Match/Mismatch and Other Constraints in the Early Life of Arctic Cod (Boreogadus saida), the Fulcrum Species of Marine Arctic Ecosystems

In the extremely pulsed ecosystem of Arctic seas, the hatching of fish larvae should match precisely the short vernal bloom of microalgae and peak production of copepod nauplii. However, in seas influenced by large rivers the hatching of Arctic cod begins as early as January during the frigid polar night well before microalgal production, and ends in early July at peak production of prey. It has been hypothesized that, in these seas, the underice freshwater plume of rivers provides a winter thermal refuge for larvae, allowing fish to hatch early in the year and attain a large size before freeze-up in October. In the fall, freshly metamorphosed early hatchers migrate to the continental slope where they join their adult cannibalistic congeners to overwinter in the warm Atlantic layer. A large pre-winter size would minimize vulnerability to cannibalism during winter. We suspect that late hatching arctic cod enjoying peak prey availability at first feeding in June and July have not yet metamorphosed at freeze-up and recruit to the sea-ice ecosystem to overwinter. Evidences for these two different early life strategies in arctic cod and other species are presented, and perspectives to further test these hypotheses are discussed.