Larval group differentiation in Atlantic cod (Gadus morhua) inside and outside the Gullmar Fjord |
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Authors: | Vidar
resland Carl Andr |
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Institution: | aInstitute of Marine Research, Swedish Board of Fisheries, P.O. Box 4, SE-453 21 Lysekil, Sweden bDepartment of Marine Ecology, Göteborg University, Tjärnö Marine Biological Laboratory, SE-452 96 Strömstad, Sweden |
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Abstract: | The spatial and temporal occurrence of pelagic fish stages and their biological variability may affect their dispersal and survival, and ultimately fish recruitment. We collected Atlantic cod larvae at one station inside and at one station outside the Gullmar Fjord, eastern Skagerrak, in order to investigate small-scale larval group differentiation. Rectangular midwater trawl hauls were taken every 6 h (during 24 h) from three separate depth intervals between the surface and 70 m depth. About 80% and 20% of all larvae occurred above the halocline at the Fjord station and the Coastal station, respectively. Hatching (at both stations) occurred from the 3rd week in February to the 1st week in May, indicating that cod larvae were present for at least 5 months (from late February to early August). The length and hatch date frequency distributions of larvae from the surface layer were unimodal inside the fjord but bimodal outside the fjord. Analyses of seven microsatellite DNA loci indicated that larvae collected inside the fjord (where local spawning occurs) were genetically distinct from larvae sampled on the outside (FST = 0.0026). The two age cohorts outside the fjord were not, however, genetically different, nor were larvae collected at different depths. We conclude that small-scale variability of vertical concentration and larval life history variability should have consequences for interpreting models of larval dispersal and survival, and subpopulation structure analyses. |
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Keywords: | Cod Gadus morhua Larvae Spawning Hatch dates Genetic Otoliths Vertical distribution Dispersal |
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