Metapopulation theory and northern cod population structure: interdependency of subpopulations in recovery of a groundfish population

Abstract

The spatial structure of the northern Atlantic cod ( Gadus morhua) population inhabiting the coastal and offshore regions of eastern Newfoundland and Labrador is analyzed using metapopulation concepts. Evidence for subpopulation structure is drawn from published studies of spawning times and locations, life history traits, and genetic differentiation. Putative subpopulations are associated with spawning areas near offshore banks and in coastal bays. Metapopulation theory predicts that fewer spawning areas would be occupied as the population declines. This prediction is substantiated in that Saglek, Nain, Makkovik and Harrison Banks have had no significant spawning activity since the over-exploitation of the northern cod by trawlers during the 1960s. The corollary prediction is that as the population recovers, currently unoccupied spawning areas will be recolonized. The model suggests a continued moratorium on fishing the remaining subpopulations would promote recolonization and accelerate the recovery of the overall metapopulation. There are limitations in the application of metapopulation theory to marine fish populations such as the northern cod. However, fisheries management strategies for stock rebuilding would benefit from research which improves our understanding of the interdependency of subpopulations, the persistence of the overall population, and the processes involved in recovery of a collapsed metapopulation.