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Grantee Research Project Results

Grantee Research Project Results

Gillnet Injury and Mercury Loading in Salmon Consequences of Fishery-Related Delayed Mortality on Sockeye Salmon Stocks and the Threat of Mercury Import to Freshwater Systems by Anadromous Salmon

EPA Grant Number: F07E10237
Title: Gillnet Injury and Mercury Loading in Salmon Consequences of Fishery-Related Delayed Mortality on Sockeye Salmon Stocks and the Threat of Mercury Import to Freshwater Systems by Anadromous Salmon
Investigators: Baker, Matthew
Institution: University of Washington - Seattle
EPA Project Officer: Boddie, Georgette
Project Period: September 1, 2007 through September 1, 2010
RFA: STAR Graduate Fellowships (2007)
Research Category: Academic Fellowships , Aquatic Ecology and Ecosystems , Fellowship - Aquatic Systems Ecology



This research focuses on two important pollution concerns related to salmon (Oncorhynchus spp.) in the North Pacific. The first examines the incidence of pre-spawning mortality among salmon that return to natal streams damaged by their interaction with fishing gear. The second component of the project investigates mercury contamination in salmon and the role of salmon in transferring methyl mercury from marine to freshwater environments. Specifically, this project will:

  • Determine the incidence and severity of fishery-related damage to sockeye salmon stocks that return to natal streams and determine its effect on pre-spawning mortality
  • Model the loss of spawners resulting from unaccounted, non-yield, fishery-related mortality and quantify its relevance with regard to recruitment and the designation of optimal escapement targets
  • Determine how discounting lost spawners alters cost-benefit analyses of escapement targets and develop a decision-making framework to evaluate trade-offs between management objectives
  • Quantify methyl mercury contamination in salmon spawning in Bristol Bay, AK tributaries
  • Determine the threat of mercury contamination to resident fish resulting from salmon subsidies to freshwater ecosystems


This research explores the consequences of fishery-related damage to escaped stocks by distinguishing between total escapement (absolute number of salmon that escape the fishery) and effective escapement (number of escaped salmon that remain capable of reproduction). Directed field sampling of the incidence of injury, mark-recapture studies of mortality rates, and long term data sets of spawner-recruit abundances will be synthesized to explore this distinction and will be incorporated into harvest optimization models using Bayesian decision analysis. Mercury contamination will be measured through the extraction of tissue samples in spawning salmon. Total mercury in the tissue will be determined by cold vapor atomic absorption spectrophotometry. Methyl-mercury analysis will be conducted by alkaline-alcohol digestion of the samples followed by gas chromatography.

Expected Results:

Research on pre-spawning mortality will (1) identify and assign probabilities to uncertainties of sockeye salmon spawner-recruit dynamics; (2) distinguish between total and effective escapement and integrate this distinction into stock-recruitment models; and (3) employ a decision analysis framework to evaluate management options. Such analyses will address explicit concerns related to the Bristol Bay, Alaska fishery. Analysis of mercury contamination will provide a crucial baseline of methyl-mercury contamination in salmon and better inform estimates of bioaccumulation of heavy metal contaminants in populations of resident fish targeted by recreational fishers throughout the North Pacific.

Supplemental Keywords:

salmon; mercury contamination; aquatic food webs; marine-derived nutrients; incidental mortality; stock-recruitment dynamics, fisheries management; density dependence; economic discounting,

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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