Pedersen, Jens Thaulow

Traditionally, marine fish species have been viewed as consisting of single panmitic populations because of obvious lack of physical barriers in the marine environment. Most of the world’s fisheries are now overexploited and sustainable management is warranted. The identification of genetic structure and genetic variation in populations of exploited species is a prerequisite for correct management to secure long term sustainable yield and to protect biodiversity. Resent studies have strongly suggested population structuring of marine fishes down to a micro-geographical scale of a few tens of kilometres supposedly maintained by environmental barriers and adaptation to local environments. These findings illustrate the importance of focusing on local populations for management and conservation of local genetic diversity, which in turn is important for securing long term evolutionary potential in a changing environment. Different molecular markers have been applied over the course of population genetic history to identify these interactions. The possible application and power to detect genetic differentiation between populations varies among molecular markers making the choice of marker, best suited for the study at hand, important. My results strongly indicate that single nucleotide polymorphic markers (SNP) provide more power to detect population admixture among subpopulations with low genetic differentiation, compared to microsatellites. The results suggest the presence of a hybrid zone explained by a hybrid swarm model between the genetically different eastern and western Baltic cod populations in the Baltic Sea. Additionally, the results suggest stability within temporally separated samples from the eastern and western Baltic cod stocks. Further, I most likely identified the most eastern spawning location of the western Baltic cod stock. Last but not least, I identified the genetic identity of spawning mature cod, sampled in the western Baltic in the Arkona basin, as belonging to the eastern Baltic cod population. These findings could have important implications for future assessment and management of the two stocks.Traditionally, marine fish species have been viewed as consisting of single panmitic populations because of obvious lack of physical barriers in the marine environment. Most of the world’s fisheries are now overexploited and sustainable management is warranted. The identification of genetic structure and genetic variation in populations of exploited species is a prerequisite for correct management to secure long term sustainable yield and to protect biodiversity. Resent studies have strongly suggested population structuring of marine fishes down to a micro-geographical scale of a few tens of kilometres supposedly maintained by environmental barriers and adaptation to local environments. These findings illustrate the importance of focusing on local populations for management and conservation of local genetic diversity, which in turn is important for securing long term evolutionary potential in a changing environment. Different molecular markers have been applied over the course of population genetic history to identify these interactions. The possible application and power to detect genetic differentiation between populations varies among molecular markers making the choice of marker, best suited for the study at hand, important. My results strongly indicate that single nucleotide polymorphic markers (SNP) provide more power to detect population admixture among subpopulations with low genetic differentiation, compared to microsatellites. The results suggest the presence of a hybrid zone explained by a hybrid swarm model between the genetically different eastern and western Baltic cod populations in the Baltic Sea. Additionally, the results suggest stability within temporally separated samples from the eastern and western Baltic cod stocks. Further, I most likely identified the most eastern spawning location of the western Baltic cod stock. Last but not least, I identified the genetic identity of spawning mature cod, sampled in the western Baltic in the Arkona basin, as belonging to the eastern Baltic cod population. These findings could have important implications for future assessment and management of the two stocks

Genetic population structure of Atlantic cod (Gadus morhua) in the Baltic Sea

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Roskilde Universitet