title: Population structure in Atlantic cod in the eastern North Sea-Skagerrak-Kattegat: early life stage dispersal and adult migration.
abstract: BACKGROUND
  In marine fish species, where pelagic egg and larvae drift with ocean currents, population structure has been suggested to be maintained by larval retention due to hydrographic structuring and by homing of adult fish to natal areas. Whilst natal homing of adults has been demonstrated for anadromous and coral reef fishes, there are few documented examples of philopatric migration in temperate marine fish species.
  
  
  RESULTS
  Here, we demonstrate temporally stable genetic differentiation among spawning populations of Atlantic cod (Gadus morhua L.), and present genetic and behavioural evidence for larval drift and philopatric migration in the eastern North Sea-Skagerrak-Kattegat area. We show that juvenile cod collected in the eastern Skagerrak and central Kattegat are genetically similar to cod from offshore spawning areas in the eastern North Sea. Genetic assignment of individual 2-5 year old fish indicates that cod residing at, or migrating towards, spawning areas in Kattegat and the North Sea display philopatric behaviours.
  
  
  CONCLUSIONS
  Together these findings suggest a loop between spawning, larval drift and adult return-migrations to spawning areas and underlines that both oceanographic processes and migratory behaviour in the adult phase may be important for stock separation and integrity in marine temperate fishes such as Atlantic cod.
authors: Department of Marine Sciences-Tjärnö, University of Gothenburg, 452 96, Strömstad, Sweden. carl.andre@gu.se.
authors: Carl
authors: C
authors: André
authors: Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences, 453 21, Lysekil, Sweden. henrik.svedang@slu.se.
authors: Henrik
authors: H
authors: Svedäng
authors: Institute of Marine Research, Flødevigen, 4817, His, Norway. halvor.knutsen@imr.no.|Department of Biosciences, Centre for Ecological and Evolutionary Synthesis, University of Oslo, P.O. Box 1066, Blindern, 0316, Oslo, Norway. halvor.knutsen@imr.no.|University of Agder, 4604, Kristiansand, Norway. halvor.knutsen@imr.no.
authors: Halvor
authors: H
authors: Knutsen
authors: Institute of Marine Research, PO Box, 1870, 5817, Nordnes, Bergen, Norway. geir.dahle@imr.no.
authors: Geir
authors: G
authors: Dahle
authors: Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences, 453 21, Lysekil, Sweden. patrik.jonsson@slu.se.
authors: Patrik
authors: P
authors: Jonsson
authors: Department of Marine Sciences-Tjärnö, University of Gothenburg, 452 96, Strömstad, Sweden. anna-karin.ring@marine.gu.se.
authors: Anna-Karin
authors: AK
authors: Ring
authors: Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences, 453 21, Lysekil, Sweden. mattias.skold@slu.se.
authors: Mattias
authors: M
authors: Sköld
authors: Department of Biosciences, Centre for Ecological and Evolutionary Synthesis, University of Oslo, P.O. Box 1066, Blindern, 0316, Oslo, Norway. p.e.jorde@ibv.uio.no.
authors: Per Erik
authors: PE
authors: Jorde
mesh_terms: D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal; D048389:Gadus morhua / Q000235:genetics / Q000502:physiology*; D005828:Genetics, Population; D008018:Life Cycle Stages / Q000502:physiology*; D011157:Population Dynamics