Data from: Kokanee-sockeye salmon hybridization predominantly leads to a resident life history with outcomes for a long-term reintroduction program

Stocking programs have been widely implemented to restore extirpated fish
species to their historical ranges, and must include careful consideration
of potential hybridization dynamics. The sockeye salmon (Oncorhynchus
nerka) reintroduction project in Skaha Lake (British Columbia, Canada)
provides an excellent opportunity to investigate the outcomes of
hybridization between anadromous (migratory) sockeye and resident kokanee
over a two-decade long program. Prior research established the presence of
hybrids, with the vast majority of F1 spawners exhibiting a resident life
history. Yet, it remains unknown whether anadromous hybrid smolts exhibit
fitness effects in the form of reduced survival during migration, or
whether they predominantly remain resident. Here, we paired cohort-based
sampling (age-0 fry, age-1 smolts, adult spawners) in Skaha Lake with SNP
genotyping, otolith microchemistry, and morphometrics to: 1) reconstruct
trends in stock proportions of sockeye, kokanee and hybrids (F1,
B1-sockeye, B1-kokanee) over a 15-year time series; and 2) investigate the
morphological, behavioral and fitness outcomes of sockeye-kokanee
hybridization. Genetic assignments revealed stock proportions varied
widely over time and across cohorts, with hybrids making up a substantial
proportion of the population despite earlier suggestions that hybrids may
exhibit reduced fitness. Approximately 94% of F1 and 100% of B1-kokanee
spawners exhibited microchemical evidence of a resident life history.
Conversely, B1-sockeye spawners were evenly split between resident and
anadromous, displaying a significant difference in fork length associated
with life history and providing further evidence for a genetic basis to
migratory behaviour. More broadly, our findings have important management
implications for habitat restoration and underscore the need for continued
monitoring with consistent sampling among partner organizations.