Multiple paternity increases effective size of southern Atlantic salmon populations

Genetic analyses were performed on the progeny of Atlantic salmon (Salmo sa lar L.) sampled in natural redds of three rivers flowing into the Bay of Bi scay, the Nivelle, the Mandeo and the Sella. These rivers are at the southe rn limit of the European distribution of the species and their populations are small and endangered by human activities. Nine variable number of tande m repeat (VNTR) loci (five minisatellites and four microsatellites) were us ed for parentage analysis. Multiple male participation was recognized in th e fertilization of eggs. A large proportion was fertilized by precociously mature parr. We demonstrate that multiple paternity derived from mature par r is crucial for the conservation of genetic variability in small populatio ns of Atlantic salmon.