Dispersal of early life stage haddock (Melanogrammus aeglefinus) as inferred from the spatial distribution and variability in length-at-age of juveniles

In southwestern Nova Scotia, haddock (Melanogrammus aeglefinus) spawning is centered on Browns Bank where the variability of a partial gyre influences the distribution of eggs and larvae. An unknown proportion of each year-class is advected northward to the Bay of Fundy. We examined the variability in length at age 2 as an index of retention during early life. We assumed that early life stages that are retained in the Scotian Shelf area grow more slowly, while those that are advected into the Bay of Fundy grow more quickly. An optimization program was used to estimate the proportions of Scotian Shelf and Bay of Fundy sized components in length at age 2 bimodal frequency distributions for year-classes 1968-1993. The median proportion of Scotian Shelf sized fish was 0.89. A physical circulation model showed that the majority of particles released on Browns Bank drifted towards the Bay of Fundy. Results of the physical model and the size-based index differ partly because the former predicts the fate of passive particles, while the latter is an integrated measure of the proportion of fish retained and surviving. Survival is associated with high wind stress (r = -0.5, p = 0.011, n = 25) implying a higher probability of survival of those retained in the Scotian Shelf region.