From April 2003 to April 2004 monthly sea surveys were conducted around 2 fish aggregating devices (FADs) moored at 2000 and 2500 m depth in Martinique (Lesser Antilles). The use of a dual frequency splitbeam echosounder combined with an underwater camera and fishing methods allowed assessment of average space and time distribution of pelagic fish aggregated beneath the FADs, as well as identification of their overall size and species composition. At daytime, 4 fish aggregations were identified at each FAD, representing 4 distinct types: i) an aggregation of small juvenile tuna (mean fork length, FL: 30 cm) observed very close to the surface in 25% of daytime periods; ii) a small surface aggregation dominated by carangids, Caranx crysos, present in 65% of daytime periods; iii) a large sub-surface aggregation observed during all daytime periods: this aggregation appeared to be primarily comprised of 58 cm FL blackfin tuna (Thunnus atlanticus), mixed with yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas of the same size; and iv) sub-surface scattered large predators (mainly blue marlin, Makaira nigricans) present in 10% of daytime periods. A smaller sub-surface aggregation comprised of medium tuna mixed with “extranatants” (fishes which remain within 10 to 50 m of a FAD) was observed in 75% of night-time periods, whereas unidentified scattered fishes were detected from 70 to 400 m depth. The low daytime vulnerability of medium sub-surface tunas to applied line techniques leads us to assume that their feeding motivation was low during daytime. These tunas could preferentially feed on mesopelagic organisms during night-time and transition periods around Martinican moored FADs. Local fishermen mainly targeted the large scattered predators using very small tunas as living bait. The sub-surface tuna aggregation hence appeared to be currently unexploited by local fisheries, though it represented the large majority of the pelagic biomass around the moored FADs.

This paper examines the fishing of blackfin tuna (Thunnus atlanticus) around Fish Aggregating Devices (FADs) in Martinique (French West Indies). It is based on the compared analysis of catches from monthly experimental fishing surveys and sampling of commercial landings. The data collected in these two different ways allowed comparison of blackfin tuna length frequencies. A large part of the commercial landings were made up of young immature tuna with a fork length of less than 40 cm, whereas the experimental longline catches were mainly made up of fish with a fork length ranging between 55 and 75 cm. We give evidence that these discrepancies were mostly due to the fishing technique used. Indeed, contrarily to the experimental surveys, Martinican fishermen only fish during daytime and usually on the surface by trolling. This way, fishermen do not have access to the largest fish, which are found deeper. Our results suggested that a new fishing technique such as vertical longlining, could improve commercial catches of big blackfin tuna under FADs.

Depuis une quinzaine d’années le développement despêcheries artisanales des pays insulaires est basé sur la pêche desgrands pélagiques à partir de l’introduction d’une innovationmajeure, à savoir l’immersion de dispositifs de concentration de poissons(DCP ancrés). Face à cet engouement récent et aux résultatstrès mitigés, voire aux échecs, souvent observés,l’article propose une démarche méthodologiqued’élaboration d’un cadre d’évaluation permettant unclassement de la diversité et complexité des transformations induites parl’introduction des DCP et une estimation de la durabilité de leurintégration. La notion de durabilité intègre ici des objectifs àla fois écologiques quant à la conservation de la ressource etsocioéconomiques en termes de maîtrise et d’acceptation d’uneinnovation devant favoriser l’évolution du système. Cette analyseest effectuée en croisant plusieurs points de vue disciplinaires –biologique, géographique, économique et sociologique – et encomparant différentes expériences relevant de contextes et decommunautés de pêcheurs variés. Le cadre d’évaluation secompose d’une série de 21 indicateurs de nature biologique, technique,économique et sociale. Une illustration est proposée à partir de troisexemples représentatifs de la diversité des situations : LaRéunion, les Comores et l’archipel du Vanuatu. Sur la base d’uneévaluation aux dires d’experts, chacun de ces critères faitl’objet d’une notation selon une échelle de 0 à 5 en fonctiondu caractère inexistant, incertain, notable ou pérenne des effetsobservés. Enfin dans un souci de d’opérationnalité etd’aide à la décision, une présentation graphique desynthèse est élaborée pour faciliter les comparaisons et identifierles points critiques.

This paper compares the species composition of free swimming schools and schools associated with fish aggregating devices (or FADs) observed by scientists in the eastern equatorial Atlantic during the early eighties and late nineties. This comparison shows that in free swimming schools, big changes in the species composition have occurred. The main change is a rarefaction of mixed species free schools (skipjack and small yellowfin or bigeye). This change is probably a real biological one, and possibly a consequence of the large numbers of FADs seeded in the area since 1990. Nowadays, most small tuna living in the equatorial area appear to be concentrated under these drifting FADs instead of in free schools. Further study is recommended in order to evaluate the validity and interpretation of this result and to examine its implications.