The influence of family-correlated survival onNb/Nfor progeny from integrated multi- and single-generation hatchery stocks of coho salmon (Oncorhynchus kisutch)

Abstract

There exist surprisingly few data on the final variance and mean of family sizes for hatchery-born fish at the adult stage. Thus, it is difficult to predict, for a conservation hatchery operation that minimizes the variance in progeny number, how much lower the true effective population size (Ne) of a cohort of hatchery-born adults will be than Nepredicted simply by the number of parents that produced them. We used parentage analysis to estimate the survival and Nefor two integrated stocks of hatchery coho salmon (Oncorhynchus kisutch). One hatchery is a multigeneration stock obtained by spawning 70% hatchery with 30% naturally reproducing fish, whereas the second is a single-generation stock derived from naturally reproducing coho. There was no significant difference in average overall survival between stocks, but observed Newas significantly less than expected for each stock. Family-correlated survival contributed to roughly a 20% reduction in Neover the freshwater and marine life stages. This reduction is similar to previous estimates and suggests a value that can be used when estimating the effective number of hatchery parents in applications of the Ryman–Laikre formula (at least for programs such as ours that attempt to equalize sex ratios and family sizes).