Understanding Life History Diversity of a Wild Steelhead Population and Managing for Resiliency

Abstract

Diversity in steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) is often characterized by varying time spent in freshwater and saltwater environments. However, ontogenetic shifts are not often highlighted as an important diversity characteristic in salmonids. Larger water bodies can play a key role in population stability by buffering limited resources in smaller tributary systems. Based on freshwater and saltwater ages of adult steelhead in Fish Creek, Idaho, there were 12 different life history trajectories observed. Juvenile abundance varied from 12,083 (SE = 1,225.7) to 62,463 (SE = 1,753.8), with ages ranging from young of the year (age 0) to 4 years. Adult abundance fluctuated from 17 (SE < 0.1) to 499 (SE = 67.1), and total age of adults varied from 3 to 7 years. Diversity was most evident in juvenile movement and rearing strategies. We observed four types of movement and rearing pathways in which juveniles either directly migrated to the ocean from Fish Creek or resided for up to three winters in main-stem river habitat in the Clearwater River basin prior to ocean migration. Most juveniles emigrated in the fall at age 2, and most ocean-emigrating smolts were age 3. Subsequently, most juveniles resided for at least one additional winter period before ocean migration. Juvenile diversity was also reflected in adult ages; the mean proportion that spent 3 years in freshwater was 0.55 (SE = 0.03), and the mean proportion that spent 2 years in freshwater was 0.41 (SE = 0.03). Adult sex ratio was female biased (mean ± SE = 0.66 ± 0.02), with a higher proportion of females (0.89 ± 0.03) than males (0.65 ± 0.05) residing in the ocean for at least 2 years. Density-dependent mechanisms were evident in juvenile rearing habitat in Fish Creek for cohorts of high female abundance. Population productivity potentials can be met when tributary and main-stem rearing habitat can be utilized, and this will be essential in attaining recovery goals.

Evaluation of Management Strategies for an Incidental Catch‐and‐Release Steelhead Fishery

“…For instance, the model assumed that no spawners spent 3 years in the ocean, there were no repeat spawners, no steelhead residualized, and no resident O. mykiss contributed to steelhead production in Fish Creek. All of these life histories have been observed in Fish Creek steelhead or in other interior Columbia River steelhead populations (Kendall et al 2015;Copeland et al 2017Copeland et al , 2019Dobos et al 2020), and all likely contribute to potential resilience of the population. Spawners that spent 3 years in the ocean and repeat spawners were not included in the model to reduce the number of parameters and due to the relatively low number of steelhead that have been observed exhibiting these life histories at the Fish Creek weir.…”

“…Spawners that spent 3 years in the ocean and repeat spawners were not included in the model to reduce the number of parameters and due to the relatively low number of steelhead that have been observed exhibiting these life histories at the Fish Creek weir. For instance, Dobos et al (2020) noted that only 9 of 3,010 spawning steelhead captured at the Fish Creek weir that were aged spent 3 years in the ocean. In addition, only 3 of these 3,010 fish were repeat spawners.…”

Validation of Scale‐Derived Ages in Wild Juvenile and Adult Steelhead Using Parental‐Based Tagging

“…Many wild steelhead in the Snake River basin are tagged with PIT tags as out‐migrating smolts (e.g., Dobos et al. 2020). Scales and fin clips are collected from returning adults as they are passed above weirs.…”

“…Suitable tags may be physical objects, like a coded wire tag inserted into the body of a fish, or physiological marks, like thermal tags on otoliths created by manipulating the environment (Volk et al 1999). Many wild steelhead in the Snake River basin are tagged with PIT tags as out-migrating smolts (e.g., Dobos et al 2020). Scales and fin clips are collected from returning adults as they are passed above weirs.…”

Relationship between Thermal Variance and Hatchery Estimates of Fertility in a Multispecies Assemblage of Anadromous Salmonids in Response to Managed Flows

“…This may be that steelhead initiates spawning in late winter when the thermal regime is at its coldest before transitioning to warmer temperatures through the early fall spawning season. We suggest that a positive regression between fertility with increasing water temperature in steelhead is an expression of a diverse life history portfolio in which not all individuals are "genetically pre-programed to die" after spawning (semelparous) unlike salmon [65,66]. This evolved adaptation in steelhead may contribute to the species' resiliency and persistence despite anthropogenic effects and environmental variability potentially affecting growth and survival [67][68][69][70][71].…”