Interactions between landscape and local factors inform spatial action planning in post-fire forest environments

Landscape Ecology - Landscape and local factors govern tree regeneration across heterogeneous post-fire forest environments. But their relative influence is unclear—limiting the degree that...     

An assessment of the variation in the prevalence of renal myxosporidiosis and hepatitis in wild brown trout, Salmo trutta L., within and between rivers in South-West England

The prevalence of renal myxosporidiosis in wild brown trout, Salmo trutta, in seven river catchments in South-West England was investigated. Three hundred and twenty-seven fish were sampled from 16 sites, of which 54 (16.5%) were found, by histological examination of the kidney, to be infected with Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease. No T. bryosalmonae infected fish were found in one river catchment, in other catchments the prevalence ranged from 2.5% to 36%. Hepatitis was strongly associated with the presence of T. bryosalmonae (odds ratio = 20.2, P < 0.001). Chloromyxum schurovi was found in 25% of fish and in six of seven river catchments, where the prevalence ranged from 2.4% to 63%. There was a strong negative association between the presence of T. bryosalmonae and C. schurovi (odds ratio = 0.10, P < 0.001). A hierarchical binomal model of the variance indicated that for T. bryosalmonae most of the variance existed at the site level, whereas for C. schurovi most variance existed at the river catchment level, suggesting that prevalence of T. bryosalmonae infection is determined largely by site level factors (e.g. presence of alternate host). The intraclass correlation coefficients (ICC) were 0.2 and 0.4 for T. bryosalmonae and C. schurovi, respectively, indicating the latter has higher effective transmission because of a higher level of infectiousness and/or abundance of alternate oligochaete hosts. These values can be used in future studies to estimate the sample sizes required to generate prevalence estimates with the required precision.     

Qualitative risk assessment of routes of transmission of the exotic fish parasite Gyrodactylus salaris between river catchments in England and Wales

Gyrodactylus salaris is a freshwater, monogenean ecto-parasite of Atlantic-salmon. Infection of its natural host, the Baltic strain of Atlantic-salmon, is inapparent. G. salaris also can infect rainbow-trout (Oncorhynchus mykiss) permanently, and cause infection of ≤50 days in several other species. It is only on Atlantic stocks of Atlantic-salmon (Salmo salar) that the parasite multiplies unchecked by an immune response, causes death in juveniles and dramatic reductions in wild populations. In Norway, the parasite has been introduced into 45 rivers, resulting in reductions in Atlantic-salmon stocks of up to 98%. It is probably the most-important exotic fish-disease threat to the UK. We used risk analysis to assess the most-important routes of spread for G. salaris between rivers in England and Wales. The movement of live rainbow-trout was identified as the most-important route of transmission; this route is likely to lead rapidly to the wide geographic spread of the parasite. The movement of other species of fish (especially from sites holding rainbow-trout) is also an important risk. Other routes of spread (including mechanical transmission on farm equipment and vehicles, angling equipment, canoes, etc.) might allow limited local spread (mainly to neighbouring rivers).     

Voracious invader or benign feline? A review of the environmental biology of European catfish Silurus glanis in its native and introduced ranges*

A popular species for food and sport, the European catfish (Silurus glanis) is well‐studied in its native range, but little studied in its introduced range. Silurus glanis is the largest‐bodied freshwater fish of Europe and is historically known to take a wide range of food items including human remains. As a result of its piscivorous diet, S. glanis is assumed to be an invasive fish species presenting a risk to native species and ecosystems. To assess the potential risks of S. glanis introductions, published and ‘grey’ literature on the species’ environmental biology (but not aquaculture) was extensively reviewed. Silurus glanis appears well adapted to, and sufficiently robust for, translocation and introduction outside its native range. A nest‐guarding species, S. glanis is long‐lived, rather sedentary and produces relatively fewer eggs per body mass than many fish species. It appears to establish relatively easily, although more so in warmer (i.e. Mediterranean) than in northern countries (e.g. Belgium, UK). Telemetry data suggest that dispersal is linked to flooding/spates and human translation of the species. Potential impacts in its introduced European range include disease transmission, hybridization (in Greece with native endemic Aristotle’s catfish [Silurus aristotelis]), predation on native species and possibly the modification of food web structure in some regions. However, S. glanis has also been reported (France, Spain, Turkmenistan) to prey intensively on other non‐native species and in its native Germany to be a poor biomanipulation tool for top‐down predation of zooplanktivorous fishes. As such, S. glanis is unlikely to exert trophic pressure on native fishes except in circumstances where other human impacts are already in force. In summary, virtually all aspects of the environmental biology of introduced S. glanis require further study to determine the potential risks of its introduction to novel environments.     

Ranking freshwater fish farms for the risk of pathogen introduction and spread

A semi-quantitative model is presented to rank freshwater rainbow trout farms within a country or region with regards to the risk of becoming infected and spreading a specified pathogen. The model was developed to support a risk-based surveillance scheme for notifiable salmonid pathogens. Routes of pathogen introduction and spread were identified through a process of expert consultation in a series of workshops. The routes were combined into themes (e.g. exposure via water, mechanical transmission). Themes were weighted based on expert opinion. Risk factors for each route were scored and combined into a theme score which was adjusted by the weight. The number of sources and consignments were used to assess introduction via live fish movements onto the farm. Biosecurity measures were scored to assess introduction on fomites. Upstream farms, wild fish and processing plants were included in assessing the likelihood of introduction by water. The scores for each theme were combined to give separate risk scores for introduction and spread. A matrix was used to combine these to give an overall risk score. A case study for viral haemorrhagic septicaemia is presented. Nine farms that represent a range of farming practices of rainbow trout farms in England and Wales are used as worked examples of the model. The model is suited to risk rank freshwater salmonid farms which are declared free of the pathogen(s) under consideration. The score allocated to a farm does not equate to a quantitative probability estimate of the farm to become infected or spread infection. Nevertheless, the method provides a transparent approach to ranking farms with regards to pathogen transmission risks. The output of the model at a regional or national level allows the allocation of surveillance effort to be risk based. It also provides fish farms with information on how they can reduce their risk score by improving biosecurity. The framework of the model can be applied to different production systems which may have other routes of disease spread. Further work is recommended to validate the allocated scores. Expert opinion was obtained through workshops, where the outputs from groups were single point estimates for relative weights of risks. More formal expert opinion elicitation methods could be used to capture variation in the experts' estimates and uncertainty and would provide data on which to simulate the model stochastically. The model can be downloaded (in Microsoft(?)-Excel format) from the Internet at: http://www.cefas.defra.gov.uk/6701.aspx.     

Epizootic haematopoietic necrosis virus—An assessment of the likelihood of introduction and establishment in England and Wales

Epizootic haematopoietic necrosis virus (EHNV) is an iridovirus that affects perch (Perca fluviatilis) and rainbow trout (Oncorhynchus mykiss). It emerged in Australia in the 1980s and has not been discovered elsewhere. It causes a high level of mortality in perch resulting in steep population declines. The main possible routes of introduction of the virus to England and Wales are the importation of infected live fish or carcasses. However, no trade in live susceptible species is permitted under current legislation, and no importation of carcasses currently takes place. The virus is hardy and low levels of challenge can infect perch. Therefore, mechanical transmission through the importation of non-susceptible fish species should be considered as a potential route of introduction and establishment. Carp (Cyprinus carpio) have been imported to the UK from Australia for release into still-water fisheries. A qualitative risk assessment concluded that the likelihood of EHNV introduction and establishment in England and Wales with the importation of a consignment of carp was very low. The level of uncertainty at a number of steps in the risk assessment scenario tree was high, notably the likelihood that carp become contaminated with the virus and whether effective contact (resulting in pathogen transmission) is made between the introduced carp and susceptible species in England and Wales. The virus would only establish when the water temperature is greater than 12 °C. Analysis of 10 years of data from two rivers in south-west England indicated that establishment could occur over a period of at least 14 weeks a year in southern England (when average water temperature exceed 12 °C). Imports of live fish from Australia need to be evaluated on a case-by-case basis to determine which, if any, sanitary measures are required to reduce the assessed risk to an acceptable level.     

Investigation of risk factors for clinical mastitis in British dairy herds with bulk milk somatic cell counts less than 150,000 cells/ml

A sample of dairy farms in Great Britain with a monthly bulk milk somatic cell count of less than 150,000 cells/ml was enrolled into a 12-month prospective study. At the end of the study, a questionnaire on milking practice and other farm management practices was sent to the 482 farmers who had collected data on the occurrence of mastitis throughout the 12 months. The response rate was 93 per cent. The reported mean incidence of clinical mastitis was 36.9 cases per 100 cow-years. Factors associated with an increase in the incidence of clinical mastitis were cleaning out the straw yard less frequently than every six weeks, more than 5 per cent of cows leaking milk outside the parlour, checking the foremilk, wearing gloves during milking, an average annual milk yield of more than 7000 litres per cow, dipping or spraying teats before milking and keeping milk with a high somatic cell count out of the bulk tank. Factors associated with a decrease in the incidence of clinical mastitis were using a cloth to dry the teats after washing them as part of premilking preparation, using calving boxes for less than 40 per cent of calvings, and using both cubicles and straw yards to house dry cows, as opposed to other housing.     

A framework for understanding the potential for emerging diseases in aquaculture

Numerous diseases have emerged as serious economic or ecological problems in aquaculture species. The combination of factors behind the emergence of each disease is unique, but various common factors are apparent. We combine risk-analysis methods and virulence theory with historical examples (mainly from salmonid production) to identify key disease-emergence risk factors. Diseases have emerged through pathogen exchange with wild populations, evolution from non-pathogenic micro-organisms and anthropogenic transfer of stocks. Aquacultural practices frequently result in high population densities and other stresses (such as intercurrent disease) which increase the risk of infection establishment and spread. As aquaculture expands and new species are farmed, diseases will continue to emerge and affect both wild and farmed fish adversely. The rate and extent of emergence can be reduced by the application of biosecurity programmes designed to mitigate the risk factors for disease emergence.