Consequences of Emergence Timing for the Growth and Relative Survival of Steelhead Fry from Naturally Spawning Wild and Hatchery Parents

Abstract

For many fishes, reproducing early in the year may present tradeoffs for the offspring: the drawbacks associated with harsh environmental conditions may be offset by advantages in competition for food and space. We investigated this tradeoff in a system where hatchery-origin steelhead Oncorhynchus mykiss were bred to spawn about 4 months earlier than wild-origin fish. Hatchery-origin adults were released into the wild and spawned in common with wild steelhead. Naturally spawned offspring from these matings were assigned to hatchery, wild, and hybrid lineages by using a panel of 96 single-nucleotide polymorphisms. We then evaluated whether fry abundance, body size and condition, and geographic distribution differed based on parental lineage. The observed mixture proportions were 0.007 hatchery-lineage, 0.289 hybrid, and 0.704 wild-lineage juveniles, despite the predominance of hatchery-origin parents. There were significant differences in FL (hatchery > hybrid > wild) but no difference in body condition. We modeled the emergence dates of the sampled fry and estimated that 96.0% of wild-lineage fish emerged after the arrival of temperate spring conditions (reduced flows and warmer temperatures) compared with 80.4% of hybrids and 41.2% of hatchery-lineage fish. We hypothesize that the low abundance of pure hatchery-lineage fry may be due to a mismatch between the timing of breeding by the parents and suitable river conditions, resulting in low survival and physical displacement of hatchery-lineage fry from the system. Thus, the advantages of early emergence and large size associated with hatchery origin did not mitigate the disadvantages of early spawning in this case.

Introgressive hybridization between native and non‐local steelhead (Oncorhynchus mykiss) of hatchery origin

“…The timing of adult migration is a heritable trait in salmonids, and has substantial fitness consequences if not synchronized with local environmental conditions (Flagg, Waknitz, Maynard, Milner, & Mahnken, ; Hess, Zendt, Matala, & Narum, ; Jones et al, ; McLean, Bentzen, & Quinn, ; Quinn, Peterson, Gallucci, Hershberger, & Brannon, ). Few natural‐origin summer steelhead were detected in the population, and lower numbers of putative hybrids were backcrossed to the hatchery summer steelhead, despite high abundances of hatchery summer steelhead in the population during reproduction.…”

“…Few natural‐origin summer steelhead were detected in the population, and lower numbers of putative hybrids were backcrossed to the hatchery summer steelhead, despite high abundances of hatchery summer steelhead in the population during reproduction. Jones et al () found similar proportions of hatchery, hybrid, and wild steelhead in a stream in south‐west Washington (1% natural‐origin, hatchery‐lineage steelhead and 29% hybrids), and concluded that the earlier‐spawning hatchery steelhead were emerging during unfavourable conditions; however, the later‐emerging hatchery steelhead were more likely to encounter better environmental conditions for early rearing, resulting in selection for this later migration timing that is more similar to the native population.…”

Contrasting genetic metrics and patterns among naturalized rainbow trout (Oncorhynchus mykiss) in two Patagonian lakes differentially impacted by trout aquaculture

“…Genomic DNA was isolated using a NucleoSpin ® (Macherey-Nagel) kit following the manufacturer's instructions. We amplified 96 SNPs (Table S1) that yielded polymorphic multilocus genotypes in both native (Jones et al, 2015) and naturalized rainbow trout populations (Benavente et al, 2015) (Table S2). Multiplex PCR was carried out using Fluidigm ® 96.96 dynamic array chips following Seeb, Pascal, Ramakrishnan, and Seeb (2009) and procedures of Smith et al (2011) for a pre-amplification step to increase PCR copies under low template DNA concentration.…”

Population, habitat, and marine location effects on early marine survival and behavior of Puget Sound steelhead smolts

“…Substantial releases of hatchery-origin salmonids influence natural populations through ecological mechanisms in both freshwater and marine environments (Naish et al 2008, Rand et al 2012. Interbreeding with hatchery stocks can shift natural population trait distribution by producing offspring with traits intermediate between parental populations (Seamons et al 2012, Jones et al 2015, potentially resulting in reduced survival (Araki et al 2009). Over several generations, phenotypic traits of a natural population can be largely replaced by those of a hatchery population (Ford et al 2006).…”