Evaluating the impact of hydropower on downstream migrating anguillid eels: Catchment-wide and fine-scale approaches to identify cost-effective solutions

Hydropower is an increasingly popular source of renewable and ‘green’ (in terms of emissions) energy, but reduced longitudinal connectivity and diverting flow through turbines can have negative impacts on catadromous anguillid eel species that have declined globally. There is an urgent need for environmental managers to perform remediation actions, such as protecting flows for migratory fish and providing passage solutions at infrastructure, under increasing legislative pressure. To deliver this, a more comprehensive understanding of eel migration in catchments with hydropower is required. Here, we illustrate the importance of catchment-wide and fine-scale acoustic telemetry, coupled with the influence of eel maturation (i.e. sex steroid levels), to determine the impact of Wairua run-of-river Power Station (WPS) on downstream migrating shortfin eels (Anguilla australis; n = 25) in Wairua River, New Zealand. Migration speed through the unregulated reach upstream of WPS was positively correlated with flow, but not eel length or sex steroids. Three eels passed a diversion weir (DW) to follow the natural watercourse and eight entered the WPS canal. Eels predominantly entered (95.2%) and were last detected (85.7%) in WPS forebay during hours of darkness. Eleven (52%) of the 21 eels that entered WPS forebay were impinged or entrained, all when three or four turbines were in operation (power generation >3.04 MW). Ten (48%) passed WPS spillway during significantly higher spill than impinged or entrained eels, with four passing during no turbine operation, after experiencing high flows near the intake (multiple receivers in WPS forebay used to quantify fine-scale behaviour). On average, eels were impinged or entrained at WPS significantly quicker (6.40 ± 11.13 days) than eels that entered the spillway (25.17 ± 15.12 days), but eel length and sex steroids did not significantly influence fate. Of the eels that migrated through the entire 55 km study reach, passage time at DW and WPS equated to 0.01–0.02% and 47.62–92.17% of their migration, respectively. Mitigation for WPS (and similar power schemes) should focus on operational or physical changes at DW to minimise eels entering power station forebay(s). Turbine shutdowns, ensuring WPS spillway is available and the provision of a bypass channel in WPS forebay are also discussed as ways to conserve the species with the potential to save costs for water resource managers

Response to Selection for a High or a Low Sex Ratio in Wolbachia-infected Lines of Trichogramma cordubensis Subjected to High Temperature

Trichogramma cordubensis is an egg parasitoid completely infected by endosymbiotic bacteria belonging to the Wolbachia genus and inducing the thelytokous mode of reproduction. Previous results showed that the thelytoky persistence at high temperature is genetically variable. Experimental selection was performed to confirm these results and to determine the possibilities of adaptation to the environment assuming cyclic bisexual reproduction. No selection was efficient and the genetic variability of the sex ratio at high temperature is probably lower than previously assumed. This reduces the adaptive possibilities in the studied Trichogramma species.Установлено, что Trichogramma cordubensis - яйцевой паразит, характеризующийся наличием эндосимбионтных бактерий Wolbachia и телитокическим способом размножения. Отмечено, что устойчивость к высокой температуре у телитокических видов генетически варьирует. Проведена экспериментальная селекция линий с высоким и низким половым индексом для определения возможных адаптаций к условиям окружающей среды, вызывающим двуполый способ размножения. Установлено, что селекция выбранных линий была не эффективной. Генетически обусловленная изменчивость полового индекса при высокой температуре оказалась ниже, чем предполагалось. Отмечено, что это уменьшает адаптивные возможности T. cordubensis

Establishment of self-sustaining populations of non-native fish species in the River Trent and Warwickshire Avon, UK, indicated by the presence of 0+ fish

This study investigated the reproduction of non-native fish species, inferred from the presence of 0+ fish, in three English lowland rivers over an 8 year period. Evidence of self-sustaining populations was found for three non-native fish species, namely zander Sander lucioperca (in the River Trent and Warwickshire Avon), bitterling Rhodeus amarus (in the Trent) and carp Cyprinus carpio (in the Trent and Avon). Notwithstanding, such fishes are currently rare, accounting for < 1% of the 0+ fish communities of these two rivers, and no non-native species were recorded from the Yorkshire Ouse. It is possible, however, that improvements in water quality and habitat, together with the potential effects of climate change, may facilitate consolidation and expansion of their populations, as well as those of other non-native fish species already present or introduced in the future. This could have repercussions for the ecology and management of non-native fishes in the UK. © 2007 The Author(s)

Temporal and spatial variations in the abundance and population structure of the spined loach (Cobitis taenia), a scarce fish species: implications for condition assessment and conservation

Effective conservation of protected species requires accurate estimates of the status of their populations. In the UK, this led to the production of a series of sampling protocols to establish the status of designated species against predetermined conservation objectives: a process known as 'condition assessment'. Condition assessments involve comparisons of various parameters, invariably including abundance and/or population structure, of the target species against criteria that are judged to be indicative of viable populations.This study investigated temporal and spatial variations in the abundance and population structure of spined loach (Cobitis taenia), a scarce species indigenous to Europe and central Asia. Specifically, the study compared the density, number of age classes and percentage contribution of the 0+ year age class of spined loach between day and night, months, years and locations.There were marked diel, seasonal, annual and spatial variations in the density, number of age classes and percentage contribution of 0+ year spined loach. Such phenomena are important because monitoring programmes conducted at inappropriate times of day or year, or with insufficient frequency or geographical coverage, could lead to inaccurate assessments of the condition of protected populations and, consequently, to inadequate conservation measures. Notwithstanding, there were few impacts on the condition assessments of the spined loach populations because at least one of the parameters invariably failed to satisfy the population condition assessment criteria.A prerequisite for successful conservation is an effective monitoring programme. It is therefore essential that surveys to assess the condition of populations of protected species are designed with due consideration of their diel behaviour, breeding season, life span and habitat use. It is recommended that the monitoring protocol and condition assessment criteria for spined loach are amended, and that surveys are conducted by trawling, in late summer, at least every 3-4years

The impact of partially missing communities~on the reliability of centrality measures

Network data is usually not error-free, and the absence of some nodes is a very common type of measurement error. Studies have shown that the reliability of centrality measures is severely affected by missing nodes. This paper investigates the reliability of centrality measures when missing nodes are likely to belong to the same community. We study the behavior of five commonly used centrality measures in uniform and scale-free networks in various error scenarios. We find that centrality measures are generally more reliable when missing nodes are likely to belong to the same community than in cases in which nodes are missing uniformly at random. In scale-free networks, the betweenness centrality becomes, however, less reliable when missing nodes are more likely to belong to the same community. Moreover, centrality measures in scale-free networks are more reliable in networks with stronger community structure. In contrast, we do not observe this effect for uniform networks. Our observations suggest that the impact of missing nodes on the reliability of centrality measures might not be as severe as the literature suggests

Novel insights into the marine phase and river fidelity of anadromous twaite shad Alosa fallax in the UK and Ireland

© 2020 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons Ltd Most research on anadromous fishes has been invested in their freshwater life-phases, resulting in a relatively sparse understanding of their spatial ecology during marine life-phases. However, understanding the marine dispersal of anadromous fishes is essential to identify threats and to implement conservation measures that fully encompass their lifecycle. The twaite shad Alosa fallax is an anadromous fish increasingly imperilled across its range due to pollution, harvesting, and impediments to freshwater migration, but little is known about its distribution and movements during its marine life-phase. Here, the application of acoustic telemetry provided novel insights into the coastal dispersal of twaite shad in the UK and Ireland during 2018–2019, and the freshwater entry of individuals during the 2019 spawning season. Of 73 twaite shad acoustic-tagged during their upstream migration in the River Severn in May 2018, 58 emigrated from the river. Twelve were subsequently detected 200 km to the south-west at the Taw–Torridge Estuary between July 2018 and April 2019, where estuarine movements up to 5.8 km inland occurred in summer, winter, and spring. One was subsequently detected in the Munster Blackwater Estuary (Ireland) and then in the River Severn, indicating a minimum movement distance of 950 km. Thirty-four (59%) of the emigrating individuals from 2018 re-entered fresh water in the rivers Severn (n = 33) and Wye (n = 2) in April and May 2019. These results suggest year-round use of estuarine and nearshore habitats by at least a subset of the twaite shad population during their marine phase, providing evidence of potential range overlap between populations that spawn in different areas in the UK and Ireland, which may be facilitated by substantial dispersal. The results also highlight the potential of telemetry for estimating freshwater and marine mortality, and the benefits of sharing detection data across networks

The Response of River-Resident Fish to Reservoir Freshet Releases of Varying Profiles Intended to Facilitate a Spawning Migration

Natural hydrological regimes encompass varying seasonal flow characteristics that provide fish with cues and opportunities for upstream spawning migrations, but these flows are often modified/absent in regulated rivers. Compensatory artificial flows (freshets) can be released from reservoirs to replicate these characteristics, but studies testing their effectiveness are limited. To address this, river‐resident brown trout, a species known to undertake spawning migrations, were manually tracked using radio telemetry in a regulated upland river in northern England in response to 11 freshet releases of differing timing, magnitude and duration. Spawning migrations were not observed because extent of movement during freshets was generally small and the pattern of movement (i.e. directionality and relocation indices) was comparable between impact/control reaches. Movements during freshets were comparable with those observed the days immediately before/after and were small relative to the entire tracking period. In conclusion, freshets characteristic of those recommended to produce “naturalized” autumn/winter flow elevations did not stimulate/facilitate spawning migrations of river‐resident brown trout under the given seasonal conditions. Outside freshets, longer unidirectional movements occurred during low flow periods and elevated river level due to rainfall, including during periods of reservoir overtopping. Notwithstanding, fish in experimental reaches were significantly more active (total distance moved) and occupied a larger extent of river (range during freshet) than those in control reaches during short‐duration freshets. Therefore, during dry years/when (autumn/winter) reservoir overtopping events are unlikely, small‐magnitude freshets providing flows that allow fish short opportunities to search for/find superior local habitat whilst minimising total water released are recommended

Overcoming the dichotomy of implementing societal flood risk management while conserving instream fish habitat – A long-term study from a highly modified urban river

Flood Risk Management (FRM) is often essential to reduce the risk of flooding to properties and infrastructure in urban landscapes, but typically degrades the habitats required by many aquatic animals for foraging, refuge and reproduction. This conflict between flood risk management and biodiversity is driven by conflicting directives, such as the EU Floods and Water Framework Directives, and has led to a requirement for synergistic solutions for FRM that integrate river restoration actions. Unfortunately, ecological monitoring and appraisal of combined FRM and river restoration works is inadequate. This paper uses a case study from the River Don in Northern England to evaluate the effects of the FRM and subsequent river restoration works on instream habitat and the associated fish assemblage over an 8-year period. Flood risk management created a homogeneous channel but did not negatively affect fish species composition or densities, specifically brown trout. Densities of adult brown trout were comparable pre and post-FRM, while densities of juvenile bullhead and brown trout increased dramatically post FRM. River restoration works created a heterogeneous channel but did not significantly improve species composition or brown trout density. Species composition post-river restoration works returned to that similar to pre-FRM over a short-term period, but with improved numbers of juvenile bullhead. Although habitat complexity increased after river restoration works, long-term changes in species composition and densities were marginal, probably because the river reset habitat complexity within the time framework of the study

Comparison of Wolbachia Bacterial Density in Females of Four Thelythokous Strains of Trichogramma cordubensis and T. evanescens (Hymenoptera, Trichogrammatidae)

The endosymbionts of the genus Wolbachia infect numerous arthropods and nematods, and often cause different effects on the reproduction of these hosts. The endosymbiotic bacteria Wolbachia induces the thelytokous mode of reproduction in the egg parasitoids of the genus Trichogramma. The Dot-blot technique was performed to compare the symbiont Wolbachia density using the wsp gene of Wolbachia and the 18S gene of Trichogramma. It was established that Wolbachia density is not different in two host species, Trichogramma cordubensis Vargas et Cabello and T. evanescens Haliday.Эндосимбиотические бактерии рода Wolbachia заражают различных артропод и нематод, оказывая различный эффект на их репродуктивные особенности. Бактерии рода Wolbachia вызывают телитокию у яйцеедов рода Trichogramma. Использована техника Dot-blot для сравнения плотности симбионта Wolbachia, с помощью выделения гена wsp у симбионта Wolbachia и гена 18S у Trichogramma. Экспериментально установлено, что плотность Wolbachia у двух видов, Trichogramma cordubensis Vargas et Cabello и T. evanescens Haliday, одинаковая