Changing Growth and Maturity in Western Alaskan Chinook Salmon, Oncorhynchus tshawytscha, Brood Years 1975–2005

McPhee, Megan V.; Leon, Justin; Wilson, Lorna Rachel Maven; Siegel, Jared; Agler, Beverly A.

doi:10.23849/npafcb6/307-327

Cited by 6 publications

(6 citation statements)

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“…2a). This finding generalizes previous species-and region-specific analyses 19,30,31 . Size trends were more similar for a given species across regions than for a given region across species (Fig.…”

Section: Discussionsupporting

confidence: 90%

“…Chinook salmon, which exhibit the greatest life history diversity and thus greatest capacity for change in age-at-maturity, showed the greatest magnitude of decline in both body size and age-at-maturity. This result formalizes and extends findings from previous studies that age truncation appears to play an important role in declining Chinook salmon body size 19,30,31,33 . Compared to Chinook salmon, changes in age-at-maturity were more variable through time in chum and sockeye salmon ( Fig.…”

Section: Discussionsupporting

confidence: 89%

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Recent declines in salmon body size impact ecosystems and fisheries

et al. 2020

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Declines in animal body sizes are widely reported and likely impact ecological interactions and ecosystem services. For harvested species subject to multiple stressors, limited understanding of the causes and consequences of size declines impedes prediction, prevention, and mitigation. We highlight widespread declines in Pacific salmon size based on 60 years of measurements from 12.5 million fish across Alaska, the last largely pristine North American salmon-producing region. Declines in salmon size, primarily resulting from shifting age structure, are associated with climate and competition at sea. Compared to salmon maturing before 1990, the reduced size of adult salmon after 2010 has potentially resulted in substantial losses to ecosystems and people; for Chinook salmon we estimated average per-fish reductions in egg production (−16%), nutrient transport (−28%), fisheries value (−21%), and meals for rural people (−26%). Downsizing of organisms is a global concern, and current trends may pose substantial risks for nature and people.

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Section: Discussionsupporting

confidence: 90%

Section: Discussionsupporting

confidence: 89%

Recent declines in salmon body size impact ecosystems and fisheries

et al. 2020

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“…The availability of 10 recaptured PIT‐tagged individuals allowed us to validate saltwater age in steelhead in the Situk River, and the use of mixed‐effects models allowed us to maximize the information that we obtained from the individual fish while accounting for the correlations among individuals from the same growth year (see also McPhee et al. ; Debertin et al. ).…”

Section: Discussionmentioning

confidence: 99%

“…Calendar year of growth rather than brood year was included as a random term to account for correlations among individuals that were growing at the same time (e.g., McPhee et al. ). Smolt year (first spring/summer at sea) was used to index this cohort effect due to the uncertainty in assigning freshwater age.…”

Section: Methodsmentioning

confidence: 99%

Interactions between Marine Growth and Life History Diversity of Steelhead from the Situk River, Alaska

Catterson

Sutton

McPhee

2020

N American J Fish Manag

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Steelhead (the anadromous form of Rainbow Trout Oncorhynchus mykiss) exhibit a complex life history that is described by variable freshwater and ocean residency and maturation schedules. This diversity confers resilience but complicates their monitoring and management. The Situk River in Southeast Alaska has the longest running set of biological data and scale samples for steelhead in the state, and it is of particular interest because it supports the largest known population of steelhead in Alaska and is free of hatchery influence. We used a retrospective analysis of scales that were collected from 525 individuals over 11 years (1999–2012) to examine the relationships among freshwater growth, early ocean growth, and life history in a mixed‐effects modeling framework. Specifically, we examined the relationships among annual growth stanzas and adult length and we determined how age at maturity varied by sex and growth history while allowing these relationships to vary randomly among calendar years of growth. Within individuals, freshwater and first ocean‐year growth were positively correlated, while second ocean‐year growth was negatively correlated with earlier growth stanzas. Early‐maturing steelhead (returning after two ocean years) grew more quickly during their first ocean year, and they then grew more slowly during their second ocean year and attained smaller adult length than did later‐maturing steelhead (those that returned after three ocean years). Second ocean‐year growth was more variable than first ocean‐year growth and adult length were. Males tended to mature earlier than females did, and later‐maturing males attained larger freshwater growth than their earlier‐maturing male counterparts did and grew larger in overall length than did females. Our analyses identified divergent growth trajectories that were associated with age at maturity that began in freshwater periods but were most pronounced during early ocean residency. We found retrospective scale‐growth analysis to be a useful tool for better understanding the connections between ocean growth and demography in this important sport fish.

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“…A similar study failed to find a single cause of declining ocean age structure and size and instead determined that multiple anthropogenic and environmental changes were likely contributing (McPhee et al. ).…”

Section: Discussionmentioning

confidence: 99%

Examining Life History Shifts and Genetic Composition in a Hatchery Steelhead Population, with Implications for Fishery and Ocean Selection

et al. 2019

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Steelhead Oncorhynchus mykiss exhibit significant variation in life histories. Dworshak National Fish Hatchery (NFH)‐stock steelhead exhibit a life history that is unique compared to other Columbia River basin hatchery summer steelhead stocks, as it is dominated by older and larger‐length fish relative to conspecifics. We evaluated changes within the Dworshak NFH stock's ocean age composition and length at age from run years 1978 to 2016 using samples collected from the commercial gill‐net fishery, the sport fishery, and the hatchery trap. In addition, we analyzed the genetic composition of the stock by comparing samples collected in 1969 from the wild founding stock to samples from recent returns. We found that Dworshak NFH steelhead became younger across the study, with fewer of the oldest, three‐ocean fish (i.e., rearing in the ocean for 3 years) and increases in the proportion of the population returning as one‐ocean fish (i.e., rearing in the ocean for 1 year). Length at ocean age decreased for all ocean ages; however, the decrease was not significant in one‐ocean fish. In general, samples collected from gill nets and the sport fishery contained fish with older ocean ages and larger sizes at age compared to samples collected from the hatchery trap. Neutral genetic diversity, as measured from a panel of single‐nucleotide polymorphic markers, showed no changes between the sample of fish representing the original founders and the present‐day population. Life history shifts observed in Dworshak NFH‐stock steelhead were likely influenced by a variety of factors, including gear selectivity and changing ocean conditions. Decreases in ocean age composition and length at age have implications for both fishery and broodstock management as well as generating concern that similar trends may be occurring within wild steelhead stocks.

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Changing Growth and Maturity in Western Alaskan Chinook Salmon, Oncorhynchus tshawytscha, Brood Years 1975–2005

Cited by 6 publications

References 0 publications

Recent declines in salmon body size impact ecosystems and fisheries

Recent declines in salmon body size impact ecosystems and fisheries

Interactions between Marine Growth and Life History Diversity of Steelhead from the Situk River, Alaska

Examining Life History Shifts and Genetic Composition in a Hatchery Steelhead Population, with Implications for Fishery and Ocean Selection

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