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INTRODUCTION

Fish stocks are known to fluctuate extensively over a large range of spatial and

temporal scales (Cushing, 1982; Laevastu, 1993). Several biotic and abiotic processes,

as well as their interactions, may induce such fluctuations. At the beginning of the

century, Hjort (1914; 1926) suggested that fluctuations in stock size depend upon

variations in year-class strength, which are determined at an early stage through various

processes (mainly food availability and environmental conditions for eggs, larvae and

juveniles). Beside larval starvation, other biological factors, such as predation,

competition and cannibalism may also influence the early survival of marine fish

(Bailey and Houde, 1989; Fortier and Villeneuve, 1996; Myers and Cadigan, 1993).

Environmental changes, such as variations in temperature, salinity, wind field and

currents, can affect both the productivity and the distribution of fish stocks (e.g. Alheit

and Hagen, 1997; Cushing and Dickson, 1976; Dickson and Brander, 1993; Lehodey et

al., 1997; Southward et al., 1988). Finally, human exploitation has been extensively

documented to influence fish dynamics and abundance, mainly through overfishing (e.g.

Cook et al., 1997; Hutchings, 2000; Jennings et al., 1998).

In a previous study, Ravier and Fromentin (2001) showed that fluctuations in trap

catches of Mediterranean and Atlantic bluefin tuna (Thunnus thynnus, BFT) may be

decomposed into pseudo-periodic fluctuations of 100-120 years and secondarily of 20

years, which accounted for more than 50% of the total variance. Long-term fluctuations

in catches were further synchronous between distant traps, so that they were likely to

reflect fluctuations in BFT population migrating yearly in the Mediterranean. However,

the causes of such fluctuations remained unclear. The aim of this work is to test whether

the BFT long-term fluctuations might be related to large-scale environmental changes,

using climate indices being available over a long period. We finally retained two

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