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to long-term fluctuations in BFT trap catches. The present results highlight a significant,

but negative, relationship between temperature and trap catches. In other words, with

warmer weather, fewer BFT were caught in the Mediterranean and Gibraltar strait.

However, high temperature is expected to enhance recruitment, since the maturation and

reproductive activities of tuna species (among which BFT) require temperature

generally > 24°C (Bye, 1989; Mather et al., 1995; Schaefer, 2001; Stacey, 1989).

Consequently, the relationship between temperature and BFT recruitment is expected to

be positive and not negative. Therefore, we tend to dismiss the hypothesis of changes in

BFT recruitment (and probably growth, but this assumption would need further

information and investigation) in relation to temperature.

The negative relationship between long-term fluctuations in temperature and BFT

trap catches could be more easily explained by changes in migration patterns. Changes

in environmental conditions are also known to influence spatial and temporal

distribution and/or migration patterns of fish (e.g. Brill and Lutcavage, 2001; Dickson

and Brander, 1993; Lehodey et al., 1997; Southward et al., 1988). BFT is a large

pelagic fish, which carries out a large migration over the North Atlantic for feeding and

spawning. It is caught by the trap fishery when it migrates into the Mediterranean Sea to

reproduce (Mather et al., 1995; Ravier and Fromentin, 2001). Fluctuations in trap

catches could, therefore, result from changes in spawning migrations attributable to

modifications in oceanographic conditions.

Natal homing, opportunism… or something in between?

Atlantic BFT is generally believed to visit each year one of its two identified

spawning sites: the Western Mediterranean Sea (mainly around Balearic islands and

Sicily) on the one hand, and the Gulf of Mexico on the other (Mather et al., 1995). The

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