Diminished Reproductive Success of Steelhead from a Hatchery Supplementation Program (Little Sheep Creek, Imnaha Basin, Oregon)

Abstract

Hatchery supplementation programs are designed to enhance natural production and maintain the fitness of the target population; however, it can be difficult to evaluate the success of these programs. Key to the success of such programs is a relatively high reproductive success of hatchery fish. This study investigated the relative reproductive success (RRS) of steelhead Oncorhynchus mykiss (anadromous rainbow trout) by creating pedigrees for hatchery and natural spawning steelhead. We genotyped adult steelhead that returned to a weir and were released upstream to spawn in Little Sheep Creek, a tributary to the Imnaha River in eastern Oregon. The broodstock for this supplementation program were originally chosen from natural‐origin steelhead returning to the weir and in subsequent years consisted of both natural‐ and hatchery‐origin individuals. Microsatellite analyses showed the broodstock to be genetically similar to the natural population across years. We also genotyped adult resident rainbow trout from multiple locations upstream of the weir and determined the parentage of progeny collected at various life history stages, including returning adults in subsequent years. Analysis of progeny sampled at both the juvenile and adult life stages suggested that the RRS of hatchery‐origin fish was 30–60% that of their natural‐origin counterparts. Using generalized linear models to address the importance of various factors associated with reduced reproductive success, we found that the greatest effects on RRS were origin (natural versus hatchery), length, return date, and the number of same‐sex competitors. Natural parents were less negatively affected by same‐sex competitors. Differential survival of juveniles and the behavior of offspring and/or spawning adults may all contribute to diminished fitness in hatchery‐reared salmon, although it could not be determined to what extent these effects were of a persistent, heritable nature as distinct from an environmental effect associated with hatchery rearing and release strategies.

Evaluating Adaptive Divergence Between Migratory and Nonmigratory Ecotypes of a Salmonid Fish, Oncorhynchus mykiss

“…They found that migrant offspring produced by migrant fish had a greater proportion of returns than migrant offspring from resident fish, suggesting migrants are inheriting alleles that promote ocean survivability. In contrast, the Little Sheep Creek samples were collected from an area where migratory and resident life history types coexist providing greater opportunity for mating between the life history types (Berntson et al 2011) as confirmed by the few loci associated with migration/residency, few F ST outliers, low levels of LD, largely neutral Tajima’s D values, and low numbers of private alleles. Similar low levels of F ST and few outliers are found in other populations of O. mykiss where residents and migrants co-occur (Limborg et al 2012).…”

“…All migrants sampled were downstream of these waterfalls, whereas all residents sampled were upstream (see Thrower et al 2004 for more details). The migrant and resident individuals in the Little Sheep Creek population are not separated by barrier waterfalls (see Berntson et al 2011 for more details) and so samples of both phenotypes were taken from the same area. Resident trout from the Little Sheep Creek, Oregon, population were determined to be resident as determined by size threshold (minimum fork length of 160 mm).…”

Developing a broader scientific foundation for river restoration: Columbia River food webs

“…Examining the Columbia River restoration program, in light of river restoration in general, provides insights into factors underpinning successful activities (e.g., improved survival at dams for juvenile salmonids) (34) as well as less successful efforts (35). The Northwest Power and Conservation Council (NPCC) Fish and Wildlife Program for the Columbia River seeks to establish and maintain an ecosystem that sustains an abundant, productive, and diverse community of fish and wildlife (36).…”

Release of hatchery adult steelhead for angler opportunity increases potential for interactions with endemic steelhead

“…One management action is recycling, where collected adults are released back to fisheries for additional angling opportunity (Lindsay et al 2001, Kock et al 2016. However, any SRS not harvested or recollected could increase competition for mates on spawning grounds, spawn with other hatchery-produced fish, or hybridize with endemic conspecifics locally or after straying to other basins (Araki et al 2007, Berntson et al 2011. However, any SRS not harvested or recollected could increase competition for mates on spawning grounds, spawn with other hatchery-produced fish, or hybridize with endemic conspecifics locally or after straying to other basins (Araki et al 2007, Berntson et al 2011.…”