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 (Gadus morhua) populations in the NW Atlantic. Our conclusions are based on knowledge of polymorphism at microsatellite DNA loci combined with known aspects of cod biology and ecology and with known oceanographic features in the NW Atlantic. Three case studies illustrate genetic heterogeneity between cod populations at the meso- and large-scales of coastal embayments and offshore banks and at the small-scale of oceanographic features. Our results generally highlight the importance of combining genetic with physiological, ecological, and oceanographic information, when assessing the genetic structure of highly abundant, widely distributed, and high gene-flow marine fish species. We highlight the role that oceanographic features (e.g., gyre-like systems) and known spatio-temporal differences in spawning time may play as barriers to gene-flow between and among neighboring and often contiguous cod populations in the NW Atlantic. We suggest that bathymetric and hydrodynamic/oceanographic structure represents a rational starting point for developing hypotheses aimed at assessing the genetic structure of high gene-flow marine fish species. (C) 1999 Elsevier Science B.V. All rights reserved.