Abstract
The effect of extreme floods on the genetic composition of marble trout Salmo marmoratus living in Lipovscek, a tributary of the Soca River in Slovenia, which has been affected by multiple destructive flood events for centuries was investigated. By monitoring genetic variability during the period 2004–2011, apparent signatures of genetic erosion including a decline in observed and expected heterozygosities and allelic richness were observed. Contemporary effective population size was estimated between 11 and 55 individuals, which is congruent with census data. The data suggest asymmetric gene flow between the two sections of the river. The existence of substantial downstream migration (15–19%) was confirmed by paternity analysis. A small (1–3%) upstream migration was also suggested, which was confirmed by tagging data. Overall, low genetic diversity has not prevented the survival of the Lipovscek population, which might be a common feature of salmonid freshwater populations.