International audienceSea cruises were conducted for 57 days over 16 months to characterise pelagic fish aggregations around two moored fish aggregating devices (FADs) in Martinique (Lesser Antilles). Echosounder surveys run in a star pattern were used in conjunction with obliquely beamed sonar observations. An echo-integration-by-shoal algorithm was implemented to isolate pelagic fish shoals from sound scattering layers and to compute mean morphometric, positional and density parameters. Tree regressions were used to select and classify pelagic fish target strengths (TS), with reference to their spatial and temporal characteristics. The main type of pelagic fish aggregation was a large sub-surface aggregation. It was observed during all daytime periods within a radius of 400 m. of the FAD. A smaller type of aggregation was observed closer to the surface and to the FAD in 65% of daytime periods. Large scattered fish were observed in 16% of daytime periods. At night, a medium-sized aggregation was detected in the sub-surface in 75% of night-time periods. The sizes of the fish inside the aggregations (determined from TS values) were lower in the small near-surface aggregation than in the large sub-surface aggregation. Mean packing densities of sub-surface medium fish and near-surface small fish aggregations (determined from TS and shoal acoustic density) were respectively 0.2 and 1.3 fish per m(3). The acoustic methodology and results are discussed with reference to the characteristics and performance of the echosounder and to the spatial structure of pelagic fish aggregations around moored FADs in Martinique

The Pélagiques Gascogne (PELGAS) integrated survey has been developed by a multidisciplinary team of Ifremer and La Rochelle University scientists since 2000, joined by commercial fishermen in 2007. Its initial focus was to assess the biomass and predict the recruitment success of anchovy in the Bay of Biscay in spring. Taking advantage of the space and versatility of R/V Thalassa II, sampling has been progressively extended to other ecosystem components. PELGAS therefore further developed the second objective of monitoring and studying the dynamic and diverse Biscay pelagic ecosystem in springtime. The PELGAS survey model has allowed for the establishment of a long-term time-series of spatially-explicit data of the Bay of Biscay pelagic ecosystem since the year 2000. Main sampled components of the targeted ecosystem are: hydrology, phytoplankton, mesozooplankton, fish and megafauna. The survey now provides two main ecosystem products: standard raster maps of ecosystem parameters, and a time series dataset of indicators of the Bay of Biscay pelagic ecosystem state. They are used to inform fish stock and ecosystem-based management, and support ecosystem research. The present paper introduces the PELGAS survey, as a practical example of an integrated, vessel-based, ecosystem survey. The evolution of the PELGAS scientific team and sampling protocols are presented and analysed, to outline factors crucial to the success of the survey. Data and results derived from PELGAS are reviewed, to exemplify scientific questions that can be tackled by integrated ecosystem survey data. Advantages and challenges of the survey are discussed and put into the context of marine ecosystem surveys in the European Marine Strategy Framework Directive and the Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. Common Fisheries Policy. Highlights ► The PELGAS integrated survey conducted since 2000 in spring in the Bay of Biscay is presented. ► PELGAS objectives have switched from the study of the anchovy stock status to ecosystem monitoring. ► Spatially-explicit data have been collected of the main pelagic ecosystem components since 2000. ► Multidisciplinary collaborative working and enough vessel space were critical success factors. ► Finding relevant common scales is essential to analyse ecosystem data within or across compartments.

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-This paper provides an overview of the progress Ifremer has made recently in fisheries acoustics and the study of small pelagic fish by: i) pushing observation frontiers using a range of platforms including an autonomous underwater vehicle, AUV, ii) developing measuring instruments and methods and iii) studying fish distributions. Presently, information from several frequencies of single-beam echosounders is routinely collected together with data from the ME70 multibeam echosounder. For onboard data acquisition control the HERMES software was developed. The new MOVIES 3D software includes modules for simultaneous realistic 3D visualisation and post-processing such as bottom detection, school extraction and calculation of descriptors and integration of all acoustic data. Several data analysis methods are being developed and some initial results are presented. Finally, results on the spatial distribution of small pelagic fish schools in the Bay of Biscay illustrate the role that acoustics can play, and are already playing, in the implementation of an ecosystem approach to fisheries. Key words:Multibeam echosounder / Oceanographic AUV / Pelagic fish / Fisheries acoustics Résumé -Cet article présente une vue d'ensemble des avancées récentes de l'Ifremer en acoustique halieutique et une étude des petits poissons pélagiques tenant compte : i) de l'extension des limites de l'observation, en utilisant une gamme diverse de plates-formes dont un engin sous-marin autonome (AUV), ii) des développements méthodologiques et d'instruments de mesures, iii) de l'étude de la répartition des poissons. Désormais, les données de plusieurs fré-quences des sondeurs mono-faisceaux sont collectées en routine en parallèle à celles du sondeur multifaisceau ME70. Le logiciel HERMES a été développé pour le contrôle de l'acquisition des données à bord. Le nouveau logiciel MOVIES 3D comprend des modules de visualisation réaliste en 3D et de post-traitement (dont la détection du fond, l'extraction de bancs et le calcul de leurs descripteurs ainsi que l'intégration de toutes les données acoustiques). Plusieurs méthodes d'analyse de données sont en cours de développement et quelques premiers résultats sont présentés. Enfin, les résultats relatifs à la répartition spatiale des bancs de petits poissons pélagiques dans le golfe de Gascogne illustrent le rôle actuel et potentiel de l'acoustique dans la mise en place d'une approche écosystémique des pêches.

Characterizing the space–time variability in spatial distributions as well as understanding its drivers is basic to designing robust spatial management plans. As a prerequisite, we analyse here how this variability relates to population dynamics in conjunction with environmental conditions. For that, spatio-temporal statistical approaches are needed but seldom used in fisheries science. To fill this gap, we showcase the usefulness of the method of empirical orthogonal functions (EOFs). Guidelines are given to apply the method on a series of gridded maps as derived from fisheries survey dataseries that now span over decades. The method is applied to the series, 2000–2012, of the spatial distributions of European anchovy in the Bay of Biscay at spawning time. Across the series, the EOF decomposition allowed to identify three main types of spatial distributions. One type corresponded to an extended distribution, another to a restricted distribution in core areas, and the third to a very coastal distribution. The coastal spawning distribution corresponded to a low population growth rate as it was never followed by a large recruitment in the subsequent year. We did not attempt to explain the spatial patterns per se but the drivers of change from one type of distribution to another. Stock size and fish size as well as bottom temperature and water column stratification were the covariates that controlled the variability in the spatial distributions over time. Further, the spatial distribution at spawning time related to recruitment in the following year, meaning that variability in the spatial distribution of spawning affected population dynamics. The typology of maps based on EOF decomposition summarized this spatial variability into spatial spawning configurations, which may serve spatial planning.