Prospects for management strategies of invasive crayfish populations with an emphasis on biological control

• 1. The white‐clawed crayfish, Austropotamobius pallipes (Lereboullet), is the only freshwater crayfish indigenous to Great Britain and Ireland. It has a widespread, though declining distribution in England and parts of Wales but does not occur naturally in Scotland.
• 2. The North American signal crayfish, Pacifastacus leniusculus (Dana), is not native to Europe and was introduced to Britain in the 1970s. The signal crayfish out‐competes the native white‐clawed crayfish as it is larger and more aggressive. It is also responsible for the introduction and spread of crayfish plague, which has devastated white‐clawed crayfish populations in Europe.
• 3. Signal crayfish populations are causing significant changes to the equilibrium of native flora and fauna through increased grazing and predation pressures; they also contribute to habitat degradation through burrowing.
• 4. Manual removal of crayfish using traps and pond trials with biocides have met with moderate success in reducing crayfish numbers and containing populations. However, with new populations of signal crayfish being reported each year within the UK, there is now an urgent need to develop a strategy with which to eradicate or contain their spread.
• 5. Signal crayfish have populated many habitat types in the UK, each of which may require a different control strategy; hence no single strategy or universal solution is likely to be attainable.
• 6. Signal crayfish are susceptible to various biocides and microbial pathogens but significant scientific research will be required to develop safe biological control methods and integrated pest management (IPM) strategies to control these invasive organisms. Copyright © 2009 John Wiley & Sons, Ltd.

     

Detecting North American signal crayfish (Pacifastacus leniusculus) in riffles

• 1. The spread of the invasive signal crayfish (Pacifastacus leniusculus) outside its natural range is of widespread concern due to the threats posed to native biodiversity. To date, there is no standard protocol for determining signal crayfish presence or absence in a watercourse.
• 2. For the purposes of this investigation, the crayfish detection ability of active sampling methods — hand‐netting, electrofishing (one, two and three runs), kick sampling and Surber sampling — was tested at 30 sites along the River Clyde, southern central Scotland.
• 3. No single technique was successful in detecting crayfish in 100% of the sites known to contain crayfish and so the application of combinations of techniques was considered. The combination of techniques that resulted in a 100% detection rate was electrofishing (three runs) together with kick sampling. These results suggest that three‐run electrofishing and kick sampling are the best candidates for incorporation into a crayfish detection protocol.
• 4. The mean time taken to apply electrofishing (three runs) was significantly greater than the mean time to apply kick sampling. Given the lower effort required for its application, kick sampling is recommended as the preliminary technique: if kick sampling yields a negative result, the application of electrofishing will decrease the chance of recording a false negative presence. If both kick sampling and electrofishing fail to detect crayfish, trapping may further decrease the risk of a false negative result.
• 5. These findings have assisted in the development of a crayfish detection protocol, which will be applied across Scotland to determine the current distribution of signal crayfish. Copyright © 2010 John Wiley & Sons, Ltd.

     

Relative impacts of native and non‐native crayfish on shelter use by an indigenous benthic fish

• 1. The North American signal crayfish Pacifastacus leniusculus has been widely introduced throughout Europe where it is expanding its range and in many areas replacing the native white‐clawed crayfish Austropotamobius pallipes. There is concern with regards to the impact of this species replacement on benthic fish. Interspecific behavioural interactions and competition for shelter between the benthic fish, bullhead Cottus gobio and A. pallipes and P. leniusculus were measured to assess the comparative impact of native and non‐native crayfish.
• 2. Both white‐clawed crayfish and signal crayfish were dominant over bullhead. Bullheads moved away from approaches of crayfish, left shelters on entry of crayfish and rarely entered an occupied shelter. Signal crayfish made significantly more aggressive approaches towards bullheads than white‐clawed crayfish.
• 3. Alone, bullheads spent most of their time by day under shelter (median 96%), reflecting a highly entrained behavioural response, which was relaxed by night (median 60%). Both crayfish species reduced shelter use by bullheads although the extent of shelter sharing by bullheads was higher in trials with white‐clawed crayfish than with signal crayfish.
• 4. Sampling in the River Wharfe, northern England, where signal and white‐clawed crayfish and bullhead currently exist, demonstrated a negative relationship between the densities of signal crayfish and bullhead, with high bullhead abundance where crayfish were absent or where white‐clawed crayfish were present at low density.
• 5. Assuming that shelter is sometimes limited under natural conditions, crayfish are likely to displace bullheads from shelters, which may increase predation risk for bullheads. Although the effects of signal crayfish on bullhead shelter use were more intense, the pattern was highly evident for the native white‐clawed crayfish. The higher fecundity and densities attained by signal crayfish may be more significant than differences in the behaviour of the two crayfish species in determining the impact of crayfish on bullheads.

Copyright © 2008 John Wiley & Sons, Ltd.     

The decline of endangered stone crayfish (Austropotamobius torrentium) in southern Germany is related to the spread of invasive alien species and land‐use change

1. Declines in populations of stone crayfish (Austropotamobius torrentium) have recently been reported throughout many parts of their range, including southern Germany. To assess the rate of decline and the probable causes, a crayfish survey was conducted in the River Argen catchment, where the species was known to be widely distributed and abundant.
2. Using mixed‐effects regression analysis, the presence or absence of the species was subsequently correlated with riparian land‐use and habitat characteristics. To elucidate the potential role of crayfish plague in stone crayfish decline, the crayfish plague‐carrier status of newly discovered alien signal crayfish (Pacifastacus leniusculus) was evaluated using real‐time polymerase chain reaction (PCR).
3. Twenty‐five of the 98 surveyed sites were colonized by stone crayfish, including only 12 of 25 sites with a previous record. The probability of stone crayfish presence was positively correlated with overhanging bank structures and the proportion of broad‐leafed woods in riparian buffers. In contrast, high proportions of intensive grassland had a distinct negative effect on the probability of stone crayfish presence, and cropland also tended to decrease the probability of stone crayfish presence. Both land‐use forms have significantly increased in the study area within the last decade, signifying an intensification of riparian land‐use.
4. Plague‐carrying signal crayfish were present at two headwater sites. Crayfish plague transmission from highly resistant signal crayfish to highly susceptible stone crayfish has most likely contributed to the decline in stone crayfish, and crayfish plague outbreaks may account for up to 67% of the observed stone crayfish disappearances.
5. The present study confirms a marked decline in stone crayfish populations, which is probably driven by the persistent spread of invasive alien species and intensified riparian land‐use. Therefore, conservation efforts for stone crayfish should incorporate strategies to prevent and control the spread of invasive, plague‐carrying crayfish, and to mitigate pressures from land use.

Copyright © 2015 John Wiley & Sons, Ltd.     

Signal crayfish (Pacifastacus leniusculus) predation upon Atlantic salmon (Salmo salar) eggs

1. The signal crayfish (Pacifastacus leniusculus) is a large, polytrophic crustacean which has invaded waterways across much of Europe. Crayfish prey on the eggs of several fish species and egg predation, especially by invasive crayfish, is cited as a likely cause of population decline and a serious concern for the conservation of some fish species including at least one salmonid.
2. Numerically, crayfish populations may be dominated by small individuals, but most studies have investigated egg predation by large crayfish. Evidence for crayfish gaining access to buried fish eggs is equivocal.
3. The ability of signal crayfish of a range of age groups (and hence, sizes) to prey on unburied and buried Atlantic salmon (Salmo salar) eggs was investigated in laboratory experiments.
4. Only Age 2+ and older crayfish (24–43 mm carapace length (CL)) significantly reduced egg survival in unburied egg experiments, although some evidence of egg predation was observed with Age 1+ crayfish (16–22 mm CL). Age 0+ crayfish (8–14 mm CL) did not prey on salmon eggs. No evidence of substantial excavations or predation upon buried eggs by crayfish of any size class was observed. Binomial logistic regression of egg survival against crayfish CL indicated that mean egg recovery fell below control levels when CL exceeded 16.3 mm.
5. These results suggest that large signal crayfish are likely to pose the greatest threat to salmonid eggs, but that crayfish larger than 16.3 mm CL have the potential to prey on eggs.
6. Further research is needed before manual removal or harvesting of signal crayfish are used as conservation measures for Atlantic salmon spawning areas in which signal crayfish occur. Restoration of high‐quality salmonid spawning habitat might, however, help to prevent signal crayfish predation of salmonid eggs in addition to broader benefits for salmonid conservation.

© 2014 Crown copyright. Aquatic Conservation: Marine and Freshwater Ecosystems © 2014 John Wiley & Sons, Ltd.     

Time‐series analysis of native and non‐native crayfish dynamics in the Thames River Basin (south‐eastern England)

1. Monitoring is crucial for the conservation of endangered crayfish species as well as for managing and controlling invasive species. Yet, relatively few studies have assessed relationships between native white‐clawed crayfish Austropotamobius pallipes and non‐native signal Pacifastacus leniusculus, narrow‐clawed Astacus leptodactylus, virile Orconectes virilis and red‐swamp Procambarus clarkii crayfishes in freshwater environments at ecologically relevant spatial and temporal scales.
2. Thus, the present study examines the distribution dynamics of native and non‐native crayfishes in the River Thames Basin District (16 133 km², south‐eastern England) over four decades (1971–2010).
3. To reveal geographical bioinvasion and decline patterns, data on occurrences (sampling site, date) of native white‐clawed and four non‐native crayfishes were used to create sequences of decade maps for each species. Cumulative numbers of occupied grid squares were used to construct ‘invasion/decline’ curves and rates. To quantify dynamic features, the frequencies of survey occurrence for each species were subjected to time‐series analysis, followed by cross‐correlation to determine relationships between crayfishes.
4. White‐clawed crayfish was initially widespread, but gradually disappeared after the mid‐1970s, coinciding with the introduction and initial dispersal of signal crayfish. During 2001–2010 white‐clawed crayfish numbers declined steeply. Introduced in the mid‐1980s, narrow‐clawed crayfish spread within a few years, but is now restricted to the east of the basin, where virile and red‐swamp crayfishes were reported with low presence since their introductions in 2006. Dynamics of white‐clawed and signal crayfishes showed the opposing trends with a highly significant negative association.
5. Geographical patterns indicate that non‐native crayfishes were introduced in multiple locations in the study area. Recovery of native crayfish seems unlikely, given the impacts of signal crayfish and the continuing arrival of new crayfish species. This paper demonstrates the utility of using broad temporal and spatial scales for revealing accurate insights on invasion and decline dynamics.

Copyright © 2013 Crown copyright.     

Predation by invasive signal crayfish on early life stages of European barbel may be limited

1. To determine whether or not signal crayfish Pacifastacus leniusculus and native white‐clawed crayfish Austropotamobius pallipes prey on European barbel Barbus barbus eggs, interstitial free‐embryos and emergent larvae, experiments were undertaken in salmonid (substratum) incubators (six treatments, four controls) fitted with video recorders.
2. No corpses or remains of emergent barbel larvae or eggs, or parts thereof, were observed in any of the incubators containing buried eggs, and no emergent larvae showed any sign of attack. However, video evidence of a signal crayfish catching and consuming a barbel larva was obtained.
3. There were no statistically significant differences between white‐clawed and signal crayfish either in carapace length or weight at the beginning and end of the experiments. The conservation implications of these results are discussed.

     

Risk assessment for the Mexican freshwater crayfish: the roles of diversity,endemism and conservation status

1. The freshwater fauna has been judged to be one of the most threatened biotic components in the world. In many tropical‐temperate freshwater habitats worldwide the largest invertebrates are crayfish, as is the case with the cambarid crayfish in Mexico. With 98% of endemic species, most of them with reduced distribution ranges, the Mexican crayfish have not been analysed to examine how diversity, endemism and threat are distributed.
2. A data set was analysed containing 1419 locality records for the 56 species of crayfish occurring in Mexico arranged in a 251 cell grid. Spatial autocorrelation analyses using Moran's I and G* were conducted; species richness, endemism and threat indices were calculated and mapped. An integrated risk score was derived from the two indices.
3. Spatial autocorrelation analyses revealed a pattern that significantly departs from a random arrangement. Moran's I showed a positive autocorrelation between cells that are less than 800 km apart; while G* analysis identified one hotspot of diversity. Four areas with high endemism and seven areas with intermediate endemism values were recognized. The western portion of the Trans‐Mexican Volcanic Belt, and some areas in the north are of special concern owing to the presence of threatened microendemic species.
4. The areas where more threatened species occur differ from those with high endemism values. This distinction makes evident that for species with low dispersal capabilities the areas with high endemism are the product of historical and geological events, while the areas with high numbers of threatened species are those where human activities have had a major impact. The integrated risk score, however, resulting from the combination of endemism and threat, peaks along the Trans‐Mexican Volcanic Belt and where it joins the Sierra Madre Oriental.
5. The integrated risk score proposed in this study, based on well known and frequently used indices in conservation biology, can be used with existing data to determine areas where crayfish species richness, endemism and threat peak to make conservation efforts more cost‐effective.

© 2016 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons, Ltd.     

Ecology and conservation status of temporary and fluctuating ponds in two areas of southern England

• 1. A high proportion of ponds are temporary in nature, although the biodiversity value of such sites is still poorly recognized. This work explores the plant and macroinvertebrate communities of 76 temporary and fluctuating water bodies in two regions of southern England (Lizard Peninsula, Cornwall and New Forest, Hampshire) that have retained high pond densities. The ecology and conservation status of sites is examined, and comparisons made with ponds elsewhere in England and Wales.
• 2. Lizard and New Forest ponds supported 119 plant and 165 macroinvertebrate species respectively. Patterns of community similarity for plants and macroinvertebrates were highly concordant, taxa being related in a similar manner to measured environmental variables including pond area, depth, pH and water chemistry.
• 3. Patterns of pond occupancy revealed that most species were locally rare, over half occurring in less than 10% of ponds, and less than 10% being recorded from more than 50% of sites. More than 50% of ponds supported at least one nationally rare plant and almost 75% at least one nationally rare macroinvertebrate. These taxa occupied a wide range of pond types in each region, and did not have predictably different ecologies from common species.
• 4. Comparisons with ponds elsewhere in England and Wales revealed that Lizard and New Forest communities are nationally distinct, being most similar to ponds in areas of low intensity agriculture elsewhere in western Britain. Individual ponds in both regions supported more nationally rare taxa, on average, than ponds sampled in the national survey.
• 5. Ponds in the two areas have high conservation value, both regionally and nationally, supporting almost 75% of the global species richness of temporary ponds sampled across England and Wales. Within each region, many taxa are found in relatively few sites, and effective conservation of pond biodiversity will require a regional management approach.

Copyright © 2008 John Wiley & Sons, Ltd.     

Crayfish in central and southern Ukraine with special focus on populations of indigenous crayfish Astacus pachypus (Rathke, 1837) and their conservation needs

1. The thick‐clawed crayfish (Astacus pachypus Rathke, 1837) is the least studied indigenous crayfish species in Europe. Information about its distribution and biology is out of date by more than 15 years.
2. This study identified 94 localities with potential occurrence of thick‐clawed crayfish in eight southern and central regions of Ukraine, using questionnaire and literature analysis. Based on the information obtained, a field survey was conducted to examine and confirm the current distribution and abundance of crayfish species and evaluate basic water quality and habitat characteristics in each locality.
3. Details of density, sex ratio in the catches, health and moulting condition, threat level and water quality were identified for each population of A. pachypus.
4. Only four populations of this species were found, in lower parts of the Dnieper River, co‐occurring with Astacus leptodactylus Eschscholtz, in Kakhovka reservoir near Vesele village, two sites on the Dnieper River near Nova Kakhovka town and near Prydniprovske village, and one locality on the Dnieper's tributary – the Ingulec River near Sadove village.
5. Populations of thick‐clawed crayfish at three sites had low crayfish densities of 0.3–0.4 crayfish m^?2 or catch efficiency 0.2 crayfish per trap night. Only one locality on the Dnieper River, close to Nova Khakovka, had a stronger population with higher density (1.7 crayfish m^?2).
6. Healthy thick‐clawed crayfish inhabit larger water bodies with stable environments and good water quality. Female catch per unit effort was lower, and they had a higher percentage of chelae injuries compared with males.
7. All of the identified thick‐clawed crayfish populations are exploited by uncontrolled fishing for consumption and there is an urgent need for conservation of both the crayfish and their habitat.