Signal Crayfish (signal + crayfish)

Distribution by Scientific Domains


Selected Abstracts


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

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009
Damian H. Bubb
Abstract 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. [source]


Invasions and niche width: does niche width of an introduced crayfish differ from a native crayfish?

FRESHWATER BIOLOGY, Issue 8 2009
KARIN OLSSON
Summary 1. Human activities have promoted the spread of species worldwide. Several crayfish species have been introduced into new areas, posing a threat to native crayfish and other biota. Invader success may depend on the ability to utilise a wide variety of habitats and resources. Successful invaders are generally expected to have broader niches and to be more plastic than non-invasive species. 2. Using stable isotope ratios of carbon and nitrogen we compared the niche widths of native noble crayfish and introduced signal crayfish, a successful invader of Swedish streams. The calculation of niche width took account of between-site differences in basal resource isotope signature ranges. We also assessed whether population density, prey biomass or prey diversity affected niche width. 3. At the species level, signal crayfish had twice the niche width of noble crayfish. However, individual populations of noble crayfish and signal crayfish in Swedish streams had similar niche widths. This suggests that signal crayfish has greater plasticity with respect to habitat utilisation and feeding than noble crayfish. Niche width in both species correlated positively with benthic invertebrate biomass and diversity, indicating that animal food sources are important for crayfish. 4. We find that assessing niche width in relation to invader success can be a useful tool trying to predict the impact of invasions on different scales. The findings in this study suggest that invaders and natives will have a similar impact on the stream scale whereas the invader will have a larger impact on the regional scale due to the ability to utilise a wider range of streams. [source]


Non-lethal predator effects on the performance of a native and an exotic crayfish species

FRESHWATER BIOLOGY, Issue 12 2005
PER NYSTRÖM
Summary 1. I tested the hypothesis that the potential for non-lethal effects of predators are more important for overall performance of the fast-growing exotic signal crayfish (Pacifastacus leniusculus Dana) than for the slower growing native noble crayfish (Astacus astacus L.). I further tested if omnivorous crayfish switched to feed on less risky food sources in the presence of predators, a behaviour that could reduce the feeding costs associated with predator avoidance. 2. In a 2 month long outdoor pool experiment, I measured behaviour, survival, cheliped loss, growth, and food consumption in juvenile noble or signal crayfish in pools with either a caged predatory dragonfly larvae (Aeshna sp.), a planktivorous fish that do not feed on crayfish (sunbleak, Leucaspius delineatus Heckel), or predator-free controls. Crayfish had access to multiple food sources: live zooplankton, detritus and periphyton. Frozen chironomid larvae were also supplied ad libitum outside crayfish refuges, simulating food in a risky habitat. 3. Crayfish were mainly active during hours of darkness, with signal crayfish spending significantly more time outside refuges than noble crayfish. The proportion of crayfish outside refuges varied between crayfish species, time and predator treatment, with signal crayfish spending more time in refuges at night in the presence of fish. 4. Survival in noble crayfish was higher than in signal crayfish, and signal crayfish had a higher frequency of lost chelipeds, indicating a high level of intraspecific interactions. Crayfish survival was not affected by the presence of predators. 5. Gut-contents analysis and stable isotope values of carbon (,13C) and nitrogen (,15N) indicated that the two crayfish species had similar food preferences, and that crayfish received most of their energy from feeding on invertebrates (e.g. chironomid larvae), although detritus was the most frequent food item in their guts. Signal crayfish guts were more full than those of noble crayfish, but signal crayfish in pools with fish contained significantly less food and fewer had consumed chironomids compared with predator-free controls. Length increase of signal crayfish (35%) was significantly higher than of noble crayfish (20%), but signal crayfish in pools with fish grew less than in control pools. 6. This short-term study indicates that fish species that do not pose a lethal threat to an organism may indirectly cause reductions in growth by affecting behaviour and feeding. This may occur even though prey are omnivorous and have access to and consume multiple food sources. These non-lethal effects of predators are expected to be particularly important in exotic crayfish species that show a general response to fish, have high individual growth rates, and when their feeding on the most profitable food source is reduced. [source]


Time to establishment success for introduced signal crayfish in Sweden , a statistical evaluation when success is partially known

JOURNAL OF APPLIED ECOLOGY, Issue 5 2010
Ullrika Sahlin
Summary 1.,The signal crayfish Pacifastacus leniusculus is an invasive species in Sweden, threatening the red-listed nobel crayfish Astacus astacus through spreading the crayfish plague. Time-to-event models can handle censored data on such introduced populations for which the state (successful or not) is only partially known at the last observation, but even though data on introduced populations most often are censored, this type of model is usually not used for likelihood-based inference and predictions of the dynamics of establishing populations. 2.,We specified and fitted a probabilistic time-to-event model to be used to predict the time to successful establishment of signal crayfish populations introduced into Sweden. Important covariates of establishment success were found by the methods of ,model averaging' and ,hierarchical partitioning', considering model uncertainty and multi-colinearity, respectively. 3.,The hazard function that received the highest evidence based on the empirical data showed that the chances of establishment were highest in the time periods immediately following the first introduction. The model predicts establishment success to be <50% within 5 years after first introduction over the current distributional range of signal crayfish in Sweden today. 4.,Among covariates related to temperature, fish species and physical properties of the habitat, the length of the growing season was the most important and consistent covariate of establishment success. We found that establishment success of signal crayfish is expected to increase with the number of days when growth is possible, and decrease with the number of days with extremely high temperatures, which can be seen to approximate conditions of stress. 5.,Synthesis and applications. The results demonstrate lower establishment success of signal crayfish further north in Sweden, which may decrease the incentives of additional illegal introductions that may threaten the red-listed noble crayfish Astacus astacus. We provide a fully probabilistic statistical evaluation that quantifies uncertainty in the duration of the establishment stage that is useful for management decisions of invasive species. The combination of model averaging and hierarchical partitioning provides a comprehensive method to address multi-colinearity common to retrospective data on establishment success of invasive species. [source]


Competition for shelter among over-wintering signal crayfish and juvenile Atlantic salmon

JOURNAL OF FISH BIOLOGY, Issue 2 2004
S. W. Griffiths
Three separate effects on refuge use by signal crayfish Pacifastacus leniusculus and Atlantic salmon Salmo salar were examined: (1) the effect on Atlantic salmon of an addition of signal crayfish (doubling the total number of animals), (2) the effect on signal crayfish of an addition of Atlantic salmon and (3) intraspecific compared with interspecific competition, compared by holding total density of animals constant and varying the proportion of signal crayfish and Atlantic salmon in trials. Observations were made during winter, when both species are nocturnal. The proportion of Atlantic salmon sheltering was significantly lower in the presence than in the absence of signal crayfish when the interspecific treatment (Atlantic salmon plus signal crayfish) effected a doubling in density compared to the intraspecific treatment (Atlantic salmon alone). The proportion of signal crayfish sheltering was independent of the presence of Atlantic salmon. When total density was constant, the proportion of Atlantic salmon sheltering was significantly higher in intraspecific (52·8%) than interspecific trials (27·3%). Atlantic salmon out of shelter during the day in winter are believed to be very vulnerable to predators and the capacity for fish to share shelters with one another is known to be very low. Therefore, competition from crayfish for winter shelters may lead to detrimental effects on Atlantic salmon populations. [source]


Effects of bottom substrate and presence of shelter in experimental tanks on growth and survival of signal crayfish, Pacifastacus leniusculus (Dana) juveniles

AQUACULTURE RESEARCH, Issue 4 2003
R Savolainen
Abstract The effects of tank bottom substrates and presence of shelter on growth, survival and condition of cheliped in the juvenile (stage 2) signal crayfish, Pacifastacus leniusculus (Dana), with an initial stocking density of 200 individuals m,2 were investigated. In the first trial, three different tank bottom substrates with or without shelter were used. The three bottom types were loose gravel, glued gravel and bare bottom. The fastest growth both in terms of wet weight and carapace length was observed on loose gravel bottom. Also survival (range 30.1% to 49.8%) was affected by bottom type being higher on gravel bottoms than on bare bottom. Shelter improved survival only on loose gravel bottom. Bottom type influenced also the number of animals with cheliped injuries. The highest proportion of animals with no injuries (59.5%) was found on bare bottom and the proportion was about 12% and 13% units less on loose gravel and on glued gravel bottom. The presence of shelter had a marginal probability in increasing the number of animals without injuries. In the second trial, the substitution of ordinary gravel as tank bottom substrate with crushed limestone was studied. The mean final wet weights were 0.517 g on ordinary gravel bottom and 0.481 g on limestone bottom. The survivals were about 74% and 80% respectively. Limestone bottom decreased marginally final wet weight, and increased survival but did not affect the final carapace length that had a mean value of 13.6 mm. We conclude from the present experiments that the type of tanks and the rearing system used supported good growth of juvenile signal crayfish. The best growth results could be obtained by using loose gravel (or loose limestone) on the bottom of the tanks with a sufficient quantity of hiding places. However, there appears to be an increased risk for cheliped injuries on bottoms with loose materials. [source]


Detecting North American signal crayfish (Pacifastacus leniusculus) in riffles

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2010
Z. F. Gladman
Abstract 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. [source]


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

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2010
M. A. Freeman
Abstract 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. [source]


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

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009
Damian H. Bubb
Abstract 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. [source]