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Conserving genetic diversity in animal populations is important for sustaining their ability to respond to environmental change. However, the “between-population” component of genetic diversity (biocomplexity) is threatened in many exploited populations, particularly marine fish, where harvest management regions may be larger than the spatial extent of genetically distinct subpopulations. Using single-nucleotide polymorphism data, we delineated the geographic limits of three population units of Atlantic cod (Gadus morhua) in northwest European waters. Two of the populations cohabit the North Sea, and trawl survey data showed differing trends in their abundances. We developed a spatial model of these units to simulate population dynamics under spatial patterns of harvesting. Competition between units during the pelagic juvenile stages in the model led to suppression of the more localized northern North Sea (Viking) unit by the more widespread (Dogger) unit, and its premature extinction under some spatial patterns of fishing. Fishery catch limits for cod are set at the scale of the whole North Sea without regard to such subpopulation dynamics. Our model offers a method to quantify adjustments to regional fishing mortality rates to strike a balance between maximizing sustainable yield and conserving vulnerable populations. [ABSTRACT FROM PUBLISHER]

Salmon from geographically representative rivers in North America and Europe were typed for variation at the microsatellite locus SS1 and the mitochondrial DNA ND-1 restriction site 3971, using PCR amplification and agarose-gel electrophoresis. North American salmon showed near-fixation for SS1 alleles between 129 and 135bp in length and the N mtDNA restriction type, while European salmon near-fixation for SS1 alleles between 183 and 219bp and the A/D mtDNA type. Based on the observed variant frequencies, using these two markers in combination is predicted to give correct assignment of >99.5% of salmon to continent-of-origin. As both these continental markers can be screened by agarose-gel electrophoresis, their use offers a more rapid, cheaper, and simpler method for accurate assignment of Atlantic salmon to continent-of-origin than do existing methods. These markers can be applied to the identification of salmon in North Atlantic high-seas fisheries, in aquaculture stocks, and in rivers to determine the continent-of-origin of fish-farm escapes. [Copyright &y& Elsevier]