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Marine Ecology Progress Series

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MEPS 337:197-208 (2007)  -  doi:10.3354/meps337197

Spatio-temporal variation in diet may affect condition and abundance of juvenile European hake in the Gulf of Lions (NW Mediterranean)

Franck Ferraton1,2,*, Mireille Harmelin-Vivien2, Capucine Mellon-Duval1, Arnaud Souplet1

1Centre de Recherche Halieutique Méditerranéenne et Tropicale, IFREMER, Laboratoire Ressources Halieutiques, Avenue Jean Monnet, BP 171, 34203 Sète Cedex, France
2Centre d’Océanologie de Marseille, Université de la Méditerranée, CNRS UMR 6540, Station Marine d’Endoume, rue Batterie des Lions, 13007 Marseille, France

ABSTRACT: Variations in space and time of juvenile hake diet (5 to 19 cm total length, TL) were investigated in the Gulf of Lions (NW Mediterranean) and related to variation in C and N stable isotope ratios, condition and abundance. Crustaceans (mysids and euphausiids) dominated the diet of the smallest juvenile hake (5 to 9 cm TL), and fishes (sardines and anchovies) of the largest juveniles (15 to 19 cm TL). The transition from a crustacean- to a fish-based diet occurred in medium-sized juveniles (10 to 14 cm TL), which preyed on both crustaceans and fishes (gobiids). These juveniles preyed on fishes when living in shallow waters (30 to 50 m), and crustaceans when located in deep waters (70 to 150 m). Although hake diet did not change over time in shallow waters (fish-based diet), in deep waters it was dominated by mysids and euphausiids in 2002 and natantids in 2003. In the size range analysed, no correlation was found between juvenile hake length and their δ13C and δ15N values, but a significant correlation with depth was observed, with higher values in shallow waters. The condition factor of medium-sized juveniles did not vary with depth in 2002, but was significantly lower in deep waters in 2003 when they fed on natantids instead of small crustaceans. Abundance of juvenile hake in the Gulf of Lions drastically decreased from 2002 to 2003, particularly in deep waters. The lower condition factor of juvenile hake in deep waters in 2003, probably owing to a lack of suitable food, might have negatively affected their survival. These results support the hypothesis that food resources influence condition and survival of juvenile hake when settled, and thus affect NW Mediterranean fisheries.

KEY WORDS: Merluccius merluccius · Stomach contents · Stable isotopes · Carbon · Nitrogen · Relative condition factor · Recruitment

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