Single-parentage analysis of Sockeye Salmon

Understanding reproductive patterns in endangered species is critical for
supporting their recovery efforts. In this study we use a combination of
paired-parent and single-parent assignments to examine the reproductive
patterns in an endangered population of sockeye salmon (Oncorhynchus
nerka) that uses Redfish Lake in central Idaho as a spawning and nursery
lake. Recovery efforts include the release of maturing adults into the
lake for volitional spawning. The lake is also inhabited by a population
of resident O. nerka that is genetically indistinguishable, but
phenotypically smaller, to the maturing adults released into the lake. The
resident population is difficult to sample and the reproductive patterns
between the two groups are unknown. We used results of paired- and
single-parentage assignments to specifically examine the reproductive
patterns of male fish released into the lake under an equal sex ratio and
a male-biased sex ratio. Assignment results of offspring leaving the lake
indicated a reproductive shift by males under the two scenarios. Males
displayed an assortative mating pattern under an equal sex ratio and
spawned almost exclusively with the released females. Under a male-biased
sex ratio most males shifted to a negative-assortative mating pattern and
spawned with smaller females from the resident population. These males
were younger and smaller than males that spawned with released females
suggesting they were unable to compete with larger males for spawning
opportunities with the larger, released females. The results provided
insights into the reproductive behavior of this endangered population and
has implications for recovery efforts.