Differential Marking of Embryos by Location and Date of Release Reveals Within‐River Natal Homing and Parental Influence on Progeny Return Timing in Sockeye Salmon

Abstract

The tendencies of salmon and trout to spawn in proximity to their natal sites and follow the parental timing of breeding are fundamental to their population structure and also affect the performance of enhancement facilities. Specifically, an understanding of how parental spawning date and offspring release location affect the timing and place of breeding by returning adults is important for the evaluation of hatchery supplementation programs and their integration with sympatric naturally spawning populations. We collected Sockeye Salmon Oncorhynchus nerka carcasses in the Cedar River, Washington, over three spawning seasons to evaluate spawn timing and distribution. Thermal marks on the otoliths of hatchery‐origin carcasses allowed assignment of fish to parents that spawned in the early, middle, and late parts of the season and to fry release locations in the lower, middle, and upper parts of the river. The early portion of the spawning run was composed of a higher proportion of hatchery‐origin fish than was the case later in the season. Hatchery‐origin adults that were released early in the spring as fry (from early spawning parents) were recovered early in the season, and those released later in the spring as fry were recovered later in the season. The natural‐origin spawn timing most closely matched the spawn timing of middle and late hatchery fry release groups in all years. Our data also demonstrated a correspondence between hatchery fry release location and adult recovery location; fry released at river kilometer (rkm) 1.0 were recovered 7.0 km lower (median value) in the river than fry released at rkm 21.7 and were recovered 10.0 km lower than fry released at rkm 35.1. These data contribute to the substantial body of evidence that population characteristics of anadromous salmonids are sensitive to influence from fish culture practices—even under benign regimes—because of the strong connections between parental and progeny timing and the fine‐scale homing of salmon to release sites within a river.

Assortative mating for reproductive timing affects population recruitment and resilience in a quantitative genetic model

“…Assortative mating based on phenotype has been studied in a number of wild fish species, with the majority of examples around the world focused on the evolution of traits such as size (de Borghezan et al, 2019 ; Rios Moura et al, 2021 ; Rueger et al, 2016 ) or color (Utagawa et al, 2016 ). In the North Pacific Ocean, long‐term ecological monitoring studies on salmon (e.g., Barnett et al, 2019 ; Ford et al, 2015 ; Lin et al, 2017 ; May, 2022 ; Peterson et al, 2014 ) have found many cases of spatial and temporal assortative mating. This assortative mating based on temporal (May, 2022 ) or spatial (Lin et al, 2017 ; Peterson et al, 2014 ) variation in spawning behavior suggests that assortative mating in space and time can have positive effects on fitness and population productivity (May, 2022 ).…”

Ontogenetic shifts in olfactory rosette morphology of the sockeye salmon, Oncorhynchus nerka

“…During their adult life stages, they migrate long distances back to their natal stream, relying on odor memories to return to the natal site for spawning, years after they left it as juveniles. Thus, the olfactory system must be sufficiently developed at early juvenile stages to acquire chemosensory information needed for learning (imprinting to) natal stream odors that are used later to guide homing migrations (Barnett et al, 2019 ; Brannon, 1972 ; Quinn et al, 2006 ; Zielinski & Hara, 1988 ).…”

Evidence of an olfactory imprinting window in embryonic Atlantic salmon

“…For example, sockeye salmon, O . nerka , disperse from their natal streams into nursery lakes, where they rear, typically for 1 or 2 years, before the PST and migration to the sea, yet successfully home to the natal tributaries or even specific parts of those tributaries (Barnett et al, 2019; Quinn et al, 2006) rather than the lake outlet they experienced as smolts. Furthermore, juvenile coho, Chinook ( O .…”