In the ice-covered southeastern Hudson Bay (northern QuCbec, Canada), marine fish exhibited 2 distinct reproduction strategies. Sand lance Amrnodytes sp. and Arctic cod Boreogadus saida produced large numbers of small larvae that hatched before the ice break-up when the abundance of prey (copepod eggs and nauplii) was low. Feeding incidence was low and the larvae fed on relatively small prey. A morphometric index of condition suggested that the 2 species suffered from starvation at first feeding. This critical period was approximately synchronized with peak abundance of prey, possibly an adaptation to minimize starvation mortality. Shchaeidae and Cottidae produced small numbers of large larvae that fed efficiently on relatively large prey before yolk resorption. These larvae emerged after the ice break-up, when phytoplankton production was well under way and prey were abundant. Interannual variations in the timing between first feeding and the production of prey could influence recruitment in sand lance and Arctic cod but are unlikely to affect the early survival of Stichaeidae and Cottidae.
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.
In ice-covered southeastern Hudson Bay (northern Quebec, Canada), the foraging of firstfeeding Arctic cod Boreogadus saida and sand lance Ammodytes sp. was adversely affected by the plume of the Great Whale River. Before the freshet, marine fish larvae and their potential prey were marginally more abundant offshore where porous sea ice supported the development of ice algae than inshore where freshwater ice prevented algal growth. Larval fish foraging under the ice appeared limited by prey availability in the diluted (S < 5 %c), 5 m thick, surface layer and by light availability in the underlying marine waters. Arctic cod larvae which avoided the freshwater surface layer did not feed. The more euryhaline sand lance were present in the surface layer and fed to some limited extent until the freshet when further light attenuation by the turbid waters of the expanding plume completely halted their foraging activity. Feeding resumed in sand lance and started in Arctic cod at the ice breakup when the fragmentation of the ice cover and the vertical mixing of the plume allowed light to penetrate at depth. An anthropogenic reduction of the Great Whale River discharge in spring would generally improve local feeding conditions for marine fish larvae that occur under the ice. The impacts of such a reduction on the productivity of the coastal zone in summer remain to be assessed.
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