The impact of introduced signal crayfish Pacifastacus leniusculus on stream invertebrate communities

• 1. The effect of a newly introduced population of signal crayfish (Pacifastacus leniusculus) on a riverine invertebrate community in the River Clyde, Scotland, is examined. Five hypotheses related to crayfish impact on the invertebrate community are tested by comparing sites containing signal crayfish with similar sites in the same river which have not yet been colonized.
• 2. The hypothesis that crayfish significantly reduce the total numbers of invertebrates in the community was supported by this study, with invertebrate density in areas containing signal crayfish around 60% of that with no observed crayfish.
• 3. The hypothesis that crayfish presence affects some groups more than others was also supported. Plecoptera, Chironomidae, Diptera and Hirudinea, in particular, showed evidence of reduced species numbers in areas containing crayfish, and Plecoptera, Hirudinea, Tricladida and Hydracarina showed evidence of reduced densities. Community diversity and richness was also lower at sites containing crayfish.
• 4. Neither the hypothesis that overall invertebrate biomass would be lower at sites with crayfish present nor the hypothesis that individual invertebrate size would be lower at sites with crayfish was supported.
• 5. Overall the study indicates that introduced signal crayfish can significantly and fundamentally modify fluvial macroinvertebrate community structure.

Copyright © 2006 John Wiley & Sons, Ltd.     

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.

     

Underwater video analysis as a non‐destructive alternative to electrofishing for sampling imperilled headwater stream fishes

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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.     

Using occupancy models to assess the effectiveness of underwater cameras to detect rare stream fishes

1. Many conservation efforts for freshwater fishes have been undertaken; however, continuing the monitoring of both the distribution and the abundance of species to determine the effectiveness of these actions can be difficult. As species increase in rarity, they are more difficult to detect in the field, making inferences on occupancy less reliable.
2. Conventional sampling methods, such as electrofishing and seining, require the physical handling of rare fishes, which may cause stress and mortality and, consequently, compromise conservation goals and limit monitoring programmes. Non‐invasive surveillance methods, including underwater video, are playing an increasingly important role.
3. In this study, occupancy models were used to estimate the detection probability of underwater cameras as an alternative to the conventional sampling methods for rare stream fishes. Redside dace (Clinostomus elongatus), a small minnow listed as Endangered, was used as a model organism for rarity. A total of 69 historical redside dace sites were sampled using three sampling methods to determine the effect of gear type on detecting and identifying the habitat preferences of this rare minnow.
4. On average, using multiple underwater cameras is as effective at detecting a rare minnow as conventional sampling methods (backpack electrofisher and seine) and causes no harm.
5. The detection probability of both underwater cameras and backpack electrofishing were adversely affected by turbidity, whereas seining was positively affected by stream velocity. The probability of occupancy of redside dace is driven by open channels and sediment size, and this provides a strong basis for informing stream restoration projects.
6. The use of multiple underwater cameras over conventional sampling methods is recommended when sampling for rare and endangered minnows in systems with low turbidity.

     

Comparison of traditional and environmental DNA survey methods for detecting rare and abundant freshwater fish

1. Detecting rare species is often a necessity for conservation and management, yet challenging for many field survey methods. Environmental DNA (eDNA) is a highly promising solution that has been shown to outperform many established survey methods.
2. Macquarie perch (Macquaria australasica) is an endangered native species that has declined significantly in range and abundance. Detection of M. australasica was compared with an abundant alien fish species (Oncorhynchus mykiss) using eDNA and three conventional survey methods: gill nets, electrofishing and fyke nets.
3. eDNA occupancy estimates for both fish species were compared using four different models to investigate what effect these differences have on false positives and false negatives for the rare and common fish species. These models used unadjusted eDNA detections in water samples, eDNA detections that have been screened using a limit of detection method to remove potential false positives, eDNA data supplemented with a second survey method, or eDNA data augmented with sequencing of positive polymerase chain reaction replicates.
4. eDNA surveying as a single detection method was found to be more efficient and sensitive compared with each capture method separately and combined. Occupancy estimates for the common and rare species did not vary significantly between the four site occupancy-detection models, suggesting that supplementary data may not have as much effect on occupancy estimates compared with other approaches such as temporal or spatial sampling.
5. We conclude that eDNA outperforms the three established survey methods for both a rare and common freshwater fish species. Although there was no significant effect of augmenting eDNA survey methods with other survey data, additional data may improve confidence in detection, and provide confirmatory evidence for unexpected or new detections of a species.

     

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

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

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

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Fish biodiversity sampling in stream ecosystems: a process for evaluating the appropriate types and amount of gear

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Defining critical habitat conditions for the conservation of three endemic and endangered cyprinids in a Mediterranean intermittent river before the onset of drought

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Investigating the threat of non‐native North American signal crayfish (Pacifastacus leniusculus) to salmon redds

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

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Longitudinal distribution of uncommon fishes in a species‐rich basin

1. The spatial organization of fishes in a river system was investigated to evaluate the longitudinal distribution of uncommon species. It was anticipated that overall richness of the fish community would increase in a downstream direction together with habitat extent, but that more uncommon species would occur upstream owing to greater heterogeneity among sites.
2. Fish were collected between 1995 and 2014 at 85 sites distributed throughout the Duck River Basin, Tennessee, USA. A site usually consisted of four habitat types: riffles, runs, pools and shoreline. Each habitat type was sampled with a multipass electrofishing protocol.
3. In all, 136 native fish species were collected. Of these, 71% were classified as uncommon but represented only 16% of the total count of fish collected. As expected, overall species richness increased downstream, but contrary to expectation, uncommon species did too. Some uncommon species were restricted exclusively to tributaries and headwaters, some to tributaries and mainstem, many to mainstem only, but the largest fraction of uncommon species occurred throughout the basin, but even this last group increased in richness downstream.
4. Conservation often focuses on uncommon species. This study suggests that a greater number of uncommon species can be conserved with an emphasis on large downstream reaches, which not only include more aquatic habitat to support larger concentrations of fish, but also shelter the uncommon species that tend to require the most protection.

     

The relationship between water quality and indigenous and alien crayfish distribution in the Czech Republic: patterns and conservation implications

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

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A method test of the use of electric shock treatment to control invasive signal crayfish in streams

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Amphibian conservation in Scotland: A review of threats and opportunities

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The North American signal crayfish,Pacifastacus leniusculus (Dana), established in the wild in Scotland

1. Although the North American signal crayfish, Pacifastacus leniusculus (Dana), has been brought into Scotland for aquaculture several times in the past, there appears to be no record of it ever having become established in the wild here. 2. The species is now recorded as being well established at a stream site in south-west Scotland where many specimens were collected in the summer of 1995. Local information indicates that the species has occurred there for several years. 3. The significance of this record is that Scotland is no longer free from this aggressive and invasive species. Fortunately, this locality is far away from the only population of the native white-clawed crayfish Austropotamobius pallipes (Lereboullet), an introduced stock which has been long established in north-west Scotland.