Seasonal spawning and wind-regulated retention-dispersal of early life stage Atlantic cod (Gadus morhua) in a Newfoundland fjord

Sequential ichthyoplankton surveys were used to determine the spatial and temporal distribution of eggs and larvae over coastal spawning grounds of Atlantic cod (Gadus morhua) in Smith Sound, Trinity Bay, Newfoundland, during the spring and summer of 2006 and 2007. Egg densities showed similar patterns for both years with two peaks in abundance in spring (March-April) and late summer (late July). A clear progression of development stages (1-4) was observed in spring and summer in 2006 and summer in 2007, suggesting retention of eggs within the Sound during these periods. Modelled predictions of vertical egg distributions indicated eggs were broadly distributed near the surface during spring (March-April), but were concentrated below the pycnocline (> 10 m) within the inner portions of the Sound during the summer months (July-August). Back-calculated peaks in spawning based on water temperatures were estimated at 11 and 4 April for 2006 and 2007, respectfully, with late season peaks centred on 21-24 July for both years. Environmental data indicated cooler water temperatures and periods of high wind stress in spring, and warmer, calmer periods late summer, consistent with higher retention and faster development times on the spawning grounds later in the season. We conclude that spring and summer spawning events result in different distributions of early life stages and may lead to different distributions of juvenile and adult fish.