Native Crayfish Research Articles

The Impacts of Invasive Crayfish and Other Non-Native Species on Native Freshwater Crayfish: A Review.

Freshwater crayfish are vital species in ecosystems where they naturally occur, as they hold keystone and ecological engineering positions in these systems. Non-native species are common and widely spread throughout Earth's freshwater ecosystems and can have severe impacts on native crayfish populations. There has yet to be a comprehensive global review of the impacts of non-native species on native crayfish. Two literature searches were conducted using Web of Science and Google Scholar to find articles to address four key aims: (1) summarise trends in the literature; (2) examine the mechanisms by which invasive crayfish impact native crayfish species; (3) examine the mechanisms by which other non-native species, such as fish, impact native crayfish species; and (4) identify gaps in knowledge and research priorities. This review highlights that a far greater amount of research has addressed the effects of invasive crayfish than other non-native species. The research on invasive crayfish focuses on four types of interactions with native crayfish: competition, predation, introduction of disease, and reproductive impacts. Studies addressing the impacts of other non-native species on crayfish indicate that predation and habitat destruction by these species are the key processes impacting native crayfish. It is evident that field-based research, particularly concerning competition between invasive and native crayfish, is limited. Therefore, further in situ research is needed to assess the validity of laboratory results in a natural setting. Additionally, in many cases, the impact of certain non-native species on native crayfish populations has gone unmonitored. For this reason, it is recommended that additional research focus on assessing the impact of these non-native species. To conclude, the impacts of invasive crayfish on native crayfish are profound and wide-ranging, often leading to population decline or extirpation. Further, other non-native species are also likely to have a highly deleterious impact on native crayfish populations; however, more research is required to understand the scope of this impact.

Impacts of invasion on a freshwater cleaning symbiosis

Organismal invasions have repeatedly been cited as a driving force behind the loss of biodiversity. Unlike many other impacts of invasion, the effect of invasion on native symbiont communities has received less attention. The introduction of invasive hosts presents a potential opportunity to native symbionts; invasive hosts could benefit native symbionts through providing a novel host environment that improves symbiont fitness relative to their fitness on native hosts. Alternatively, invasive hosts could noncompetent hosts for native symbionts, resulting in negative impacts on native symbiont abundance and diversity. Crayfish in the northern hemisphere host diverse assemblages of obligate annelid symbionts (P: Anellida, O: Branchiobdellida). Two invasive crayfish hosts in the genus Faxonius have been introduced and are interacting with the native crayfish hosts and their symbionts in three watersheds in western Virginia, USA. Previous studies suggest that the invasive host F. cristavarius is a less competent host for symbionts compared to native hosts in the genus Cambarus. We carried out an extensive survey in these watersheds to determine impacts of varying degrees of invasion on branchiobdellidan abundance and diversity. We also conducted a complementary host replacement experiment to investigate how increases in the relative abundance of invasive hosts contributes to observed patterns of symbiont abundance and diversity in the field. In our survey, as the proportion of invasive hosts at a site increased, branchiobdellidan abundance and diversity declined significantly. In the experiment, the worms dispersed onto both native and invasive hosts. As the percentage of noncompetent F. cristavarius hosts increased, the survival of branchiobdellidans declined. Both symbiont survival and opportunities for successful dispersal are reduced as this noncompetent invasive host progressively displaces native hosts, which imperils the integrity of native host-symbiont systems. Given that many native hosts accrue significant fitness benefits from their relationships with native symbionts, including hosts in our study system, losses of beneficial symbionts may produce a positive feedback loop that decreases invasion resistance of native species, exacerbates the effects of invasions, and presents a major conservation issue in invaded systems.

Characterising dispersal and potential impacts of non‐native red swamp crayfish (Procambarus clarkii) populations in the coastal plain region of the pee Dee River basin, U.S.A.

Abstract Non‐native species can spread rapidly through aquatic ecosystems in association with both natural and anthropogenic mechanisms, but the relative importance of these two mechanisms in determining the spread of a species is not always clear. The red swamp crayfish (Procambarus clarkii) has been introduced to multiple continents, including waterbodies in the United States where both natural and anthropogenic dispersal are likely to have contributed to its current distribution. The present study combined comparisons of historical and contemporary distributions of P. clarkii and several high conservation priority crayfish species, regional field sampling, and microsatellite‐based genetic approaches from the Pee Dee River basin in North Carolina and South Carolina to understand the dispersal patterns of P. clarkii and its potential effects on native crayfishes. Field sampling and microsatellite analyses revealed widespread populations of P. clarkii throughout the study area with catchment‐specific patterns of population genetic structure, wherein more distinct genetic structures were found in the basin with historic aquaculture activities and a longer period of occurrence. The rapid spread of P. clarkii has occurred concurrently with extirpations of populations of native crayfishes, namely the Waccamaw crayfish (Procambarus braswelli), the Carolina Sandhills crayfish (Procambarus pearsei) and the coastal plain crayfish (Procambarus ancylus). The rapid spread of P. clarkii and coincident extirpation of native crayfishes calls for more extensive regulatory controls to help prevent the intentional or accidental release of non‐native crayfishes through aquaculture practices, bait releases, the pet trade and the environmental education industry.

Prevalence of the crayfish plague pathogen in red swamp crayfish populations in western France: How serious is the risk for the native white-clawed crayfish?

The crayfish plague pathogen Aphanomyces astaci has been implicated in a number of mass mortalities and irreversible population declines of native crayfish across Europe. At present, the reservoirs of the pathogen in Europe are mainly populations of invasive North American crayfish species. In southwestern Europe, including France, a particularly widespread invader is the red swamp crayfish Procambarus clarkii. Recent distribution data confirm that P. clarkii is present in at least 75 French departments, i.e. more than 78% of those in metropolitan France. We analysed the prevalence and pathogen load of A. astaci in 42 populations of this species in western France (Nouvelle Aquitaine region), where the species is most densely distributed, particularly in a wide range of environments around the Gironde estuary. The pathogen was detected by two different quantitative PCR assays in more than three quarters of the populations studied (34 out of 42); 163 out of 480 analysed crayfish individuals tested positive for the presence of A. astaci. In most cases, individual infection levels were very low, detectable with quantitative PCR but not sufficient for pathogen genotyping. In seven P. clarkii individuals from four populations, however, we were able to assess A. astaci variation by microsatellite markers and sequencing of mitochondrial markers. All these host specimens carried A. astaci genotype group D, haplotype d1, which has caused the majority of crayfish plague outbreaks in neighbouring Spain. In contrast, the French outbreaks genotyped to date (including eight newly analysed in this study) were mostly caused by strains of genotype group B, specific to the signal crayfish Pacifastacus leniusculus. Haplotype d1 found in P. clarkii was involved in one of the newly characterised outbreaks. Our study confirms that P. clarkii is a potentially important reservoir of the crayfish plague pathogen in France, but not the main source of the pathogen in mass mortalities of A. pallipes, probably due to different ecological requirements of the different invasive host crayfish. However, as P. clarkii continues to spread, the threat posed by this species to native crayfish is likely to increase.

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.

High variation of virulence in Aphanomyces astaci strains lacks association with pathogenic traits and mtDNA haplogroups

Introduced into Europe from North America 150 years ago alongside its native crayfish hosts, the invasive pathogen Aphanomyces astaci is considered one of the main causes of European crayfish population decline. For the past two centuries, this oomycete pathogen has been extensively studied, with the more recent efforts focused on containing and monitoring its spread across the continent. However, after the recent introduction of new strains, the newly-discovered diversity of A. astaci in North America and several years of coevolution with its European host, a new assessment of the traits linked to the pathogen’s virulence is much needed. To fill this gap, we investigated the presence of phenotypic patterns (i.e., in vitro growth and sporulation rates) possibly associated with the pathogen’s virulence (i.e., induced mortality in crayfish) in a collection of 14 A. astaci strains isolated both in North America and in Europe. The results highlighted a high variability in virulence, growth rate and motile spore production among the different strains, while the total-sporulation rate was more similar across strains. Surprisingly, growth and sporulation rates were not significantly correlated with virulence. Furthermore, none of the analysed parameters, including virulence, was significantly different among the major A. astaci haplogroups. These results indicate that each strain is defined by a characteristic combination of pathogenic features, specifically assembled for the environment and host faced by each strain. Thus, canonical mitochondrial markers, often used to infer the pathogen’s virulence, are not accurate tools to deduce the phenotype of A. astaci strains. As the diversity of A. astaci strains in Europe is bound to increase due to translocations of new carrier crayfish species from North America, there is an urgent need to deepen our understanding of A. astaci’s virulence variability and its ability to adapt to new hosts and environments.

Environmental DNA can inform the trade‐off between proactive and reactive strategies for crayfish conservation

AbstractThe introduction of the signal crayfish Pacifastacus leniusculus to British rivers has led to ecological degradation and the decline of the native white‐clawed crayfish Austropotamobius pallipes. To manage and mitigate the impact of the signal crayfish, conservation agencies and government bodies employ multiple conservation strategies. These take the form of proactive native crayfish breeding and stocking programs and reactive invasive crayfish control programs. Here, we used eDNA to assess the populations of native and invasive crayfish species across 50 sites in 10 river catchments in Norfolk, United Kingdom (UK). The sites were chosen to enable assessment of the potential of eDNA to inform proactive and reactive crayfish conservation strategies. Three of the catchments sampled were selected to assess the success of recent A. pallipes reintroduction, whereas the remaining seven were selected to better understand the distribution of each species at the landscape scale. Combining results of eDNA‐based methods with net searches within an occupancy model enabled us to confidently determine the presence of P. leniusculus at eight sites, and A. pallipes at three sites, which was more than visual searches alone (five and two study sites, respectively). Neither eDNA nor net searches detected A. pallipes at sites where A. pallipes had been reintroduced. We recommend that practitioners using eDNA‐based surveys for management and conservation of crayfish should consider: (1) designing eDNA surveys with an emphasis on large spatial scales to comprehensively describe the distributions of native and invasive crayfish in a region of interest; (2) work with local conservation organizations and/or government bodies to inform the selection of study sites to generate results that are meaningful to real‐world conservation actions; and (3) use results from eDNA‐based crayfish surveys to target limited conservation resources to appropriate proactive and/or reactive conservation actions.

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.

The Crayfish Plague Pathogen Aphanomyces astaci in Ireland.

Crayfish plague is a devastating disease of European freshwater crayfish and is caused by the oomycete Aphanomyces astaci (Ap. astaci), believed to have been introduced to Europe around 1860. All European species of freshwater crayfish are susceptible to the disease, including the white-clawed crayfish Austropotamobius pallipes. Ap. astaci is primarily spread by North American crayfish species and can also disperse rapidly through contaminated wet gear moved between water bodies. This spread, coupled with competition from non-indigenous crayfish, has drastically reduced and fragmented native crayfish populations across Europe. Remarkably, the island of Ireland remained free from the crayfish plague pathogen for over 100 years, providing a refuge for A. pallipes. However, this changed in 1987 when a mass mortality event was linked to the pathogen, marking its introduction to the region. Fortunately, crayfish plague was not detected again in Ireland until 2015 when a molecular analysis linked a mass mortality event in the Erne catchment to Ap. astaci. Since then, the pathogen has appeared across the island. Between 2015 and 2023, Ap. astaci was detected in 18 water catchments, revealing multiple genotypes. Intriguingly, the pathogen in Ireland is present without its natural host species. The uneven distribution of various genetic lineages strongly suggests the human-mediated transport of zoospores via contaminated water equipment as a primary cause of spread. This review details the timeline of these events, Ap. astaci's introduction into Ireland, and its rapid spread. As well, this review references the genotypes that have been determined, and discusses the issue of non-indigenous crayfish species in Ireland and management efforts.

Valorizacija ljušture invazivnih rakova iz reke Dunav (Faxonius limosus) - ekstrakcija i karakterizacija proteina

In order to deal with invasive crayfish (Faxonius limosus) impact on the native crayfish, as well as fish biodiversity in the Danube River, a possible solution would be to find and adopt mechanisms for its utilization for novel valuable product production. Apart from utilizing edible parts for novel food products, the shell waste can also be considered a source of valuable compounds. The complex structure of the shell mainly consists of three basic compounds: chitin, protein and minerals-mainly calcium carbonate. In this study, shell waste proteins were extracted using three extraction methods. The first method involved using naturally present enzymes (proteases and lipases) in crayfish wastes to recover proteins through an autolysis process. To accelerate the process, UV radiation was used. The remaining two extraction methods were alkaline extraction of proteins, wherein one method alkaline extraction was applied directly to the shell waste, and the other method, alkaline extraction followed an acidic demineralization step of the shell waste. The obtained protein concentrates were analysed for yield, crude protein content, DPPH radical scavenging ability, amino acid content, and structure. The results have shown that a similar percentage of protein content was obtained by all three methods: 67.20-68.03 %, but the extraction yield was considerably different. Alkaline deproteinization with or without the step of demineralization resulted in a 9.20-10.98 % yield, while UV radiation accelerated autolysis resulted in only a 3.41 % yield. Although protein extraction without using exogenous enzymes or chemicals is a very interesting approach, a drawback of this approach is the low process yield. FTIR spectroscopy revealed a secondary structure that was similar in all three concentrates, according to peak deconvolution, with the autolytic concentrate differing to a lesser extent, showing a slightly higher share of b-sheet structures. The DPPH assay revealed high antioxidant activity of the concentrates (72.00-88.06 %), probably originating from active peptides derived from proteins and residual carotenoids, mainly astaxanthin.

English

Abstract The spread of invasive crayfish requires invaded habitats to be thermally suitable, and differences in thermal tolerances among species could provide thermal refugia for native crayfish affected by the invader. We estimated upper thermal tolerances for the invasive Faxonius hylas and native F. peruncus and F. quadruncus in Missouri, USA, using critical thermal maxima (CTmax) methodology to determine if there were ecologically exploitable differences in estimates among species and if areas within their distributional ranges exceed their thermal maximums. Estimates of CTmax did not differ among species or sexes but differed among groups acclimated to different temperatures. Additionally, crayfish size had a small, yet significant effect on CTmax estimates with smaller crayfish having lower CTmax estimates than larger crayfish. The similarity among CTmax estimates indicates that for at least upper thermal tolerance, areas thermally available to the native species will also be thermally suitable for the invader. We did not observe water temperatures in the field that exceeded CTmax estimates for any species. However, areas within the mainstem St. Francis River did have warming tolerance estimates of less than 5°C, indicating that establishment of the invader in the mainstem could be limited by water temperature.

Will the experimental population control of an invasive crayfish influence the diet and trophic position of a native crayfish? An assessment using stable isotopes

Context Trophic overlap between invasive and native species can cause a competitive displacement of the native. In Australian freshwaters, the invasive crayfish Cherax destructor has proliferated into the ranges of native Euastacus species. Aims To examine trophic overlap between C. destructor and the critically endangered Euastacus dharawalus and determine whether C. destructor population control causes shifts in the diet and trophic position of E. dharawalus. Methods We compared δ13C and δ15N values of tissue from both species collected from two sites. Population control of C. destructor was then conducted at one site, whereas the C. destructor population remained uncontrolled at the second site. The δ13C and δ15N values of E. dharawalus were then once again assessed. Key results Both species occupied similar trophic positions and consumed similar proportions of each food resource prior to control efforts. However, we found increases in the contribution of detritus to the diet of E. dharawalus following the removal of C. destructor, whereas no dietary shifts occurred at the uncontrolled site. Conclusions and implications The increase in detrital consumption suggests that control of C. destructor increased the availability of a preferred resource. Further, dietary competition between C. destructor and E. dharawalus is likely and reinforces C. destructor representing a substantial threat to Euastacus crayfish.

Detection of novel RNA viruses in wild noble crayfish (Astacus astacus): A virome analysis in Swiss water bodies

European native crayfish populations are undergoing a strong decline due to environmental factors and the introduction of highly competitive non-native species. Pathogens are an additional threat to native crayfish. However, aside from the crayfish plague, other infectious diseases are still widely unknown. This study aimed to investigate viruses present in seven populations of wild noble crayfish (Astacus astacus) in Switzerland, through high-throughput sequencing. Sequence analysis revealed the presence of 11 novel RNA viruses (one bunya-like, four hepe-like, two dicistro-like, three picorna-like, and one permutotetra-like) in the samples. The discovery of a novel bunya-like virus in noble crayfish without associated mortality or macroscopical alterations is of particular interest since it is closely related to the bunya-like brown spot virus, a virus described in 2019 from diseased native white-clawed crayfish (Austropotamobius pallipes) during a mass mortality event in France. It seems that these two closely related viruses have very different impacts on their respective hosts, raising the need for further investigations on virulence factors and host susceptibility towards these viruses. This study provides a basis for future investigations, permitting to gradually fill the knowledge gap in crayfish viral diseases.

Aphanomyces astaci in Mexico: A new haplotype from dwarf crayfish Cambarellus montezumae

The crayfish plague is an emerging infectious disease caused by the pathogen Aphanomyces astaci (Oomycota), which is responsible for the decimation of Eurasian freshwater crayfish. This pathogen can coexist with the North American crayfish. These are chronic carriers of the disease as consequence of an immune response that can contain the growth of the pathogen without killing it. The origin of A. astaci locates in the southeastern United States and coincides with the origin of the family Cambaridae. This diverse family of decapods is distributed in North America from southern Canada to Honduras. However, only the native crayfish species from Canada and the USA have been examined for the presence of A. astaci. In this study, we describe for the first time the presence of A. astaci in Mexico in a population of the native species Cambarellus montezumae. By analyzing the small (rrnS) and large (rrnL) mitochondrial ribosomal regions, we showed the presence of two haplotypes of A. astaci within the same population (d1-haplotype and, a novel haplotype that was named, mex1-haplotype). The finding of A. astaci in Mexico confirms the occurrence of this pathogen within the range of the family Cambaridae. The individuals of C. montezumae appear to be chronic carriers of A. astaci, indicated by the lack of documented crayfish plague outbreaks in this population, similar to the pattern observed in other North American species. Thus, the results are of special concern to susceptible species of southern regions of America, i.e., Parastacidae. Therefore, this work emphasizes the need to better understand the distribution and genetic diversity of A. astaci within the distribution range of the natural carriers, i.e., North American species, especially the unexplored area of the family Cambaridae.

Human Dimensions and Visitors’ Perspective in Freshwater Crayfish Conservation: The Case of a Protected Area in Italy

Human dimensions in endangered species conservation are often overlooked. However, including human dimensions in conservation projects can help conservationists integrate social and ecological dimensions and investigate individual or society’s perspectives toward conservation efforts. The aim of this study was to investigate how visitors of a protected area perceived the conservation of the native white-clawed crayfish (Austropotamobius pallipes), a species recently brought to disappearance by the introduction of the spiny-cheek crayfish (Faxonius limosus). From August to October 2017, we distributed a questionnaire to park visitors, aiming to: (i) identify behaviors that could affect the conservation of the native crayfish after reintroduction; (ii) investigate if visitors’ awareness and knowledge of native freshwater crayfish may increase approval for conservation initiatives. Of the 290 respondents, most (73%) had never heard of alien species. The respondents’ inclination to be favorable to resource investment and alien crayfish eradication and to perform specific educational training was significantly related to their knowledge of crayfish features. Knowledge of freshwater crayfish features resulted in being a main determinant in affecting visitors’ attitudes towards conservation initiatives. These results confirm that visitors’ awareness can increase approval for conservation programs and the importance of investigating the proper human dimensions before establishing management actions for endangered species.

Austropotamobius pallipes can be infected by two haplotypes of Aphanomyces astaci: A key example from an outbreak at an ex-situ conservation facility

The crayfish plague, caused by the pathogen Aphanomyces astaci, is a pandemic disease endemic to North America that has been devastating susceptible crayfish populations in Europe since the 19th century. In Spain, this disease has decimated populations of the native crayfish species Austropotamobius pallipes due to introductions of North American crayfish, which act as vectors of the pathogen. To combat against these losses, several regional governments have established ex-situ breeding programs to restock wild populations of the species. In this study, we report on an outbreak of A. astaci that occurred in one of the most important A. pallipes aquaculture centers in Spain. Using a variety of detection methods, we analyzed affected crayfish and environmental samples from the facilities over a period of six months and determined that the outbreak was caused by two haplotypes of A. astaci, d1 and d2, which are both associated with the North American crayfish species Procambarus clarkii. To our knowledge, this is the first report of a two-haplotype coinfection of A. astaci outside the native range of this pathogen.

Is Chemical Control for Crayfish in Hatchery Fish Shipments Practical?

AbstractInvasive crayfish (family Cambaridae) displace native crayfish species and alter aquatic habitat, community structure, and ecosystem function. We evaluated whether chemical control can be a reliable control agent for crayfish to ensure that shipments from fish hatcheries did not result in new infestations of invasive crayfish. A series of acute (≤1 h) toxicity tests were conducted to evaluate the toxicity of cypermethrin and pyrethrin to crayfish, freshwater mussels, and fish; chemical concentrations in test organisms; effectiveness of carbon‐block filters to remove cypermethrin from test waters; and the cost of chemical control relative to extra handling of fish. Cypermethrin dosed at 75 μg/L for 15 min resulted in 100% mortality of adult white river crawfish Procambarus acutus and virile crayfish Faxonius virilis but did not cause >20% mortality in adult pondmussel Ligumia subrostrata, juvenile fatmucket Lampsilis siliquoidea, fingerling Bluegill Lepomis macrochirus, hybrid sunfish (Bluegill × Green Sunfish L. cyanellus), hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), yearling Paddlefish Polyodon spathula, or ready‐to‐eat Bluegill, hybrid sunfish, and Channel Catfish Ictalurus punctatus. Behavioral effects, such as loss of equilibrium or head shaking, were generally limited to 1 h postexposure. Mean concentrations of cypermethrin increased in fish fillets (4–26 μg/g) and whole fish (5–1,770 μg/g); therefore, regulations limiting harvest for up to 7 d following stocking may be required. A carbon‐block filtration system was effective in reducing (<90%) cypermethrin concentrations and thus reducing potential effects to nontarget species in receiving waters. Extra handling of fish was more cost‐effective for all fish tested except for Paddlefish, where the cost of chemical control was half that for extra handling. For all other fish tested, chemical control was 4–10 times more expensive than extra handling. Special use permits or chemical registration are needed before chemical control for crayfish could be routinely used at fish hatcheries.

Distribution and habitat use of a rare native crayfish: Implications for conserving Data Deficient species

Abstract Few observations exist for the Kisatchie painted crayfish (Faxonius maletae), and little is known about its distribution, habitat use, or population structure. The lack of basic ecological data has led to a ‘Data Deficient’ designation, a category of conservation concern that is often overlooked for management actions. This work provides updated data and practical management suggestions for similarly Data Deficient species. Comprehensive (i.e. beyond known collection sites) crayfish surveys paired with habitat assessments across north‐east Texas were conducted. Among 74 survey sites in 10 counties within and adjacent to the known range for F. maletae, eight total crayfish species were encountered within 35 of these sites (47.3% of the total). Thirteen F. maletae individuals were collected across seven sites (9.5%). Notably, two individuals were found where the species had not been previously observed. Stepwise multiple logistic regression indicated that conductivity and availability of exposed root masses were positively related to F. maletae presence, although neither factor was statistically significant on its own. Neither nonmetric multidimensional scaling nor canonical correspondence analysis identified patterns between F. maletae presence and the presence of other crayfish species. Overall, F. maletae is geographically rare and occurs in exceptionally low abundance, challenging the ability to understand drivers of its distribution. However, given the depth of this survey, we can confidently say that F. maletae is no longer Data Deficient; rather, there is compelling evidence that it has a limited range and small population size. The Data Deficient versus rarity debate has wide‐reaching impacts on the conservation of aquatic taxa; species that are Data Deficient require heightened research focus in general, whereas rare organisms require targeted management to protect specific habitats. Furthermore, we suggest that future management efforts should focus on maintaining current populations through active monitoring to inform the potential habitat suitability of new areas for protection.

Distribution of Non-Indigenous Crayfish Species in Estonia and Their Impacts on Noble Crayfish (Astacus astacus L.) Populations

Invasive non-indigenous crayfish species (NICS) are a major threat to the existence of native crayfish populations in European freshwater ecosystems. The discovery of signal crayfish Pacifastacus leniusculus, marbled crayfish Procambarus virginalis, and spiny-cheek crayfish Faxonius limosus in Estonia has increased the risk of extinction of Estonia’s only native crayfish species, the noble crayfish Astacus astacus. The aim of this study was to give an overview of the status, distribution, and impacts of P. leniusculus, F. limosus, and Procambarus virginalis on A. astacus populations and assess the effect of trapping on NICS abundance. Annual monitoring of crayfish has been carried out since 2008 as part of A. astacus conservation and the NICS eradication plan. In this study, we present data from nine sampling locations monitored from 2010 to 2022. The spread of NICS continues to increase beyond their distribution areas, and in two sampling locations P. leniusculus and A. astacus live in sympatry. Our results suggest that trapping has a limited effect on population abundance, as NICS have already caused the extinction of two A. astacus populations. However, intensive trapping should continue simultaneously with sensitive molecular techniques to monitor the spread of NICS.

An invasive species revisited: Continued displacement of native crayfishes by the invasiveFaxonius rusticus(Girard, 1852) (Decapoda: Astacidea: Cambaridae) in Illinois after 25 years

AbstractSince 1995 Faxonius rusticus (Girard, 1852) has continued to expand its range in Illinois, USA and cause displacement of native crayfishes. We revisit five historic collection sites for F. rusticus made by C.A. Taylor and M. Redmer in 1995 and compare densities of F. rusticus with native sympatric crayfish species to document changes over the past 25 years. We additionally compiled data from vouchered specimens and update the range of F. rusticus in Illinois. Data from the five density sites indicates that F. rusticus is still common and displacing sympatric crayfish at four of the five sites. Since 1995 F. rusticus has been collected at 137 new sites including range expansions west and south in Illinois. It now has been collected from one-third of Illinois drainages. Recent evidence has provided a cause for optimism as in some areas F. rusticus populations are declining. Without proper monitoring and management F. rusticus will continue to spread in Illinois waters.