Evaluating a multi-generational reintroduction program for threatened salmon using genetic parentage analysis

Abstract

Dams, utilized for hydroelectric or flood control purposes, obstruct organism dispersal and have contributed to the decline of many migratory fish populations. For threatened Chinook salmon (Oncorhynchus tshawytscha) from the Willamette River Basin in Oregon, human-assisted reintroductions are being used to facilitate dispersal to historical habitats located above dams. However, little is known about the reproductive outcomes of reintroduced individuals or the efficacy of reintroductions towards the goal of population demographic viability. Using genetic parentage assignments to 3-, 4-, and 5-year-old adult recruits, we estimated the fitness of hatchery and wild Chinook salmon reintroduced above Foster Dam on the South Santiam River, a tributary of the Willamette River. Our parentage assignments indicated that the fitness of reintroduced salmon was highly variable, with individuals producing a range of 0–40 adult progeny. We also detected a possible trend towards reduced fitness in mate pairs composed of hatchery versus wild salmon. For each of three brood years (2007, 2008, 2009), adult offspring recruitment achieved or exceeded population replacement. We observed the highest cohort replacement rate in 2009, the first year that managers aimed to release wild salmon solely above the dam. Taken together, our results suggest that human-assisted reintroductions of mature adult salmon to historical spawning habitats are a promising method of restoring natural production in populations affected by dams. Moreover, the continued used of wild fish in reintroduction operations may improve population productivity and the prospect of recovery within the South Santiam River.

Grandparentage assignments identify unexpected adfluvial life history tactic contributing offspring to a reintroduced population

“…This trap and transport reintroduction approach has enabled the near complete tissue sampling of all the potential anadromous adult parents, thereby allowing for estimates of CRR. Contrary to recently published studies for other Chinook and coho (O. kisutch) salmon reintroductions (Anderson et al 2015;Evans et al 2015), current CRR estimates suggest that the population above Cougar Dam is not replacing itself (Sard et al 2016).…”

“…The observed increases in CRR were not enough to meet replacement for either the 2007 or 2008 cohorts. Even with the incorporation of adfluvial Chinook salmon offspring, CRR for adults reintroduced above Cougar Dam are low compared to other published studies (Anderson et al 2015;Evans et al 2015). However, just as in parentage assignments, grandparentage methods are limited by genotyping error and further exacerbated by our conservative exclusion criterion, which could negatively bias our estimates.…”

“…; Evans et al. ). However, just as in parentage assignments, grandparentage methods are limited by genotyping error and further exacerbated by our conservative exclusion criterion, which could negatively bias our estimates.…”

“…; Evans et al. ), current CRR estimates suggest that the population above Cougar Dam is not replacing itself (Sard et al. ).…”

Coho Salmon Colonization of Oregon's Upper Willamette River Basin

“…The near-complete failure of colonization in several other stocked UWR tributaries (e.g., Luckiamute, Marys, and Coast Fork Willamette rivers) has been attributed to a variety of constraints. These river basins have lower relief, little spring snowpack, and lower and warmer summer baseflows than the successfully colonized UWR tributaries and consequently have little high-quality habitat for Coho Salmon spawning and rearing (Myers et al 2003;NMFS 2008 Keefer et al 2010;Evans et al 2016).…”