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climate indices, the North Atlantic Oscillation index (NAO, Hurrell et al., 2001; Rogers,

1984) and the Length Of the Day index (LOD, McCarthy and Badcoc, 1986), as well as

the temperature for the following reasons:

• Several studies have documented the impact of the NAO on the North Atlantic food

web (e.g. Fromentin and Planque, 1996) as well as its influence on the reproduction,

growth and spatial distribution of fish, such as herring, cod and albacore (Alheit and

Hagen, 1997; Bard, 2001; Ottersen et al., 2001). For all these reasons, the NAO could

affect directly and indirectly the spatial and temporal dynamics of Atlantic BFT

population (Marsac, 1999).

• Klyashtorin (1998) put forward that trends in catch of small pelagic fish on which

BFT feeds (Mather et al., 1995) were closely related to the Atmospheric Climatic Index

(ACI, Girs, 1974). ACI is tightly correlated with a global geophysical index, the excess

th
Length Of the Day (LOD). As this last index is available since the 17 century, we can

test possible relationships between BFT long-term fluctuations and LOD.

• Temperature influences fish life history at various stages, i.e. larval growth and

mortality (Otterlei et al., 1999; Pepin, 1991), timing of food availability for early ages

(Ellersten et al., 1989), growth (Brander, 1995), maturity (Tyler, 1995), timing of

spawning (Hutchings and Myers, 1994) and egg viability (Flett et al., 1996).

Temperature has been also shown to play a key role in spawning activity of both

tropical and temperate tunas (which spawn in warm water generally > 24°C, Fromentin

and Fonteneau, 2001; Nishikawa et al., 1985; Schaefer, 2001). Temperature is also

known to influence the production and distribution of plankton (e.g. McGowan et al.,

1998; Beaugrand et al., 2002) and subsequently, the food resource for juvenile and

adults BFT (Mather et al., 1995). Thus, changes in temperature could also affect the

spatial and temporal dynamics of Atlantic BFT.

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