Discrete spatial dynamics in a marine broadcast spawner: Re-evaluating scales of connectivity and habitat associations in Atlantic cod ( Gadus morhua L.) in coastal Newfoundland

Abstract

We examined the spatial dynamics of Atlantic cod, Gadus morhua, through its life history on the northeast and southeast coasts of Newfoundland in order to delineate dispersal and critical habitat requirements as potential determinants of appropriate spatial scales for management. Hydroacoustic surveys across the northeast Newfoundland shelf in 1990, 1995, and 2000 showed the distribution of the remaining large aggregations of cod to be concentrated in inshore embayments, which is contrary to historic patterns. Inshore surveys on the south coast identified local spawning aggregations at specific geographic locations, to which adults homed in subsequent years. Dispersal of eggs and larvae to the offshore occurred during spring, but was localized (within bay) in the warm summer months. Abundance of age-0 cod increased with proximity to spawning location inshore, suggesting self-recruitment within local embayments. Age-2–3 juveniles actively selected structurally complex habitat at scales of less than tens of kilometers, with home ranges typically less than 10 ha. Juveniles were associated with specific habitat types, especially at age 0, in both lab and field experiments. Our results suggest that self-recruitment and critical life-history events (e.g., spawning, settlement, and maturity) may occur within local embayments, which currently assume much greater importance to overall cod stock dynamics than in the past. Given evidence for limited dispersal, and the inshore presence of critical habitat for early life-history stages, spatial management tools that consider local dynamics may provide a greater degree of protection for coastal Newfoundland cod than previously thought.