Dynamic competition and resource partitioning during the early life of two widespread, abundant and ecologically similar fishes

Competition and resource partitioning can have profound implications for individuals, populations and communities, and thus food webs, ecosystems and the management of biota and environments. In many species, the impacts of competition and resource partitioning are believed to be most severe during early life, but our understanding of the mechanisms and implications is incomplete. This study revealed short-term variations in both the occurrence and direction of competition during the early life of roach Rutilus rutilus and common bream Abramis brama, two of the most widespread and abundant fish species in Europe. There was also evidence of resource partitioning when small taxa dominated the zooplankton, but not when larger taxa were more abundant. In spite of the differences in foraging ecology, there were no significant differences in growth or nutritional condition in allopatry and sympatry. Similar to the concept of condition-specific competition, when competitive abilities vary along environmental gradients, the impacts of interspecific interactions on foraging ecology, growth and condition are dynamic and likely vary according to temporal fluctuations in prey availability. This is important because short-term incidences of competition could have cascading effects on food webs, even when no impacts on growth rates or condition are detected

Mapping habitat indices across river networks using spatial statistical modelling of River Habitat Survey data

Freshwater ecosystems are declining faster than their terrestrial and marine counterparts because of physical pressures on habitats. European legislation requires member states to achieve ecological targets through the effective management of freshwater habitats. Maps of habitats across river networks would help diagnose environmental problems and plan for the delivery of improvement work. Existing habitat mapping methods are generally time consuming, require experts and are expensive to implement. Surveys based on sampling are cheaper but provide patchy representations of habitat distribution. In this study, we present a method for mapping habitat indices across networks using semi-quantitative data and a geostatistical technique called regression kriging. The method consists of the derivation of habitat indices using multivariate statistical techniques that are regressed on map-based covariates such as altitude, slope and geology. Regression kriging combines the Generalised Least Squares (GLS) regression technique with a spatial analysis of model residuals. Predictions from the GLS model are ‘corrected’ using weighted averages of model residuals following an analysis of spatial correlation. The method was applied to channel substrate data from the River Habitat Survey in Great Britain. A Channel Substrate Index (CSI) was derived using Correspondence Analysis and predicted using regression kriging. The model explained 74% of the main sample variability and 64% in a test sample. The model was applied to the English and Welsh river network and a map of CSI was produced. The proposed approach demonstrates how existing national monitoring data and geostatistical techniques can be used to produce continuous maps of habitat indices at the national scale

Read counts from environmental DNA (eDNA) metabarcoding reflect fish abundance and biomass in drained ponds.

The sampling of environmental DNA (eDNA) coupled with cost-efficient and ever-advancing sequencing technology is propelling changes in biodiversity monitoring within aquatic ecosystems. Despite the increasing number of eDNA metabarcoding approaches, the ability to quantify species biomass and abundance in natural systems is still not fully understood. Previous studies have shown positive but sometimes weak correlations between abundance estimates from eDNA metabarcoding data and from conventional capture methods. As both methods have independent biases a lack of concordance is difficult to interpret. Here we tested whether read counts from eDNA metabarcoding provide accurate quantitative estimates of the absolute abundance of fish in holding ponds with known fish biomass and number of individuals. Environmental DNA samples were collected from two fishery ponds with high fish density and broad species diversity. In one pond, two different DNA capture strategies (on-site filtration with enclosed filters and three different preservation buffers versus lab filtration using open filters) were used to evaluate their performance in relation to fish community composition and biomass/abundance estimates. Fish species read counts were significantly correlated with both biomass and abundance, and this result, together with information on fish diversity, was repeatable when open or enclosed filters with different preservation buffers were used. This research demonstrates that eDNA metabarcoding provides accurate qualitative and quantitative information on fish communities in small ponds, and results are consistent between different methods of DNA capture. This method flexibility will be beneficial for future eDNA-based fish monitoring and their integration into fisheries management

Water Framework Directive Intercalibration: Central-Baltic Lake Fish fauna ecological assessment methods

The European Water Framework Directive (WFD) requires the national classifications of good ecological status to be harmonised through an intercalibration exercise. In this exercise, significant differences in status classification among Member States are harmonized by comparing and, if necessary, adjusting the good status boundaries of the national assessment methods. Intercalibration is performed for rivers, lakes, coastal and transitional waters, focusing on selected types of water bodies (intercalibration types), anthropogenic pressures and Biological Quality Elements. Intercalibration exercises are carried out in Geographical Intercalibration Groups - larger geographical units including Member States with similar water body types - and followed the procedure described in the WFD Common Implementation Strategy Guidance document on the intercalibration process (European Commission, 2011). The Technical report on the Water Framework Directive intercalibration describes in detail how the intercalibration exercise has been carried out for the water categories and biological quality elements. The Technical report is organized in volumes according to the water category (rivers, lakes, coastal and transitional waters), Biological Quality Element and Geographical Intercalibration group. This volume addresses the intercalibration of the Lake Central-Baltic Fish ecological assessment methods. Part A: This document comprises an overview and detailed descriptions of fish-based lake ecological assessment methods. Part B describes the construction of multiple pressure index in the Central-Baltic region. Part C describes the procedure and results of the boundary harmonisation of national fish-based lake assessment systemsJRC.D.2-Water and Marine Resource

Intercalibration of the national classifications of ecological status for Central-Baltic Lakes: Biological Quality Element: Fish fauna: Part B and C

The European Water Framework Directive (WFD) requires the national classifications of good ecological status to be harmonised through an intercalibration exercise. In this exercise, significant differences in status classification among Member States are harmonized by comparing and, if necessary, adjusting the good status boundaries of the national assessment methods. Intercalibration is performed for rivers, lakes, coastal and transitional waters, focusing on selected types of water bodies (intercalibration types), anthropogenic pressures and Biological Quality Elements. Intercalibration exercises are carried out in Geographical Intercalibration Groups - larger geographical units including Member States with similar water body types - and followed the procedure described in the WFD Common Implementation Strategy Guidance document on the intercalibration process (European Commission, 2011). The Technical report on the Water Framework Directive intercalibration describes in detail how the intercalibration exercise has been carried out for the water categories and biological quality elements. The Technical report is organized in volumes according to the water category (rivers, lakes, coastal and transitional waters), Biological Quality Element and Geographical Intercalibration group. This volume addresses the intercalibration of the Lake Central-Baltic Fish ecological assessment methods. This volume on intercalibration of the Lake Central Baltic Fish ecological assessment methods is split into three parts: Part A, a document that provides an overview and detailed descriptions of fish-based lake ecological assessment methods. Parts B and C: This document comprises two Parts, B and C. Part B describes the construction of multiple pressure index in the Central-Baltic region. Part C describes the procedure and results of the boundary harmonisation of national fish-based lake assessment systems.  JRC.D.2-Water and Marine Resource

Evaluation of horizontally and vertically aligned bar racks for guiding downstream moving juvenile chub (Squalius cephalus) and barbel (Barbus barbus)

Highlights• Horizontally and vertically oriented bar racks were evaluated for fish screening • Downstream movements of groups of chub and barbel were recorded and analysed• Sweeping flows across the rack face to the bypass were not established • Consequently, total guidance was low for both species under all treatments• The bar racks used were not suitable for fish guidance under the tested conditionsAbstractBar racks are commonly installed to divert fish away from water intakes, such as those at hydropower stations or other abstraction points. In temperate regions their effectiveness has predominantly been assessed in relation to diadromous species, such as salmon and eel. This study compared the efficacy of horizontally and vertically oriented racks (5 mm diameter and 10 mm spacing) to guide downstream moving groups of five chub (Squalius cephalus) and barbel (Barbus barbus) to a bypass channel in a recirculating flume under two discharge regimes, and with the rack angled at either 30° or 45° to the direction of flow. Regardless of treatment, the bulk flow predominantly passed through the bars resulting in a lack of a well-established sweeping flow across the rack face, and consequently many instances of entrainment and impingement occurred. Total guidance (the number of bypass entries expressed as a percentage of the total number of approaches) was low and comparable between species with means of 21.3% and 24.8% for chub and barbel, respectively. Bar orientation had limited influence on all metrics, with the exception of the number of guidance events which was higher for the vertical treatment. Interspecific differences in the number of entrainments and guidance events and the exhibition of fine-scale avoidance behaviours were apparent, being higher for chub. In conclusion, the racks used here were not suitable for guiding juvenile cyprinids under conditions similar to those tested. Accounting for interspecific differences and reducing avoidance behaviour are important factors that should be considered in advancing guidance screens for multiple species. Keywords: Avoidance, Bar racks, Cyprinidae, Fish passage, Guidance <br/

Dataset for Evaluation of horizontally and vertically aligned bar racks for guiding downstream moving juvenile chub (Squalius cephalus) and barbel (Barbus barbus)

Data supports the paper &#39;Evaluation of horizontally and vertically aligned bar racks for guiding downstream moving juvenile chub (Squalius cephalus) and barbel (Barbus barbus)&#39; in Ecological Engineering.</span

Effectiveness of horizontally and vertically oriented wedge-wire screens to guide downstream moving juvenile chub (Squalius cephalus)

Physical screens are commonly installed to prevent downstream moving fish from entering dangerous areas (e.g. intakes to hydropower turbines, irrigation canals, and fish farms), and divert them to preferred alternative routes (e.g. bypass systems). In northern temperate regions, assessments of the functioning of screens have largely focused on diadromous species (e.g. salmon and eel), while ignoring those with other life history characteristics. Recent developments in physical screens include the usage of horizontally aligned bars as opposed to traditional vertical ones, but a direct comparison in terms of guidance remains untested. To address this and aid in the development of successful screens for the wider fish community, this study compared the efficacy of wedge-wire screens with horizontally and vertically oriented bars to block and divert downstream moving groups of five chub (Squalius cephalus) to a bypass channel installed in a recirculating flume under two discharge regimes. Hydrodynamics differed between horizontal and vertical screens under both flows; the vertical configuration created a higher velocity gradient towards the bypass. Total guidance (the number of bypass entries as a percentage of the number of approaches) was generally low (mean = 17.3% for all treatments), the highest being recorded for the horizontal screen under low discharge (25.3%). Rejections and holding station events, both proxies for fish exhibiting avoidance of the hydrodynamic conditions created by the screen, were lowest under this treatment. Horizontal performed better than vertical screens in guiding fish to the bypass under low but not high discharge. The results confirm that screen functioning is dependent on hydrodynamic conditions as well as the fish's behavioural response.</p

Use of acoustics to enhance the efficiency of physical screens designed to protect downstream moving European eel (Anguilla anguilla)

European eel (Anguilla anguilla) are vulnerable to entrainment at a variety of man-made intakes, including those that lead to hydropower turbines or other abstraction points. Two experiments were conducted to investigate the potential for acoustic stimuli to improve the efficiency of a vertical bar-screen to guide downstream moving eel. Three underwater speakers were installed along the channel wall of an external flume, upstream of the screen. In first experiment (1), screen guidance efficiency recorded in the presence (treatment) and absence (control) of a continuous broadband stimulus was individually compared between fish from to respective groups. Adopting a “before-after” design, the second experiment (2) assessed individually the guidance of control eel from the group previously used in experiment 1 when exposed to a 100 Hz pulse. The majority of eel reached the bypass in both experiments with only three passing through the screen during the controls against one during each acoustic treatment. Rejection of the area adjacent to the speakers was more common during the acoustic treatment with eel moving past the speakers more rapidly in the presence of sound. The results suggest that employing acoustic stimuli enhances the guidance efficiency of physical screens