Combining microsatellites and geometric morphometrics for the study of redfish (Sebastes spp.) population structure in the Northwest Atlantic

An approach combining genetics and geometric morphometrics has been used to define the population structure of two redfish species, Sebastes mentella, and S. fasciatus, in the northwest Atlantic. The genotype at 13 microsatellite loci, and body shape-defined by 10 anatomical landmarks-were determined on 1091 specimens representing 19 S. fasciatus and 16 S. mentella fishing aggregations from the northwest Atlantic. Two of the samples came from two fjords, the Saguenay and Bonne Bay. A Mantel test performed on the matrices of pairwise genetic and morphometric distances between samples revealed an overall strong concordance between the two data sets, within species. Altogether, the combination of genetic and morphometric data indicated weak but consistent population structure in the Northwest Atlantic. For S. mentella, the results showed that (i) the Gulf of St. Lawrence-Laurentian Channel (GSL-LCH) area comprises a single biological population, with a signature of introgressive hybridization with S. fasciatus, (ii) the Saguenay Fjord harbours a sink population from the GSL-LCH area, and (iii) there are two populations segregated by depth in the Labrador Sea, which are likely connected with the deep-pelagic and shallow-pelagic populations documented for the Irminger Sea. For S. fasciatus, the combined analysis revealed the presence of a highly differentiated population in the Bonne Bay Fjord. The analysis also detected a weak structure at a large geographical scale, between three broad geographical regions, (i) the GSL-LCH area, where there is a signature of introgressive hybridization with S. mentella, (ii) the Gulf of Maine, and (iii) the continental slope from the northern Grand Banks to the mouth of the Laurentian Channel. Population structure of S. fasciatus at a smaller spatial scale is suggested by genetic (in the GSL-LCH area) and morphometric (in the Gulf of Maine) heterogeneity, but warrant further investigations. The implications of the observed population structure for fishery management are discussed.