No indications of Atlantic salmon (Salmo salar) shoaling with kin in the Baltic Sea

Several studies have shown that fish shoals may consist of closely related individuals. It has been found. for example, that released out-migrating salmon smolts tend to aggregate with kin. including when sibling groups have been reared separately. We used genetic microsatellite markers to test whether "shoals" of adult Atlantic salmon (Salmo salar) during the marine phase (i.e., aggregations of fish Caught in drift nets at offshore feeding areas in the Baltic Sea) consisted of closely related individuals (full-siblings, half-siblings). We found no evidence of kin cohesiveness related to shoals, however. Despite a weak overall tendency for individuals assigned to the same population (river or stock) to Occur tooether, estimates of genetic relatedness in combination with consistent heterozygote deficiencies. and results from mixed-stock analyses and assignment tests collectively indicated that shoals consisted of unrelated fish from multiple populations.