MEPS 366:175-186 (2008)  -  DOI:

Visual censuses around drifting fish aggregating devices (FADs): a new approach for assessing the diversity of fish in open-ocean waters

J. C. Gaertner1,*, M. Taquet2, L. Dagorn3, B. Mérigot1, R. Aumeeruddy4, G. Sancho5, D. Itano6

1Centre d’Océanologie de Marseille, Université de la Méditerranée, LMGEM, UMR CNRS 6117, Rue de la batterie des Lions 13007 Marseille, France
2Institut français de recherche pour l’exploitation de la mer (IFREMER), and 3Institut de Recherche pour le Dévelopement, CRH, Avenue Jean Monnet BP 171 – 34203 Sète Cedex, France
4Seychelles Fishing Authority, Fishing Port, PO Box 449, Victoria, Mahé, Seychelles
5College of Charleston, Grice Marine Laboratory, 205 Fort Johnson Road, Charleston, South Carolina 29412, USA
6Pelagic Fisheries Research Program, University of Hawaii, 1000 Pope Road, MSB 312, Honolulu, Hawaii 96822, USA

ABSTRACT: This study provides a baseline measure of pelagic fish species diversity around fish aggregating devices (FADs) in the Western Indian Ocean. Using data from visual censuses made by SCUBA divers around drifting FADs we (1) analysed 11 diversity indices describing 4 main components of pelagic diversity: number of species, evenness, taxonomic diversity and rarity and (2) discussed the viability of using visual censuses around FADs to monitor temporal and spatial changes in diversity patterns of pelagic fishes in the future. Our results not only show that a single index, such as species richness or the Shannon-Wiener index, cannot provide a complete description of pelagic fish diversity around FADs, but also that some components of diversity appear to be multifaceted themselves and require the simultaneous use of several complementary indices in order to be accurately described and monitored. Despite a limited sampling effort, our results suggest that using visual censuses around FADs could provide reproducible ‘relative’ indices of diversity for a well-delimited assemblage of species (intra- and extranatant species in the epipelagic domain). In this context, we propose a preliminary ‘short list’ of diversity indices based firstly on their complementarity and secondly on their simplicity. While visual censuses of pelagic fishes at FADs (like any other sampling method) cannot give an exhaustive picture of diversity, they are a fishery-independent survey method that can complement other sampling techniques and provide reproducible information to monitor the diversity of these very difficult-to-access pelagic fish communities.

KEY WORDS: Pelagic fishes · Diversity · Drifting FADs · Indian Ocean

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Cite this article as: Gaertner JC, Taquet M, Dagorn L, Mérigot B, Aumeeruddy R, Sancho G, Itano D (2008) Visual censuses around drifting fish aggregating devices (FADs): a new approach for assessing the diversity of fish in open-ocean waters. Mar Ecol Prog Ser 366:175-186.

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