Contemporary reproductive patterns of Snake River Oncorhynchus nerka in Pettit Lake

Abstract

Maintaining genetic biodiversity is a focal point for conservation of endangered species. As such, reproductive patterns and behaviors are key to understanding how to aid in species conservation. Snake River Sockeye Salmon (Oncorhynchus nerka) are an endangered species with reproductive complexity created by intermixing life history strategies including: anadromous Sockeye Salmon, residual Sockeye Salmon, kokanee, and introgressed populations. We explore the reproductive behaviors, intermixing life history groups, and resulting juvenile production of Pettit Lake O. nerka using genetic stock identification and parentage-based tagging of outmigrating juveniles and returning or released adults. We also compared how production varied between equal and female-biased sex ratio years of adult releases and used this data to explore a sex ratio that can be used to maximize production for management purposes. In this study, Pettit Lake was found to have consistent intermixing between every known life history group in the lake. We determined that a female-biased sex ratio led to larger females selecting for captive males, more production from residual males spawning with captive females, and increased production of age-1 outmigrants. At higher female-biased sex ratios, we found evidence of males spawning with multiple females and an increase in outmigrant production. Our data supports maximizing production by adopting a captive adult release sex ratio of two females per male in a system limited by available adults. These findings provide further understanding on the complexity of reproductive patterns and demonstrate the importance of monitoring and utilizing scientific findings to maximize conservation efforts and management decisions.