Advection of continental water as an export mechanism for anchovy, Engraulis encrasicolus, larvae

Abstract

The presence of a surface layer of a less saline water of continental influence (CIW) along the continental slope off the Catalan coast (NW Mediterranean) was observed in June 1995. This CIW was formed in the Gulf of Lions from Rhône runoff and carried by the current associated with the shelf-slope front. This study analyses the spatio-temporal behaviour of that water of continental influence in relation to the shelf-slope front, and its effect on the distribution of fish larvae, in particular the larvae of the anchovy, Engraulis encrasicolus. Displacements of the front are observed to follow an oscillation with a period of eight days and an amplitude of 10 km. Anchovy larvae were associated with the presence of CIW, whereas the oceanic species Hygophum benoiti appeared in the region of the slope when the front, and the associated CIW layer, moved close inshore during its oscillation. The size frequency distribution for the anchovy larvae trapped within the CIW suggests that the larvae had been spawned further north, near the Gulf of Lions. It is concluded not only that larvae were transported by the current but also that their development had taken place entirely inside the CIW. The possible benefit to the survival of anchovy larvae of being kept inside that water, though they have been carried far from their spawning areas, is discussed in the basis of fluorescence and microzooplankton data.