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ABSTRACT 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., 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)., 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., 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., 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. [ABSTRACT FROM AUTHOR]

Abstract: Assessment of population biology at early establishment stages is a fundamental component of conservation monitoring programmes, such as for invasive signal crayfish Pacifastacus leniusculus. Population structure, body condition (including its relation to density-dependence), spatial patterns and habitat relationships were examined between September and October 1997 along the lower River Stort catchment (Thames River catchment, UK). A higher proportion of females was observed at intermediate sizes, whereas the largest individuals were males. Body condition was positively associated with total crayfish abundance in females but not males. Principal components analysis of the population data (by gender and size) across sampling sites revealed three distinct groups (large males, large females, small crayfish of mixed gender), with large males having significantly (analysis of covariance) lower body condition. Multiple regression of crayfish population and habitat data revealed: increasing abundance was associated with high total suspended solids (e.g. burrowing behaviour) in all size/gender groups except medium and large males; decreasing abundances of large males and females with increasing hydrodynamic efficiency (i.e. Froude number); and increasing abundance of large males and females with increasing substratum roughness. Signal crayfish population structure in the River Stort suggests an elevated potential for dispersal and reinforcement throughout the River Lee catchment. The observed spatial and habitat segregation of crayfish by gender and size appears to reflect a female reproductive strategy that avoids contact between progeny and big aggressive/cannibalistic males. Furthermore, intra-male competition is the likely reason for the lower body condition of big males, given the lack of a negative relationship between male body condition and crayfish abundance. The comparison with established populations elsewhere shows that a sex-ratio biased towards females could be a good descriptor to detect invading populations. Potential threats posed by signal crayfish for the conservation of River Stort catchment are predation, competition and habitat alteration. [Copyright &y& Elsevier]

The aim of the study was to test for diel patterns in the diet and habitat use in a feral, pond-dwelling, non-native fathead minnow Pimephales promelas population in England. Fish were collected in June 2009 using traps set in four habitat types (open waters, rushes- Juncus effusus, weeds- Potamogeton natans and mixed vegetation), then sexed and measured for total length and eviscerated weight in the laboratory. Data were analysed at 6-h intervals, with Fulton's condition index and three dietary parameters (frequency of occurrence, number and weight) calculated. Minor diurnal differences in habitat use were observed in males, females and immatures, and these may be due to predator avoidance. Body condition varied greatly in rushes during daytime, probably due to shifts in habitat suitability (e.g. food, refuge). Detritus dominates the diet of native fathead minnow; however, planktonic crustaceans were the most important food resource for this population, with a clear ontogenetic shift, irrespective of habitat, towards greater proportion of ingested detritus in larger individuals. Overall, the results demonstrate that feral fathead minnows display substantial trophic plasticity and a wide range of habitat use, which is normally associated with invasive species. However, established fathead minnow populations in Europe are rare despite its wide-spread ornamental and scientific use. [ABSTRACT FROM AUTHOR]

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