Long-term monitoring of a brown trout (Salmo trutta) population reveals kin-associated migration patterns and contributions by resident trout to the anadromous run

Abstract Background In species showing partial migration, as is the case for many salmonid fishes, it important to assess how anthropogenic pressure experienced by migrating individuals affects total population. We focused on brown trout ( Salmo trutta ) from Guddal River in Norwegian Hardanger Fjord system, which encompasses both resident and anadromous individuals. Aquaculture has led increased during marine phase this region. Fish traps allow sampling all ascending spawners descending smolts. analyzed microsatellite DNA markers 2006–2016, along with emigrating smolts 2017. investigated (1) if there was evidence declines census numbers effective population size that period, (2) association between kinship migration timing adults, (3) what extent were parents of outmigrating Results Census counts showed no a decline 2006 2016, but lower than 2000–2005. Estimates also trends study period. Sibship reconstruction 2017 smolt run significant timing, similar indicated spawners. Parentage assignment candidate parents, assuming unknown represented trout, 70% had at least one parent 24% two parents. Conclusions The results bear after an initial stabilized number suggests specific episodes elevated mortality sea could disproportionally affect some families reduce overall size. Finally, based parentage demonstrate strong buffering effect affecting highlight most are females, may production system.