Research Document - 1999/035

Population structure of Atlantic cod (Gadus morhua) in the Newfoundland and Labrador area based on microsatellite variation.

By T.D. Beacham, J. Brattey, K.M. Miller, K.D. Le and R.E. Withler

Abstract

The purpose of this study was to describe population structure and to determine the potential for genetic stock identification of Atlantic cod (Gadus morhua) in Newfoundland and Labrador using microsatellite loci and the synaptophysin (SypI) locus. Variation at seven microsatellite loci (Gmo3, Gmo8, Gmo19, Gmo34, Gmo35, Gmo36, and Gmo37) and SypI was surveyed in approximately 2,700 cod from 13 putative populations. Two populations were sampled over two or more years, and variation among populations was on average about 33 times greater than annual variation within populations. Regional structuring of the populations was apparent with inshore and offshore spawning populations forming distinct groups. The Flemish Cap population was the most distinctive of the offshore group, and the Gilbert's Bay population in Labrador was the most distinctive of the inshore group. In Divisions 2J3KL, no significant genetic differentiation was observed among inshore cod sampling sites in Notre Dame Bay, Trinity Bay, and Bonavista Bay, providing no evidence of distinct "bay" stocks of cod along the northeast coast of Newfoundland. However, cod from the inshore sites were genetically distinct from most offshore samples of northern cod. The offshore samples were more heterogeneous, and there may be at least two distinct offshore spawning populations of northern cod. In Subdiv. 3Ps, genetic differentiation was observed between the inshore Placentia Bay and Fortune Bay samples, and the Placentia Bay sample was generally distinct from offshore samples of northern cod. The Burgeo Bank sample may have been a composite of fish from at least two spawning populations. Simulated mixed-stock fishery samples of northern cod suggested that variation at the seven microsatellite loci and synaptophysin locus should provide reasonably accurate estimates of stock composition (inshore vs. offshore) when the inshore component comprises at least 50% of the mixture. Characters affording greater differentiation among the sampling sites in Subdiv. 3Ps are required to increase the accuracy and precision of the estimated contributions of inshore and offshore cod for practical applications.)

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