Quantifying the interplay between environmental and social effects on aggregated-fish dynamics

Demonstrating and quantifying the respective roles of social interactions and external stimuli governing fish dynamics is key to understanding fish spatial distribution. If seminal studies have contributed to our understanding of fish spatial organization in schools, little experimental information is available on fish in their natural environment, where aggregations often occur in the presence of spatial heterogeneities. Here, we applied novel modeling approaches coupled to accurate acoustic tracking for studying the dynamics of a group of gregarious fish in a heterogeneous environment. To this purpose, we acoustically tracked with submeter resolution the positions of twelve small pelagic fish (Selar crumenophthalmus) in the presence of an anchored floating object, constituting a point of attraction for several fish species. We constructed a field-based model for aggregated-fish dynamics, deriving effective interactions for both social and external stimuli from experiments. We tuned the model parameters that best fit the experimental data and quantified the importance of social interactions in the aggregation, providing an explanation for the spatial structure of fish aggregations found around floating objects. Our results can be generalized to other gregarious species and contexts as long as it is possible to observe the fine-scale movements of a subset of individuals.Comment: 10 pages, 5 figures and 4 supplementary figure

Les étoiles de mer et leurs cousins - section bibliographique

Section bibliographique du livre : Les étoiles de mer et leurs cousins 80 clés pour comprendre les échinodermes Coralie et Marc TAQUET Editions QUA

Fish aggregating devices (FADs): good or bad fishing tools? A question of scale and knowledge

It is estimated that fish aggregating devices (FADs) are now used for over 40% of world tropical tuna catches, making this technique a major phenomenon for high seas fisheries worldwide, and one that has experienced great expansion over the past three decades. The question of whether the FAD is a good or a bad tool for the exploitation of marine resources depends on many parameters. To respond to this question, it is necessary to distinguish different scales of exploitation (artisanal vs. industrial) and various types of FADs (anchored vs. drifting), but it is also very important to gather more data and conduct further research on this topic to gain a better understanding of the phenomenon and of its impacts. As such, twelve years after the first international conference devoted to FADs, which was held in Martinique (French West Indies), a new multi-scalar global assessment of FAD fisheries development and a review of the progress of research in this field was deemed vital. The latest international conference, “Tuna Fisheries and Fish Aggregating Devices”, was held in Tahiti in November 2011, and it was an event that welcomed nearly 150 conference attendees from 40 different countries, three ocean regions, and the Mediterranean. This is an analysis of the relevant literature gathered by the author in the bibliographic database FADBASE. Then, the major issues already addressed by the scientific community are set out, and gaps and research priorities are highlighted for anchored and drifting FADs management

Le redéploiement de la pêche antillaise vers les grands poissons pélagiques

© Ifremer/M. Taquet Introduction Les grands poissons pélagiques exploités aux Antilles sont des espèces appartenant essentiellement aux familles des scombridés (thazards, thon noir, listao, albacore,...), coryphénidés (dorade coryphène), istiophoridés (marlins) et xiphiidés (espadon). Certaines de ces espèces peuvent être capturées près des côtes, soit par des métiers nécessitant peu d’investissement comme la ligne de traîne, soit par des techniques plus complexes comme la senne de plage ou l..

Projet d’implantation de Dispositifs de Concentration de Poissons autour de La Réunion. Rapport final

Dix dispositifs de Concentration de Poissons (DCP) ont été posés autour de la Réunion au cours de l’année 1988. Ces structures, constituées de bouées supportant du matériel attractif (feuillards plastiques et filets), sont mouillées entre 3 et 12 milles nautiques de la côte sur des fonds de 500 à 1500 mètres de profondeurs. Un suivi de l’activité à proximité des DCP a permis d’établir dans la zone proche des DCP. Les thons (Thunnus albacares. Thunnus obesus) et les daurades (Corypheana hippurus) constituent l’essentiel des prises. Il est difficile d’évaluer la réduction des coûts de production qu’induit les DCP, néanmoins le coût d’un DCP est de l’ordre de 1 à 2 % de la production en valeur dans la zone proche des DCP, ce qui paraît un résultat satisfaisant et qui, de plus, est susceptible d’être amélioré

Prospection des ressources côtières démersales profondes autour de La Réunion. Analyse des données des campagnes à la mer réalisées du 23/02/2000 au 28/07/2000. Rapport de synthèse des travaux confiés par le CRPMEM de La Réunion à l’Ifremer Délégation Océan Indien.

Data on the potential exploitation of deep demersal fish species in Reunion Island are very limited. The Regional Comitee for Sea Fisheries and Marine Breeding, with the scientific and technical support of Ifremer of La Reunion, has launched prospecting campaigns to identify and characterize deep-sea fish species (between 150 to 600 m deep), with an innovative method of catching with electric reel. The catches made concern mainly 5 main species (yields, frequency of catch, commercial interest). A new species, the brillant pomfret (Eumegistus illustris), as well as the longtail red snapper (Etelis coruscans), are the both main resources that can be exploited by the electric reel technique. They represent more than 60% of the overall catches made during the survey. The other species (red snapper (Etelis carbunculus), shortnose spurdog (Squalus megalops), beryx (Beryx decadactylus),  black snoek (Thyrsitoides marleyi)) are supplements species, given the impossibility to target them, and maintain daily yields at a consistent level with the profitability of the fishing operation. The distribution of these species is strongly related to bathymetry and an assessment of the area available for their habitat around the island, shows that the abundance of these resources is limited to an incompatible level with intensive exploitation. Absence of more precise scientific arguments suggest a precautionary approach and encourages to recommend not favoring the exploitation of new efficient fishing units on this resource but rather to consider it as a potential complementary activity for the fishing units of current small professional fishery, which practice other trades (coral fish species and pelagic fish on FADs with fishing hook).Les données concernant les potentialités d’exploitation des espèces démersales profondes à La Réunion sont très limitées. C’est pourquoi, le Comité Régional des Pêches Maritimes et des Elevages Marins, avec le soutien scientifique et technique de l’Ifremer de La Réunion, a lancé en 2000 des campagnes de prospection pour identifier et caractériser les espèces de poissons profonds (entre 150 à 600 m de profondeur) d’intérêt halieutique, avec une méthode innovante de capture au moulinet électrique. Les captures réalisées concernent principalement 5 espèces d’intérêts halieutiques (rendements, fréquences des captures, intérêt commercial). Une espèce nouvelle, le « mochong » ou « castagnole » (Eumegistus illustris), ainsi que le vivaneau la flamme (Etelis coruscans) constituent les ressources principales exploitables par la technique du moulinet électrique. Elles représentent plus de 60 % des captures globales réalisées lors de la prospection. Les autres espèces (vivaneau rouge (Etelis carbunculus), requin zépine (Squalus megalops), béryx (Beryx decadactylus), snoek (Thyrsitoides marleyi)) n’interviennent qu’en compléments de revenu, compte tenu de l’impossibilité de les cibler et de maintenir des rendements journaliers à un niveau compatible avec la rentabilité de l’exploitation. La répartition de ces espèces est fortement liée à la bathymétrie et une évaluation de la superficie disponible pour leur habitat autour de l’île, montre que l’abondance de ces ressources est nécessairement limitée à un niveau incompatible avec une exploitation soutenue. En absence d’arguments scientifiques plus précis, l’approche de précaution incite à recommander de ne pas favoriser la mise en exploitation de nouvelles unités de pêche performantes sur cette ressource mais plutôt de la considérer comme une activité complémentaire potentielle pour les unités de la flottille de petite pêche professionnelle actuelle, qui pratiquent les autres métiers (pêche à l'hameçon des poissons de fond récifaux et des poissons pélagiques sur DCP)

Age and growth of blackfin tuna (

Daily growth increments measured in the otolith of Thunnus atlanticus were used to estimate the age and growth of individuals, which were sampled from an artisanal fishery operating around fish aggregating devices (FADs) moored off Martinique Island. In this study, 76 otoliths were analysed for fish ranging from 20 to 68 cm fork lengths (FL). The fish were caught using trolling lines at depths ranging from 0 to 10 m. Counts were made, under a light microscope, on the external part of the transverse section of the sagittae, from the primordium to the ventral edge. The mean coefficient of variation of the age reading was 2.4%. To validate readings, the number of increments for 11 individuals was counted using both optic and scanning electron microscopes. The calculated relationship between readings of both methods was found to be linear, with a slope of 1.03 and R2 = 0.99. Frequency of growth increment formation could not be validated. Growth rates derived from otolith readings were, however, compared to those obtained using a modal progression analysis, which was performed on the length-frequency distributions of the landings over a period of two months. The corroboration between the growth rates was good. One increment was assumed to represent one day. The parameters of the von Bertalanffy growth curve for both sexes were L∞ = 71.4 cm FL, k = 0.002 day−1 and t0 = −80 days. According to our results, there is no evidence that Martinican moored FADs act as ecological traps for blackfin tuna. Instead, young blackfin tuna probably leave the vicinity of Martinican moored FADs to undergo a trophic migration at 7 to 8 month-old, and then come back about 8 months later to breed in the Lesser Antilles area

Vulnérabilité des systèmes associés aux monts sous-marins face au changement global

International audienc