Post-Release Performance of Natural and Hatchery Subyearling Fall Chinook Salmon in the Snake and Clearwater Rivers.

Connor, William P.

doi:10.2172/948112

Cited by 1 publication

(1 citation statement)

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“…The total mass of SDN lost from the system owing to growth and subsequent emigration of these hatchery-origin age-0 Chinook salmon from the SRF Chinook salmon ESU was calculated by multiplying mean accrued mass per fish in that year by the number of hatchery-origin age-0 individuals that passed LGD in the fall and the fraction of total juvenile Chinook biomass that is either N or P. We used age-0 summer survival estimates from FPC reports and initial stocking densities to estimate the number of age-0 hatchery-origin fish that migrated in the fall. We assumed a 41% increase in smolt biomass between stocking and out-migration based on data from Connor et al (2008). Chinook salmon eggs are rarely out-planted so we did not include hatchery-origin eggs in this mass balance study as was done in Nislow et al (2004).…”

Section: Methodsmentioning

confidence: 99%

Quantifying Salmon‐Derived Nutrient Loads from the Mortality of Hatchery‐Origin Juvenile Chinook Salmon in the Snake River Basin

Warren

McClure

2012

Trans Am Fish Soc

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Hatchery supplementation of anadromous salmon is extensive across the Pacific Northwest region with millions of juvenile salmon stocked annually. The influence of hatchery‐origin fish as prey items in recipient ecosystems has been explored, but influences of these fish on broader stream nutrient dynamics has not been well‐studied. Salmon‐derived nutrients (SDN) associated with the mortality of adult anadromous salmon provide key subsidies to freshwater habitats. While a number of studies have estimated current and historic SDN loading from returning wild salmon, SDN contributions from the mortality of hatchery‐origin juveniles (many of which die in the stream prior to emigration) remains largely unknown. We conducted a mass balance analysis of SDN input and export via hatchery activities (stocking and broodstock collection) in the Snake River watershed. Using Chinook salmon Oncorhynchus tshawytscha as a model species, we accounted for yearly SDN input (via hatchery‐origin juvenile fish mortality) and export (via broodstock collections and presmolt growth) over 6 years (2002–2007) in the portion of the Snake River upstream from Lower Granite Dam accessible to anadromous fish. In the year with highest smolt mortality (2003), hatchery‐origin smolt mortality provided a net input of SDN equivalent to approximately 8,100 returning adults. In the year with lowest smolt mortality (2004), hatchery activities collectively yielded a net loss of nutrients. Although the mass of SDN from hatchery‐origin smolts may be presented in adult equivalencies, functional influences of SDN from hatchery smolt mortality are likely to differ. Salmon‐derived nutrients from hatcheries enter food webs through largely piscivorous pathways whereas SDN from adult carcasses enter food webs through multiple pathways at multiple trophic levels. The SDN from hatchery‐origin smolts probably influence different components of the food web more than do adult carcasses and have the potential to more directly affect predator populations.

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Section: Methodsmentioning

confidence: 99%