We assessed the xtent of temporal variation and autocorrelation in fish habitat use based on an experimental study of individual 0+ juvenile barbel, Barbus barbus, in an artificial flume. Five treated and five control fish were individually subjected to an increase in discharege (intervention) hlfway through each experiment and kept at baseline discharge throughout, respectively. Preference surves for velocity were generated for each of 60 trials per experiment and for each combination of treated/control (fish) x before/after-intervention. There were large between- and within-individual differences in velocity preference, both in treated and in control fish. Most barbel explored the entire range of velocities, whereas some individuals used a more limited range. Temporal variation in behavioural responses was assessed by a PCA-based methodology. Autocorrelation (i.e. correlation between sequential trials) was diagnosed in most response profiles, supporting recent fidings that individuals may have a "memory" of their past velocity usage. The relevance of the results for numerical habitat models of fish habitat assessment is discussed, as well as the importance of incorporating temporal variability into fish habitat use models (e.g. PHABSIM), not only as ontogenetic intervals but also as longitudinal data of individual behaviours. A warning is also re-issued about the erroneous belief of "pseudoreplication" simly arising from repeated measurements in time.
The record is confirmed of a “Clariobranchus” hybrid Clarias gariepinus × Heterobranchus sp. specimen in the River Danube in Croatia. Clarias gariepinus was introduced to Europe for farming and research purposes. Because of their faster growth and short time to achieve market size, “Clariobranchus” hybrids have gained attention in European aquaculture. To date, no record has been found in the literature of “Clariobranchus” hybrid escapees in inland waters of Europe. The present finding suggests that the “Clariobranchus” hybrid escaped from an unprotected aquaculture system or open pond farm. The threat of establishment of a population of this hybrid in suitable environments, such as thermal ponds, cannot be ruled out.
Growth in length and weight, based on a combination of scale annulus interpretation and back-calculation using the Fraser-Lee model, was studied in male and female barbel, Barbus barbus, from a section of the River Jihlava sampled in 1999–2001. Results were compared with growth data obtained with similar methods in 1976, prior to construction and functioning of a hydropower scheme complex, and during the period of the scheme’s partial operation (1980–1984). Recent growth rate, under seemingly fully-stabilised environmental conditions and complete adaptation of the barbel population, showed the highest distinct sexual dimorphism in growth rate was also confirmed, with females growing faster than males, though to a lower extent than recorded both during previous periods and from several other localities. Further, upon comparison of back-calculated lengths for previous years of recently tagged-and-recaptured fish (1999–2001) with observed lengths directly measured at corresponding ages, no significant differences were overall found between the results obtained by either method in most age groups. Finally, the linear Fraser-Lee model proved a sufficiently accurate and practical method for back-calculating lengths for previous years of life also in barbel.
We studied movement and abundance of barbel, Barbus barbus , over three years (October 1995 to September 1998) in two stretches (Woolmer’s Park, Holwell Bridge) of a section of the River Lee (Hertfordshire, England) delimitated by water retention structures. Of 349 tagged individuals (168 at Woolmer’s Park; 181 at Holwell Bridge), 51.8 % and 13.3 % respectively were recaptured at least once, with a much higher rate of multiple recaptures at Woolmer’s Park, where monitoring of movements was over a longer period, than at Holwell Bridge, where too few recaptures were made for further movement analysis. At Woolmer’s Park, 77.1 % of the barbel showed limited (i.e. resident component) and the rest greater between- capture movements (i.e. mobile component). There was no preferential directional movement across size classes. Based on the available recapture data, population size (estimated through a Bayesian method) first increased moderately (1995–96) and then sharply (1996–97) at Woolmer’s Park, and even further later at Holwell Bridge (1998–99). This may reflect a recovery phase in the local population, or possibly a rising part of a cyclic recruitment pattern, such as reported for barbel elsewhere and for other cyprinids in the UK. Habitat enhancement is recommended over stocking, given the adequate abundance of barbel in areas with suitable habitat. However, it remains unclear whether fencing-off of the banks from livestock will enhance 0+ barbel numbers, which appear to be low relative to some European rivers of similar width and depth.
The risk screening of non-native species that are likely to be invasive in a defined risk assessment area is crucial for implementing strategies of rapid response and mitigation to protect native biodiversity and socio-economic activities. However, for successful risk-ranking of the screened species, scientifically defensible evidence in support of the screening outcomes must be provided, and computation of a correctly calibrated threshold to distinguish between medium-risk and high-risk species must be achieved. This paper reviews published applications of the “second-generation” Weed Risk Assessment-type decision support tools (i.e. the Aquatic Species Invasiveness Screening Kit and the Terrestrial Animal Species Invasiveness Screening Kit) and evaluates them in terms of the above two requirements. Several procedural errors were identified that involved: i) lack of provision of the report with details of the species-specific screenings; ii) incomplete justifications for the responses in the toolkit questionnaire; iii) incomplete details of the protocol used for the a priori categorisation of the screened species for threshold computation; iv) unaccepted or non-existent taxonomic names for the screened species (including typographical errors). Guidelines are provided for both assessors and reviewers to ensure that these procedural errors are avoided in future applications of these risk screening toolkits.