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Genetic baseline for conservation and management of sea trout in the northern Baltic Sea

Östergren, Johan, Nilsson, Jan, Lundqvist, Hans, Dannewitz, Johan, Palm, Stefan
Conservation genetics 2016 v.17 no.1 pp. 177-191
Salmo trutta, coasts, fisheries, genes, microsatellite repeats, rearing, trout, watersheds, Baltic Sea
The genetic structure of nine wild, seven hatchery-reared, and one presumably mixed, sea trout (Salmo trutta L.) populations sampled from watersheds along the Swedish Baltic Sea coast was analysed using ten microsatellite loci. DNA-information was evaluated as a baseline for mixed stock analysis (MSA) and individual assignment (IA). A clear genetic structure with distinct populations was identified (global F ST = 0.066), with significant regional differentiation. Average gene diversity (H ₑ) was similar among samples of wild and reared trout, whereas levels of heterozygote deficiency differed significantly (wild: H ₑ = 0.70, F IS = 0.075; reared: H ₑ = 0.69, F IS = 0.022). The high F IS found in wild samples indicates presence of within-river sub-structuring. Evaluation with realistic-fishery simulations indicated that the baseline resolution was sufficient for MSA, at least at a regional level. Hierarchical MSA and IA analyses of real catches from two coastal fisheries showed that populations from the northern region contributed about 90 % to the catch. Analysed individually, the two fisheries differed in catch compositions despite a short geographic distance among sites. One fishery mainly caught sea trout from a small wild population whereas the other fishery was dominated by reared sea trout. Stock composition analysis is a valuable tool for refining exploitation rate estimates for individual sea trout populations in mixed coastal fisheries, as well as for investigating migration patterns in the Baltic Sea.