Sea lice exposure to non-lethal levels of emamectin benzoate after treatments: a potential risk factor for drug resistance

The avermectin derivative emamectin benzoate (EMB) has been widely used by salmon industries around the world to control sea lice infestations. Resistance to this anti-parasitic drug is also commonly reported in these industries. The objective of this study was to quantify the number of sea lice potentially exposed to sub-lethal concentrations of EMB while fish clear the drug after treatments. We assessed juvenile sea lice abundance after 38 EMB treatments on six Atlantic salmon farms, in a small archipelago in British Colombia, Canada, between 2007 and 2018. We fitted a standard EMB pharmacokinetic curve to determine the time when fish treated with this product would have EMB tissue concentrations below the recommended target therapeutic level. During the study, we estimated that for each sea lice treatment there was, on average, an abundance of 0.12 juvenile sea lice per fish during the time period when the concentrations of EMB would have been lower than 60ppb, the recommended therapeutic treatment level for sea lice. The findings from this study on metaphylactic anti-parasitic treatments identify a potential driver for drug resistance in sea lice that should be further explored

La régionalisation des précipitations : une revue bibliographique des développements récents

L'estimation de l'intensité de précipitations extrêmes est un sujet de recherche en pleine expansion. Nous présentons ici une synthèse des travaux de recherche sur l'analyse régionale des précipitations. Les principales étapes de l'analyse régionale revues sont les méthodes d'établissement de régions homogènes, la sélection de fonctions de distributions régionales et l'ajustement des paramètres de ces fonctions.De nombreux travaux sur l'analyse régionale des précipitations s'inspirent de l'approche développée en régionalisation des crues. Les méthodes de types indice de crues ont été utilisées par plusieurs auteurs. Les régions homogènes établies peuvent être contiguës ou non-contiguës. L'analyse multivariée a été utilisée pour déterminer plusieurs régions homogènes au Canada. L'adéquation des sites à l'intérieur d'une région homogène a souvent été validée par une application des L-moments, bien que d'autres tests d'homogénéité aient aussi été utilisés.La loi générale des valeurs extrêmes (GEV) est celle qui a le plus souvent été utilisée dans l'analyse régionale des précipitations. D'autres travaux ont porté sur la loi des valeurs extrêmes à deux composantes (TCEV), de même que sur des applications des séries partielles.Peu de travaux ont porté sur les relations intensité durée dans un contexte régional, ni sur les variations saisonnières des paramètres régionaux. Finalement, les recherches ont débuté sur l'application des concepts d'invariance d'échelle et de loi d'échelle. Ces travaux sont jugés prometteurs.Research on the estimation of extreme precipitation events is currently expanding. This field of research is of great importance in hydraulic engineering not only for the design of dams and dikes, but also for municipal engineering designs. In many cases, local data are scarce. In this context, regionalization methods are very useful tools. This paper summarizes the most recent work on the regionalization of precipitation. Steps normally included in any regionalization work are the delineation of homogenous regions, selection a regional probability distribution function and fitting the parameters.Methods to determine homogenous regions are first reviewed. A great deal of work on precipitation was inspired by methods developed for regional flow analysis, especially the index flood approach. Homogenous regions can be contiguous, but in many cases they are not. The region of influence approach, commonly used in hydrological studies, has not been often applied to precipitation data. Homogenous regions can be established using multivariate statistical approaches such as Principal Component Analysis or Factorial Analysis. These approaches have been used in a number of regions in Canada. Sites within a homogenous region may be tested for their appropriateness by calculating local statistics such as the coefficient of variation, coefficient of skewness and kurtosis, and by comparing these statistics to the regional statistics. Another common approach is the use of L-moments. L-moments are linear combinations of ordered statistics and hence are not as sensitive to outliers as conventional moments. Other homogeneity tests have also been used. They include a Chi-squared test on all regional quantiles associated with a given non-exceedance probability, and a Smirnoff test used to validate the inclusion of a station in the homogenous region.Secondly, we review the distributions and fitting methods used in regionalization of precipitation. The most popular distribution function used is the General Extreme Value (GEV) distribution. This distribution has been recommended for precipitation frequency analysis in the United Kingdom. For regional analysis, the GEV is preferred to the Gumbel distribution, which is often used for site-specific frequency analysis of precipitation extremes. L-moments are also often used to calculate the parameters of the GEV distribution. Some applications of the Two-Component Extreme Value (TCEV) distribution also exist. The TCEV has mostly been used to alleviate the concerns over some of the theoretical and practical restrictions of the GEV.Applications of the Partial Duration Series or Peak-Over-Threshold (POT) approach are also described. In the POT approach, events with a magnitude exceeding a certain threshold are considered in the analysis. The occurrence of such exceedances is modelled as a Poisson process. One of the drawbacks of this method is that it is sometimes necessary to select a relatively high threshold in order to comply with the assumption that observations are independent and identically distributed (i.i.d.). The use of a re-parameterised Generalised Pareto distribution has also been suggested by some researchers.Research on depth-duration relations on a regional scale is also discussed. Empirical approaches used in Canada and elsewhere are described. In most cases, the method consists of establishing a non-linear relationship between a quantile associated with a given duration and its return period to a reference quantile, such as a 1-hour rainfall with a 10-year return period. Depth duration relationships cannot be applied uniformly across Canada for events with durations exceeding two hours. Seasonal variability studies in regionalization are relatively scarce, but are required because of the obvious seasonality of precipitation. In many cases, seasonal regimes may lead to different regionalization approaches for the wet and the dry season. Some research has focused on the use of periodic functions to model regional parameters. Another approach consists of converting the occurrence data of a given event in an angular measurement and developing seasonal indices based on this angular measurement.Other promising avenues of research include the scaling approach. The debate over the possibility of scale invariance for precipitation is ongoing. Simple scaling was studied on a number of precipitation data, but the fact that intermittence is common in precipitation regimes and the presence of numerous zero values in the series does not readily lead to proper application of this approach. Recent research has shown that multiple scaling is likely a more promising avenue

Survey on solar X-ray flares and associated coherent radio emissions

The radio emission during 201 X-ray selected solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zurich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs than the high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron radiation. In 10% of the HXR flares, an intense radiation of the above genuine decimetric types followed in the decay phase or later. Classic meter-wave type III bursts are associated in 33% of all HXR flares, but only in 4% they are the exclusive radio emission. Noise storms were the only radio emission in 5% of the HXR flares, some of them with extended duration. Despite the spatial association (same active region), the noise storm variations are found to be only loosely correlated in time with the X-ray flux. In a surprising 17% of the HXR flares, no coherent radio emission was found in the extremely broad band surveyed. The association but loose correlation between HXR and coherent radio emission is interpreted by multiple reconnection sites connected by common field lines.Comment: Solar Physics, in pres

McGill wetland model: evaluation of a peatland carbon simulator developed for global assessments

We developed the McGill Wetland Model (MWM) based on the general structure of the Peatland Carbon Simulator (PCARS) and the Canadian Terrestrial Ecosystem Model. Three major changes were made to PCARS: (1) the light use efficiency model of photosynthesis was replaced with a biogeochemical description of photosynthesis; (2) the description of autotrophic respiration was changed to be consistent with the formulation of photosynthesis; and (3) the cohort, multilayer soil respiration model was changed to a simple one box peat decomposition model divided into an oxic and anoxic zones by an effective water table, and a one-year residence time litter pool. MWM was then evaluated by comparing its output to the estimates of net ecosystem production (NEP), gross primary production (GPP) and ecosystem respiration (ER) from 8 years of continuous measurements at the Mer Bleue peatland, a raised ombrotrophic bog located in southern Ontario, Canada (index of agreement [dimensionless]: NEP = 0.80, GPP = 0.97, ER = 0.97; systematic RMSE [g C m<sup>−2</sup> d<sup>−1</sup>]: NEP = 0.12, GPP = 0.07, ER = 0.14; unsystematic RMSE: NEP = 0.15, GPP = 0.27, ER = 0.23). Simulated moss NPP approximates what would be expected for a bog peatland, but shrub NPP appears to be underestimated. Sensitivity analysis revealed that the model output did not change greatly due to variations in water table because of offsetting responses in production and respiration, but that even a modest temperature increase could lead to converting the bog from a sink to a source of CO<sub>2</sub>. General weaknesses and further developments of MWM are discussed

McGill Wetland Model: evaluation of a peatland carbon simulator developed for global assessments

International audienceWe developed the McGill Wetland Model (MWM) based on the general structure of the Peatland Carbon Simulator (PCARS) and the Canadian Terrestrial Ecosystem Model. Three major changes were made to PCARS: 1. the light use efficiency model of photosynthesis was replaced with a biogeochemical description of photosynthesis; 2. the description of autotrophic respiration was changed to be consistent with the formulation of photosynthesis; and 3. the cohort, multilayer soil respiration model was changed to a simple one box peat decomposition model divided into an oxic and anoxic zones by an effective water table, and a one-year residence time litter pool. MWM was then evaluated by comparing its output to the estimates of net ecosystem production (NEP), gross primary production (GPP) and ecosystem respiration (ER) from 8 years of continuous measurements at the Mer Bleue peatland, a raised ombrotrophic bog located in southern Ontario, Canada (index of agreement [dimensionless]: NEP=0.80, GPP=0.97, ER=0.97; systematic RMSE [g C m?2 d?1]: NEP=0.12, GPP=0.07, ER=0.14; unsystematic RMSE [g C m?2 d?1]: NEP=0.15, GPP=0.27, ER=0.23). Simulated moss NPP approximates what would be expected for a bog peatland, but shrub NPP appears to be underestimated. Sensitivity analysis revealed that the model output did not change greatly due to variations in water table because of offsetting responses in production and respiration, but that even modest temperature increases could lead to converting the bog from a sink to a source of CO2. General weaknesses and further developments of MWM are discussed

Dengue fever and severe dengue in Barbados, 2008–2016

Analysis of the temporal, seasonal and demographic distribution of dengue virus (DENV) infections in Barbados was conducted using national surveillance data from a total of 3994 confirmed dengue cases. D

A Statistical Survey of Hard X-ray Spectral Characteristics of Solar Flares with Two Footpoints

Using RHESSI data, we have analyzed some 172 hard X-ray peaks during 53 solar flares which exhibited a double-footpoint structure. Fitting both footpoints with power-laws, we find that spectral index differences range mostly between 0 to 0.6, and only rarely go beyond. Asymmetries between footpoints were not observed to be significantly dependent on their mean heliographic position, their relative position with respect to each other, nor their orientation with respect to the solar equator. Assuming a symmetric acceleration process, it is also clear that differences in footpoint spectral indices and footpoint flux ratios can seldom be attributed to a difference in column densities between the two legs of a coronal loop. Our results corroborate better the magnetic mirror trap scenario. Moreover, footpoint asymmetries are more marked during times of peak HXR flux than when averaging over the whole HXR burst, suggesting that the magnetic configuration evolves during individual HXR bursts. We observed also a linear correlation between the peak 50-keV flux and the peak GOES 1-8A channel flux, and that HXR burst duration seem correlated with loop length.Comment: 20 pages, 13 figures. Published in Solar Physic

The RHESSI Microflare Height Distribution

We present the first in-depth statistical survey of flare source heights observed by RHESSI. Flares were found using a flare-finding algorithm designed to search the 6-10 keV count-rate when RHESSI's full sensitivity was available in order to find the smallest events (Christe et al., 2008). Between March 2002 and March 2007, a total of 25,006 events were found. Source locations were determined in the 4-10 keV, 10-15 keV, and 15-30 keV energy ranges for each event. In order to extract the height distribution from the observed projected source positions, a forward-fit model was developed with an assumed source height distribution where height is measured from the photosphere. We find that the best flare height distribution is given by g(h) \propto exp(-h/{\lambda}) where {\lambda} = 6.1\pm0.3 Mm is the scale height. A power-law height distribution with a negative power-law index, {\gamma} = 3.1 \pm 0.1 is also consistent with the data. Interpreted as thermal loop top sources, these heights are compared to loops generated by a potential field model (PFSS). The measured flare heights distribution are found to be much steeper than the potential field loop height distribution which may be a signature of the flare energization process