M.S. Thesis Defense: Drew Porter

Friday, July 29, 2022 @9:00 a.m.
BP Design Theater, Room 401, Engineering Learning and Innovation Facility, UAF

Drew Porter (WERC/CFOS | M.S. Marine Biology Candidate)

Acute toxicity of copper to three species of Pacific salmon fry in water with low hardness and low dissolved organic carbon

Abstract: Proposed development of a large copper-gold-molybdenum mine (Pebble mine) within Alaska’s Bristol Bay watershed has raised concerns over potential impacts to the culturally, ecologically, and economically important Pacific salmon species present in waterbodies near the mineral deposit. Copper (Cu) is acutely toxic to fish and the primary model used for predicting copper toxicity to aquatic organisms, the biotic ligand model, is inaccurate under the low hardness and dissolved organic carbon water quality conditions typical of the region. Accordingly, here acute copper exposure bioassays using water with relevant chemistry (~13 mg/L hardness and 0.8 - 1.8 mg/L DOC) and sockeye (Oncorhynchus nerka), Chinook (O. tshawytscha), and coho salmon (O. kisutch) fry were performed to determine lethal concentrations of copper and to assess the accuracy of model estimates. The acute median lethal concentrations for sockeye, Chinook, and coho salmon were 34.2 (95% confidence interval [CI]: 33.2, 36.2), 23.9 (95% CI: 20.3, 27.4), and 6.3 µg Cu/L (95% CI: 5.6, 7.0), respectively. The biotic ligand model estimated median lethal concentration for sockeye salmon was less than the experimental value by a factor of 0.97. Model estimates for Chinook and coho salmon were greater than experimental values by factors of 1.49 and 2.40, respectively. Median lethal copper accumulation values for the three study species were also estimated to assess their relative sensitivities to copper. The median lethal copper accumulation values for sockeye, Chinook, and coho salmon were 3.9 (95% CI: 3.5, 4.4), 1.7 (95% CI: 1.3, 2.2), and 0.9 nmol Cu/g wet weight (95% CI: 0.7, 1.0), respectively. These results indicate that copper sensitivities were lowest for sockeye, intermediate for Chinook, and highest for coho salmon fry. These findings are concerning given the propensity of coho salmon to spend greater lengths of time rearing in waterbodies near the mineral deposit than Chinook or sockeye salmon. This study has demonstrated the need for in depth considerations of copper contamination impacts at the species level. These findings can be used to calibrate the biotic ligand model, increasing the accuracy of predictions for sockeye, Chinook, and coho salmon.

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