Fisheries Research 107 (2011) 283–290 Contents lists available at ScienceDirect Fisheries Research journal homepage: www.elsevier.com/locate/fishres Do drifting and anchored Fish Aggregating Devices (FADs) similarly influence tuna feeding habits? A case study from the western Indian Ocean S. Jaquemet a,∗ , M. Potier b , F. Ménard b a Université de la Réunion, Laboratoire d’Ecologie Marine, 15 avenue René Cassin BP 7151 97715 Saint Denis, Réunion Island, France b IRD, UMR 212 EME (Exploited Marine Ecosystems) (IRD/IFREMER/UM2), Centre de Recherche Halieutique Méditerranéenne et Tropicale, Avenue Jean Monnet, BP 171, 34203 Sète Cedex, France article info Article history: Received 21 May 2010 Received in revised form 4 November 2010 Accepted 9 November 2010 Keywords: Tropical tunas FADs Ecological Trap Diet Western Indian Ocean abstract Anchored and drifting Fish Aggregating Devices (FADs) are intensively used in tropical tuna fisheries. In both small-scale and industrial fisheries, skipjack (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) are the main targets. The increasing development of this fishing practice by industrial purse seiners has raised the question of the impact of FADs on tuna communities, as they might act as an ecological trap. This study investigated the feeding habits of skipjack and yellowfin tuna associated with anchored and drifting FADs in the western Indian Ocean. The diet of 352 tunas was analysed taking into account the type of FAD, ontogenetic variations, and the resources richness of the area. Poor-food and rich-food areas were defined according to the abundance of stomatopod Natosquilla investigatoris, the main prey of tunas, on the fishing sites. Diet composition was expressed through functional groups of prey. Significant dietary differences were found between both FAD types, as well as an effect of individual size. Around anchored FADs tuna preyed on diverse assemblages of coastal fish and crustacean larvae and juveniles, whereas a low diversity of epipelagic prey dominated the tuna diet associated with drifting FAD. Compared to anchored FADs, the frequency of empty stomachs was significantly higher and the stomach content mass significantly lower among skipjack and small yellowfin tunas caught around drifting FADs. This was magnified in poor-food areas, where drifting FADs often evolved, suggesting that these FADs could negatively impact the growth of skipjack and small yellowfin tuna. Larger yellowfin tuna exhibited differences in their dietary habits between anchored and drifting FADs, and between poor-food and rich- food areas. However, drifting FADs did not impact them as strongly as juveniles of yellowfin or skipjack tunas. Our study gives new highlights on possible detrimental effects of FAD on tunas, and this has to be considered in future sustainable management strategies of tuna fisheries. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Fish naturally associate with floating objects in almost all oceans in the world (Fréon and Dagorn, 2000; Castro et al., 2002). This aggregating behaviour is used in small-scale and industrial tuna fisheries so as to concentrate fish around man-made Fish Aggre- gating Devices (FADs), and then so increase the catches. Among fish, tropical tunas such as skipjack (Katsuwonus pelamis) and yel- lowfin tunas (Thunnus albacares) frequently associate with floating objects at the surface of the oceans (Gooding and Magnuson, 1967; Fontenau et al., 2000). As a consequence, since the early 1990’s, drifting FADs are used in the open ocean and anchored FADs in inshore local tropical fisheries; these devices play an important role in all tropical and sub-tropical tuna fisheries nowadays (Fonteneau, ∗ Corresponding author. Tel.: +262 262938775; fax: +262 262938685. E-mail address: sebastien.jaquemet@univ-reunion.fr (S. Jaquemet). 2000; IATTC, 2002). In the western Indian Ocean, anchored FADs are used in small-scale fisheries, and sets around drifting FADs are a common practice for the industrial purse seine fishery (Tessier et al., 2000). The reason why fish aggregate so frequently with FADs at the surface of the ocean is still poorly understood. Six main hypothe- ses have been stated: sheltering, seamark in the ocean, meeting point, resting, feeding, and indication of area of high production (Gooding and Magnuson, 1967; Hunter and Mitchell, 1967; Dagorn et al., 2000; Fréon and Dagorn, 2000; Castro et al., 2002). In addi- tion, several authors suggested that tunas might be trapped around man-made FADs (Marsac et al., 2000), which could lead to an inappropriate habitat selection, and have detrimental effects on their short-term health (Hallier and Gaertner, 2008). According to the ecological trap hypothesis, man-made FADs could drift to non-productive areas and then reduce the feeding activities of asso- ciated tunas, which would negatively impact the dynamics of the populations. In the actual context of overfishing and rapid deple- 0165-7836/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2010.11.011