Comparisons of day-time and night-time hydroacoustic surveys in temperate lakes

In recent years, due to an increased need for non-intrusive sampling techniques, hydroacoustics has attracted attention in fishery science and management. Efforts to promote standardisation are increasing the accuracy, efficiency, and comparability of this method. The European Water Framework Directive and the Standard Operating Procedures for Fisheries Hydroacoustic Surveys in North American Great Lakes has recommended that surveys be conducted at night. At night, fish usually disperse in the water column, thus allowing for single echo detection and subsequent accurate fish size estimation, while day-time schooling behaviour hampers the estimation of fish size. However, sampling during the day would often be safer and cheaper. This study analyses how fisheries hydroacoustic results differ between day-time and night-time surveys, using data from 14 natural temperate lakes of various size. Data collected during the day and night at two depth layers linked to thermal stratification were compared in terms of acoustic scattering strength, target strength, and biomass estimates. The results showed a significant correlation between day-time and night-time estimates, though biomass in the upper layer was biased for day-time surveys, mainly due to incorrect fish size estimates resulting from rare single echo detections and schooling behaviour. Biomass estimates for the lower depth layer did not significantly differ between the two diel periods. Thus, this study confirms that hydroacoustic sampling in temperate lakes should be performed at night for accurate fish stock biomass estimates

Synchrony in whitefish stock dynamics: disentangling the effects of local drivers and climate

Synchronic variations in abundance in populations of the same species are common phenomena encountered in various environments, including lakes, and different taxa of freshwater fishes. This phenomenon can be caused by similar environmental conditions across physically separated populations. In the context of the ongoing climate change, it is essential to test this hypothesis, identify the factors driving the synchrony and elucidate the mechanisms, in the attempt to improve fisheries management. This study investigates synchronic variations in European whitefish (Coregonus spp.) populations in five peri-alpine lakes. The hypothesis suggests that shared biotic or abiotic factors contribute to similar trends in whitefish landings. Environmental and seasonal variables impacting the early life stages of the species were analyzed, and the Euclidean distances between the multivariate time series were calculated to identify similarities or dissimilarities in lake environmental parameters. We found that regional winter and spring temperatures were consistent across the lakes, but these factors did not fully account for variations in landings statistics. Wind intensity, water level and zooplankton abundance showed lake-specific patterns that could better explain local conditions and dynamics. Linear models did not reveal a coherent correlation with a common environmental variable across all lakes. However, distinct relationships were found in four of the lakes, with local factors significantly contributing to abundance variations. The spring abundance of Daphnia spp., a primary food source for whitefish larvae, was the main factor correlated with fish landing trends in Lake Geneva and Lake Bourget. Higher availability of Daphnia spp. may decrease intraspecific competition and density-dependent mortality. In Lake Neuchâtel, winter water temperature was negatively correlated with fish abundance proxies, suggesting that warmer winters may compromise reproduction success. Lake Annecy saw an increase in whitefish landings following a substantial reduction in fishing efforts during the late 2000s. A significant negative correlation was found between whitefish landings and fishing efforts. No relationship was found for Lake Aiguebelette, maybe due to a lack of zooplankton data. In conclusion, the observed synchrony in the European whitefish population is likely driven by a combination of interacting environmental and anthropogenic factors rather than a single common variable. Further research and a more detailed dataset are needed to better understand these complex relationships.   Article cover image: Whitefish (Credit: Rémi Masson

Comparison of single- and multi-trait approaches to identify best wild candidates for aquaculture shows that the simple way fails

International audiencein agriculture, diversifying production implies picking up, in the wild biodiversity, species or populations that can be domesticated and fruitfully produced. two alternative approaches are available to highlight wild candidate(s) with high suitability for aquaculture: the single-trait (i.e. considering a single phenotypic trait and, thus, a single biological function) and multi-trait (i.e. considering multiple phenotypic traits involved in several biological functions) approaches. Although the former is the traditional and the simplest method, the latter could be theoretically more efficient. However, an explicit comparison of advantages and pitfalls between these approaches is lacking to date in aquaculture. Here, we compared the two approaches to identify best candidate(s) between four wild allopatric populations of Perca fluviatilis in standardised aquaculture conditions. our results showed that the single-trait approach can (1) miss key divergences between populations and (2) highlight different best candidate(s) depending on the trait considered. In contrast, the multi-trait approach allowed identifying the population with the highest domestication potential thanks to several congruent lines of evidence. nevertheless, such an integrative assessment is achieved with a far more time-consuming and expensive study. therefore, improvements and rationalisations will be needed to make the multi-trait approach a promising way in the aquaculture development

Warming winters threaten peripheral Arctic charr populations of Europe

As the global climate warms, the fate of lacustrine fish is of huge concern, especially given their sensitivity as ectotherms to changes in water temperature. The Arctic charr (Salvelinus alpinus L.) is a salmonid with a Holarctic distribution, with peripheral populations persisting at temperate latitudes, where it is found only in sufficiently cold, deep lakes. Thus, warmer temperatures in these habitats particularly during early life stages could have catastrophic consequences on population dynamics. Here, we combined lake temperature observations, a 1-D hydrodynamic model, and a multi-decadal climate reanalysis to show coherence in warming winter water temperatures in four European charr lakes near the southernmost limit of the species’ distribution. Current maximum and mean winter temperatures are on average ~ 1 °C warmer compared to early the 1980s, and temperatures of 8.5 °C, adverse for high charr egg survival, have frequently been exceeded in recent winters. Simulations of winter lake temperatures toward century-end showed that these warming trends will continue, with further increases of 3–4 °C projected. An additional 324 total accumulated degree-days during winter is projected on average across lakes, which could impair egg quality and viability. We suggest that the perpetuating winter warming trends shown here will imperil the future status of these lakes as charr refugia and generally do not augur well for the fate of coldwater-adapted lake fish in a warming climate

Metadata standards and practical guidelines for specimen and DNA curation when building barcode reference libraries for aquatic life

DNA barcoding and metabarcoding is increasingly used to effectively and precisely assess and monitor biodiversity in aquatic ecosystems. As these methods rely on data availability and quality of barcode reference libraries, it is important to develop and follow best practices to ensure optimal quality and traceability of the metadata associated with the reference barcodes used for identification. Sufficient metadata, as well as vouchers, corresponding to each reference barcode must be available to ensure reliable barcode library curation and, thereby, provide trustworthy baselines for downstream molecular species identification. This document (1) specifies the data and metadata required to ensure the relevance, the accessibility and traceability of DNA barcodes and (2) specifies the recommendations for DNA harvesting and for the storage of both voucher specimens/samples and barcode data.info:eu-repo/semantics/publishedVersio

Hydro-acoustique et réservoirs : Validation d’un drone hydroacoustique en réservoir et discrimination de cibles par approche large bande

L’hydro-acoustique est devenue une méthode incontournable de l’évaluation des populations de poissons dans les écosystèmes lacustres et de la description de leurs relations avec l’écosystème. Cette méthode, non intrusive, fait désormais partie intégrante des procédures d’échantillonnage des peuplements de poissons recommandés par la DCE et a fait l’objet d’une normalisation par le Comité Européen de Normalisation (CEN EN 1590). À l’heure où l’utilisation de ces méthodes s’intensifie, le nouveau défi est leur utilisation de façon autonome afin de pouvoir acquérir plus de données aussi bien spatialement que temporellement. De plus, la nouvelle génération de sondeur type large bande récemment commercialisée permettra de mieux prendre en compte les réponses fréquentielles des cibles pour aborder la discrimination spécifique ou mieux décrire les écosystèmes en limitant par exemple les confusions possibles entre bancs de poissons et arbres immergés. Un engin autonome, le HARLE (Hydroacoustic Autonomous boat for Remote fish detections in LakE) équipé d’un sondeur EK80 (120 kHz) émettant en position verticale, a été développé par l’INRAE en partenariat avec CT2MC. La première version a été validée en lac naturel et la version 2.0 adaptée aux réservoirs nécessite d’être validée

Interprétation de l’âge à partir des écailles sur des espèces de salmonidés lacustres, le corégone (Coregonus sp.) et l’omble chevalier (Salvelinus alpinus)

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In situ TS detections using two generations of echo-sounder, EK60 and EK80: the continuity of fishery acoustic data in lakes

International audienceUtilisée depuis plusieurs décennies et reconnue aujourd'hui comme une méthode fiable, l'acoustique halieutique est couramment utilisée dans les études scientifiques et les campagnes de suivi. En Europe, au cours des dernières décennies, l'échosondeur scientifique le plus fréquemment utilisé a été le EK60 de la société Simrad (Simrad Kongsberg Maritime AS, Horten, Norvège). Un nouveau modèle d'échosondeur, le EK80, a été développé récemment, et il faut donc vérifier si les résultats obtenus par les deux générations d'échosondeur (EK60 et EK80) donnent les mêmes résultats. Ceci est d'une importance capitale dans le contexte des séries chronologiques. Des travaux récents ont déjà abordé cette comparaison, en s'intéressant à S A(coefficient de rétrodiffusion de la zone nautique) mais la fiabilité des systèmes à mesurer avec précision la force de la cible (TS, en dB) n'a été testée qu'à l'aide de sphères d'étalonnage. Notre travail vise à tester l'hypothèse selon laquelle, à une fréquence donnée, les TS enregistrés simultanément in situpar un EK60 et un EK80, en mode CW, n'étaient pas statistiquement différents. Les données ont été enregistrées dans deux lacs périalpins en utilisant les deux systèmes échantillonnant séquentiellement un volume similaire. À l'aide de tests statistiques, les métriques acoustiques ont été comparées. Pour le TS, des différences statistiquement significatives ont été trouvées entre les deux générations d'échosondeur. Cependant, ces différences n'étaient pas assez importantes pour affecter la densité de poissons utilisée pour la gestion de la pêche ou les recherches sur la population de poissons. La continuité des séries temporelles acquises avec l'EK60 est assurée lorsque l'on passe à l'échosondeur EK80 pour la recherche et le suivi des écosystèmes lacustres

Hydroacoustiques et réservoirs Validation d'un drone hydroacoustique en réservoir et discrimination de cibles par approche large bande

L’hydro-acoustique est devenue une méthode incontournable de l’évaluation des populations de poissons dans les écosystèmes lacustres et de la description de leurs relations avec l’écosystème. Cette méthode, non intrusive, fait désormais partie intégrante des procédures d’échantillonnage des peuplements de poissons recommandés par la DCE et a fait l’objet d’une normalisation par le Comité Européen de Normalisation (CEN EN 1590). À l’heure où l’utilisation de ces méthodes s’intensifie, le nouveau défi est leur utilisation de façon autonome afin de pouvoir acquérir plus de données aussi bien spatialement que temporellement. De plus, la nouvelle génération de sondeur type large bande récemment commercialisée permettra de mieux prendre en compte les réponses fréquentielles des cibles pour aborder la discrimination spécifique ou mieux décrire les écosystèmes en limitant par exemple les confusions possibles entre bancs de poissons et arbres immergés. Un engin autonome, le HARLE (Hydroacoustic Autonomous boat for Remote fish detections in LakE) équipé d’un sondeur EK80 (120 kHz) émettant en position verticale, a été développé par l’INRAE en partenariat avec CT2MC. La première version a été validée en lac naturel et la version 2.0 adaptée aux réservoirs nécessite d’être validée