindrical bristle cluster (CBC) array and horizontally oriented studded tiles, to facilitate upstream movement of native European fish while preventing dispersal of non-native American signal crayfish (Pacifastacus leniusculus); thus providing a selective fish passage solution. Crayfish movement and passage was experimentally quantified at a Crump weir installed in a recirculating flume under two velocity regimes (low and high), without (control) and with the addition of either a CBC array or studded tiles. Results were compared to passage efficacy (PE) data for native fish species for both technologies (existing data). Most (84.4%) crayfish were active during the trials, exhibiting frequent up and downstream movements below the weir. During control conditions under the high velocity regime, high velocities (ca. 2.39 m s−1) prevented crayfish reaching the foot of the weir (PE: 0%). Under the low velocity regime, relatively low velocities (ca. 0.74 m s−1) at the weir crest prevented most crayfish from passing (PE: 10–16%). Crayfish movement speed and total distance moved were lower under the high than the low velocity regime. Neither fish pass technology improved crayfish maximum distance of ascent on the downstream weir face or PE under either velocity regime. Under comparable conditions to the high velocity regime tested here, previous studies have shown both technologies improve PE for native fish. Hence, both CBC arrays and studded tiles would likely function as suitable selective fish passes where the conservation objective is not to aid the spread of non-native crayfish. Additional passage inhibiting technologies will be required at sites where complete blockage of crayfish movement is required.

Simultaneous detection of native and invasive crayfish and Aphanomyces astaci from environmental DNA samples in a wide range of habitats in Central Europe

Crayfish of North American origin are amongst the most prominent high-impact invasive invertebrates in European freshwaters. They contribute to the decline of European native crayfish species by spreading the pathogen causing crayfish plague, the oomyceteAphanomyces astaci. In this study we validated the specificity of four quantitative PCR (qPCR) assays, either published or newly developed, usable for environmental DNA (eDNA) screening for widely distributed native and non-native crayfish present in Central Europe:Astacus astacus,Pacifastacus leniusculus,Faxonius limosusandProcambarus virginalis. We then conducted an eDNA monitoring survey of these crayfish as well as the crayfish plague pathogen in a wide variety of habitat types representative for Central and Western Europe. The specificity of qPCR assays was validated against an extensive collection of crayfish DNA isolates, containing most crayfish species documented from European waters. The three assays developed in this study were sufficiently species-specific, but the published assay forF. limosusdisplayed a weak cross-reaction with multiple other crayfish species of the family Cambaridae. In the field study, we infrequently detected eDNA ofA. astacitogether with the three non-native crayfish species under examination. We never detected eDNA fromA. astacitogether with native crayfish, but in a few locations eDNA from both native and non-native crayfish was captured, due either to passive transport of eDNA from upstream populations or co-existence in the absence of infected crayfish carriers ofA. astaci. In the study, we evaluated a robust, easy-to-use and low-cost version of the eDNA sampling equipment, based mostly on items readily available in garden stores and hobby markets, for filtering relatively large (~5 l) water samples. It performed just as well as the far more expensive equipment industrially designed for eDNA water sampling, thus opening the possibility of collecting suitable eDNA samples to a wide range of stakeholders. Overall, our study confirms that eDNA-based screening for crayfish and their associated pathogen is a feasible alternative to traditional monitoring.

The current distribution of the freshwater crayfish (Decapoda: Astacidae, Cambaridae) in the Neman river basin in Belarus

The trends in the distribution and occurrence of the freshwater crayfish in the water bodies of the Neman River basin are presents. It has been shown that both native species: the noble and the narrow-clawed crayfish are declined and/or are displaced with rapidly expanding its range the invasive spiny-cheek crayfish. In recent years the alien species was found in isolated gravel pits and lakes, where it could be transferred only by the human activity. These findings confirm the need of the education about the threats posed by the invasive species on the native biodiversity especially with the local community, which is an obligatory practice for protection the native species in the area expanded with non-native crayfish species. Further, to increase the likelihood of the local biodiversity conservation it is highly needed to undertake targeted actions aimed at resettling endangered populations into waterbodies unavailable for the invasive spiny-cheek crayfish expansion.

Hungary: a European hotspot of non-native crayfish biodiversity

There is a long history of crayfish introductions in Europe and numbers keep increasing. In Hungary, spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, red swamp crayfish Procambarus clarkii, marbled crayfish P. virginalis and Mexican dwarf crayfish Cambarellus patzcuarensis have become established. Here we report on monitoring at two localities with novel crayfish assemblages closely linked to releases associated with the pet trade. Florida crayfish Procambarus alleni were recorded from the Gombás brook near Vác living in syntopy with the established spiny-cheek crayfish. Dozens of Florida crayfish individuals including egg-carrying females have been detected. The short lifespan of this species and its documented presence including two overwintering in at least two years suggests possible establishment. However, the lack of juvenile records calls for further monitoring as long-term propagule pressure cannot be ruled out. We also identified a single marbled crayfish in the Danube floodplain at the end of the monitoring campaign. The second locality (Városliget thermal pond in Budapest) harbours an even more diverse crayfish assemblage. Here, we identified numerous red swamp and marbled crayfish in syntopy with dozens of monitored redclaws Cherax quadricarinatus and seven individuals of New Guinean Cherax species − C. holthuisi, C. snowden, as well as two scientifically undescribed species. These findings clearly indicate the attractiveness of urban and, especially, thermal waters for the release of even expensive aquatic pets and highlight the hitherto poorly known biodiversity of New Guinean crayfish species.

Divergence in foraging and predator avoidance behavior across the geographic range of native and non-native crayfish

There is growing evidence that species’ traits may diverge during biological invasions; however, we still lack a general understanding of how the invasion process affects behavior. We used a biogeographic approach to compare foraging and antipredator behavior across a reciprocal invasion (in which each species invaded the native range of the other) of virile (Faxonius virilis) and rusty crayfish (F. rusticus). We hypothesized that the invasion process would select for individuals that invest more in foraging and less in defense than their native counterparts. We used laboratory experiments to examine crayfish boldness, activity, and foraging voracity and mesocosm experiments to examine antipredator behavior in response to fish. Non-native virile crayfish (Indiana, USA) were less bold, active and voracious than native virile crayfish (Wisconsin, USA), and they exhibited more antipredator behavior. Non-native rusty crayfish (Wisconsin) were more active in mesocosms and exhibited less antipredator behavior than native rusty crayfish (Indiana). Combined, these findings suggest a growth/mortality trade-off. Counter to our hypothesis, relative investment in foraging versus predator avoidance differed across regions and was not consistently associated with native or invasive populations. Thus, the substantial divergence in behavior we observed may by driven by local adaptation.

Terrestrial emigration behaviour of two invasive crayfish species

To disperse between isolated waterbodies, freshwater organisms must often cross terrestrial barriers and many freshwater animals that are incapable of flight must rely on transport via flooding events, other animals or anthropogenic activity. Decapods such as crayfish, on the other hand, can disperse to nearby waterbodies by walking on land, a behaviour that has facilitated the spread of invasive species. Overland movement could play a key role in the management of non-native crayfish, though to what extent terrestrial emigration occurs in different species is poorly understood. Here, we directly compared the terrestrial emigration tendency of two non-native crayfish species in Great Britain; red swamp (Procambarus clarkii) and signal (Pacifastacus leniusculus) crayfish. We found that both species emigrated from the water and that there was no significant difference in terms of their terrestrial emigration tendency, suggesting that there is a risk both of these species will migrate overland and disperse to new habitats. This study shows that terrestrial emigration is an important behavioural trait to consider when preventing the escape of crayfish from aquaculture and further spread of invasive species.