Export production and the distribution of fish larvae and their prey in a coastal jet frontal region

Fine-scale spatial sampling series and vertical cross-sections were used to obtain quasisynoptic images of the distribution of fish larvae and their prey in the permanent frontal region formed by the Gaspe coastal jet current and the adjacent Anticosti gyre (NW Gulf of St. Lawrence, Canada). The accumulation of large diatoms triggered the reproduction of copepods in the Gasp6 current where eggs and nauplii (the main prey of first-feeding fish larvae) were 10 to 20 times more abundant than in the gyre. Estuarine circulation resulted in the coincidence of the small and abundant larvae of capelin Mallotus villosus and sand lance Ammodytes sp. with this intense production of their food in the jet current. The large and less abundant larvae of redfish Sebastes sp. and Arctic shanny Stichaeuspunctatus exploited the scarcer food resources of the Anticosti gyre. We conclude that opportunistic species producing large numbers of small offspring with limited foraging skills depend on massive export production at hydrographic singularities (i.e. salient hydrographic features) for reproduction. Species producing fewer but larger and more competent larvae can colonize less productive areas of the ocean. Plankton dynamics in the dispersal area of the early larval stages appear to be a pnmary constraint defining the life strategy of a fish species.