Search

Uncrewed surface vehicles (USVs) equipped with echosounders have the potential to replace or enhance acoustic observations from conventional research vessels (RVs), increase spatial and temporal coverage, and reduce cost and carbon emission. We discuss the objectives, system requirements, infrastructure, and regulations for using USVs with echosounders to conduct ecological experiments, acoustic-trawl surveys, and long-term monitoring. We present four example applications of USVs with lengths <8 m, and highlight some advantages and disadvantages relative to RV-based data acquisitions. Sail-driven USVs operate continuously for months and are more mature than motorized USVs, but they are slower. To maintain the pace of an RV, multiple sail-powered USVs sample in coordination. In comparison, motorized USVs can travel as fast as RVs and therefore may facilitate a combined survey, interleaving USV and RV transects, with RV-based biological sampling. Important considerations for all USVs include platform design, noise and transducer motion mitigation, communications and operations infrastructure, onboard data processing, biological sampling approach, and legal requirements. This technology is evolving and applied in multiple disciplines, but further development and institutional commitment are needed to allow USVs equipped with echosounders to become ubiquitous and useful components of a worldwide network of autonomous ocean observation platforms. [ABSTRACT FROM AUTHOR]

Broadband frequency-modulated signals are believed to improve acoustic spectral-based target classification. Efficient use of uncrewed surface vehicles (USV) for fisheries science applications, with no possibility for biological sampling, is believed to be facilitated by use of broadband signals with methods for target classification. If the broadband frequency response used to train automated target classifiers are obtained from conventional research vessels (RVs), due to potential vessel avoidance, the swimming angle distribution may be different than for USVs. This may have consequences for target classification if the model is trained with RV data. The aim of this study was to assess whether the frequency response differs between platforms due to avoidance. Broadband acoustic data were collected with a conventional RV and a small USV. The broadband frequency response of Norwegian spring spawning herring obtained with the USV and RV was found to be significantly different for shallow herring layers in the 200 kHz band. This indicates that broadband frequency response has potential as a tool for real-time monitoring of behaviour reactions to vessels and to provide insight into fish behaviour in general. When using broadband frequency response for target classification, the potential platform-dependent broadband frequency response should be considered. [ABSTRACT FROM AUTHOR]

For many aquatic animals, distributional patterns, trophodynamic relationships, and reproductive activity are driven by complex biotic and abiotic ecosystem interactions that influence behaviour. Linking behavioural information to environmental stimuli and stressors can, therefore, help to anticipate population and ecosystem responses to changing conditions and inform management. However, behavioural information is challenging to obtain because many sampling gears do not provide adequate spatial or temporal resolution, or potentially alter behaviours. Traditionally, most behavioural studies have been laboratory experiments, while behaviour in situ has often been inferred indirectly. Advancements in imaging sonar technology enable the study of in situ behaviours with the potential to address many understudied relationships. In this review we discuss applications of imaging sonar among a meta-analysis of 155 studies of aquatic organisms in their environments. We evaluate the performance of imaging sonar for studying inter- and intra-specific interactions, associations with complex and sensitive habitats and low-visibility environments, and to evaluate traditional fisheries sampling gears. We examine the data processing and analytical methods used to refine taxonomic resolution, manage time use and autocorrelation through sub-sampling, extract behavioural metrics applied to ecological processes, and for automating abundance estimates and image classification with the goal of providing a resource for researchers. [ABSTRACT FROM AUTHOR]

The use of quantitative broadband echosounders for biological studies and surveys can offer considerable advantages over narrowband echosounders. These include improved spectral‐based target identification and significantly increased ability to resolve individual targets. An understanding of current processing steps is required to fully utilise and further develop broadband acoustic methods in marine ecology.We describe the steps involved in processing broadband acoustic data from raw data to frequency dependent target strength (TSf) and volume backscattering strength (Svf) using data from the EK80 broadband scientific echosounder as examples. Although the overall processing steps are described and build on established methods from the literature, multiple choices need to be made during implementation.To highlight and discuss some of these choices and facilitate a common understanding within the community, we have also developed a Python code which will be made publicly available and open source. The code follows the steps using raw data from two single pings, showing the step‐by‐step processing from raw data to TSf and Svf.This code can serve as a reference for developing custom code or implementation in existing processing pipelines, as an educational tool and as a starting point for further development of broadband acoustic methods in fisheries acoustics. [ABSTRACT FROM AUTHOR]

Fish avoidance of vessels can bias fisheries-independent surveys. To understand these biases, recordings of underwater radiated vessel noise from a noise-reduced and a conventional research vessel were played back at the same sound pressure levels (SPL) as experienced in situ to Atlantic herring (Clupea harengus) in a net pen at two different densities. The noise-reduced vessel recording was also scaled to the same SPL as the conventional vessel to test if characteristics other than SPL affected the reactions. Overall, only weak reactions were observed, but reactions were stronger in the low-density school, in the middle of the pen, and for the scaled silent vessel compared with the conventional vessel. These observations may be attributable to the lack of low frequencies ( Les reactions d'evitement de poissons face a des navires peuvent biaiser les inventaires independants de peche. Afin d'evaluer l'etendue de tels biais, une experience de repasses de sequences sonores a ete effectuee sur des bancs de harengs atlantique (Clupea harengus), de densites differentes, places dans des enclos en filet. Les sequences sonores utilisees comprenaient des enregistrements d'un navire conventionnel et d'un navire a niveaux sonores reduits,<>, toutes presentees aux memes niveaux de pression acoustique (NPA) que ceux auxquels les harengs sont generalement soumis in situ. Le navire a niveaux sonores reduits a egalement ete rehausse aux memes NPA que ceux produits par le navire conventionnel afin de determiner si des facteurs autres que les NPA peuvent affecter les reactions d'evitement des harengs. En general, seules de faibles reactions aux sequences sonores ont ete observees. Cependant, de plus fortes reactions ont ete observees pour le banc de faible densite comparees au banc de forte densite, ainsi que de plus fortes reactions lors de repasses de sequences sonores rehaussees du navire silencieux comparees au navire conventionnel. De telles observations peuvent etre expliquees soit par l'absence de basses frequences (, Introduction It has been documented that fish avoid research vessels, which can cause bias in fisheries-independent acoustic-trawl surveys of fish stock biomass (Mitson 1995; De Robertis and Handegard 2013). These [...]

To assess potential disturbance effects on fish from seismic air-gun surveys, we described several metrics to characterize the exposures from such surveys, including the number of emissions by area and time, and metrics based on accumulated sound exposure levels (SEL). For the SEL-based metrics we used both a simple spherical-geometrical model and a model that incorporated physical sound propagation properties such as bottom topography and the vertical difference in sound speed. We applied the metrics to two experiments in Norwegian waters (the Nordkappbanken and Vesteralen experiments) where fish distributions and fisheries were affected by the air-guns, but where the disturbance was stronger in the Nordkappbanken case. The metrics based on the number of emissions by area and time showed a stronger impact in the Nordkappbanken case. For the SEL-based metrics, the simple sound propagation model failed because of artificially elevated levels close to the emissions, but for the more complex propagation model, contrary to expectations, a stronger SEL was found in the Vesteralen case. We conclude that simple sound propagation models should be avoided and that the reliance on sound energy metrics like SEL for disturbance effects must be interpreted with caution. Dans le but d'evaluer les possibles effets que peuvent avoir les echantillonnages sismiques par canons a air, nous decrivons differentes metriques permettant de caracteriser l'exposition de telles pratiques d'echantillonnage. Ceci inclut le nombre d'emissions par zones et periodes ainsi que les metriques basees sure les niveaux accumules d'exposition sonore (SEL). Nous avons utilises deux modeles distincts de propagation du son. En particulier, le second modele integre les proprietes physiques de la propagation du son comme la topographie ou la difference verticale de vitesse du son. Nous avons applique les metriques a deux etudes lors lesquelles les distributions des poissons ainsi que le succes de peche ont ete affectes. Le niveau de perturbation reporte etait plus important lors de la premiere etude. Les metriques basees sur le nombre d'emissions en fonction de la zone et de la periode montrent une exposition sonore plus forte lors de la premiere etude. Pour les metriques basees sur les SEL, si le modele de propagation simple du son n'apparait pas satisfaisant du fait de niveaux artificiellement eleves proche de la source d'emission, le second modele de transmission, et ce contrairement a nos attentes, detecte un SEL plus fort lors de la seconde etude. Nous concluons que les modeles de propagation simple du son ne devraient pas etre employes et que l'utilisation de metriques tel que le SEL pour des effets de perturbation se doivent d'etre interpretes avec precaution., Introduction Geological (air-gun) surveys map the sub-bottom structures of the sea floor and are used extensively for locating petroleum resources. The air-gun arrays are designed to create an acoustic pulse [...]

The effective sampling volume of trawl and acoustics is an important parameter in fish abundance estimation surveys. This paper presents a method to compute the probability of a fish being available to the bottom trawl and the probability of it being seen on the echo sounder, given its initial position relative to the vessel path. These probabilities are then related to the calculation of the effective observational volume for trawl and acoustics, the two main tools of measuring abundance of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). As an example, the computation is carried out for a typical vertical distribution in the Barents Sea. Our model is based on an Ornstein- Uhlenbeck model for the fish swimming trajectories, and its parameters are estimated using observations of swimming trajectories for individual fish, recorded by a split-beam echo sounder. The model itself constitutes a general method to translate observations on behaviour of individual fish to probability maps. The results indicate a typical fishing height of 20 m for the bottom trawl, but it is also shown that there is a relatively low probability of catching by the trawl what you see on the echo sounder, even for fish positioned directly in the trawl path. This is because of strong lateral movements of the fish. Le volume effectivement echantillonne est une variable importante dans les inventaires d'abondance des poissons fans par chalutage ou par acoustique. Notre travail presente une methode pour calculer la probabilite qu'un poison soft accessible au chalut de fond et qu'il soft visible sur l'echosondeur, etant donne sa position initiale relative a la trajectoire du navire. Ces probabilites peuvent ensuite etre reliees au calcul du volume effectif obtenu par chalutage ou acoustique, les deux outils principaux pour mesurer l'abundance de la morne franche (Gadus morhua) et l'aiglefin (Melanogrammus aeglefinus). Le calcul dune repartition verticale typique de la mer de Barents est donne en example. Notre modele se base sur le modele d'Ornstein-Uhlenbeck des trajectoires de nage des poisons et les parametres sont estimes a partir d'observations de trajectoires de nage de poisons individuels enregistrees par un echosondeur a faisceau divise. Le modele lui-meme represente une methode generale pour traduire des observations faites sur un seul poison individuel en canes de probabilite. Nos resultats indiquent que la hauteur moyenne typique de peche d'un chalut de fond est de 20 m, mais aussi qu'il y a une probabilite relativement faible de capture par le chalut des poisons visibles a l'echosondeur, meme pour les poisons places directement dans la trajectoire du chalut; cela s'explique par (importance des deplacements lateraux des poisons. [Traduit par la Redaction], Introduction Two problems in fish survey methodology that have been subject to intense research are (i) absolute abundance estimation (Loland et al. 2007) and (ii) relating bottom trawl and acoustic [...]