A review of the evidence for genetic structure of cod (Gadus morhua) populations in the NW Atlantic and population affinities of larval cod off Newfoundland and the Gulf of St. Lawrence

We review our recent studies on the genetic structure of Atlantic cod (Gadu s morhua) populations in the NW Atlantic. Our conclusions are based on know ledge of polymorphism at microsatellite DNA loci combined with known aspect s of cod biology and ecology and with known oceanographic features in the N W Atlantic. Three case studies illustrate genetic heterogeneity between cod populations at the meso- and large-scales of coastal embayments and offsho re banks and at the small-scale of oceanographic features. Our results gene rally highlight the importance of combining genetic with physiological, eco logical, and oceanographic information, when assessing the genetic structur e of highly abundant, widely distributed, and high gene-flow marine fish sp ecies. We highlight the role that oceanographic features (e.g., gyre-like s ystems) and known spatio-temporal differences in spawning time may play as barriers to gene-flow between and among neighboring and often contiguous co d populations in the NW Atlantic. We suggest that bathymetric and hydrodyna mic/oceanographic structure represents a rational starting point for develo ping hypotheses aimed at assessing the genetic structure of high gene-flow marine fish species. (C) 1999 Elsevier Science B.V. All rights reserved.