Kokanee–sockeye salmon hybridization leads to intermediate morphology and resident life history: implications for fisheries management

Stocking programs designed to return extirpated species to their historical range have become increasingly prevalent, punctuating the need to better understand the risks posed to recipient ecosystems. Here, we investigated the genetic and biological consequences of an anadromous sockeye salmon (Oncorhynchus nerka) stocking program in Skaha Lake, British Columbia, where substantial levels of hybridization/introgression with the native freshwater resident ecotype (kokanee) have been detected. We genetically-assigned 543 individuals (adult spawners, age-0 juveniles) to estimate stock proportions (pure-stock sockeye/kokanee or hybrid) between 2010 and 2017, with a subset undergoing otolith microchemistry analysis to determine migratory life history and maternal ancestry. Proportion of hybrid spawners varied from 5-20% across sampling years, while hybrid age-0 juveniles remained relatively constant (~11%). Hybrid spawners exhibited intermediate size relative to pure-stocks, with the vast maj...