Thesis
IMPACT OF ANTICOAGULANT RODENTICIDES ON JUVENILE COHO SALMON (ONCORHYNCHUS KISUTCH): ASSESSING LETHAL & SUBLETHAL EFFECTS
Washington State University
Master of Science (MS), Washington State University
05/2025
DOI:
https://doi.org/10.7273/000007446
Abstract
Whole island rodent eradications in the Aleutian Islands rely on aerial baiting with anticoagulant rodenticides (ARs) to protect native seabirds. While aerial applications aim for precision, pellets inevitably enter aquatic environments, raising concerns about non-target impacts on salmonids. However, toxicity data for aquatic species are limited. To address this gap, we used coho salmon (Oncorhynchus kisutch) to generate dose-response curves via intraperitoneal (IP) injections in corn oil, estimating 96-hour LD50 values of 80.1 µg/g (95% CI: 65.8–94.4 µg/g) for brodifacoum and 60.7 µg/g (95% CI: 55.9–65.5 µg/g) for diphacinone. IP injections deliver chemicals in oil for rapid uptake, but acetone is sometimes needed in the oil to maintain higher concentrations of ARs in solution. We found that the presence of acetone in injection stock significantly reduced the toxicity of diphacinone but not brodifacoum. The acetone may impact diphacinone bioavailability or metabolism, whereas brodifacoum is known to be poorly metabolized prior to elimination. Tissue analysis supported a difference in metabolism. In moribund fish dosed with 85 µg/g of brodifacoum, liver and muscle concentrations averaged (SD) 105.6 (31.4) µg/g and 21.5 (3.4) µg/g, respectively, with no significant reduction in surviving fish sampled at 96 hours. In contrast, diphacinone concentrations in moribund fish (100 µg/g dose) started at 176.5 (73.6) µg/g in the liver and 22.7 (5.1) µg/g in the muscle but were 0.899 (0.299) µg/g and 0.063 (0.053) µg/g, respectively, in survivors at 96 hours. Clotting time was used as a sublethal endpoint and was measured over time after administering a single sublethal dose. When exposed to 55.0 µg/g (LD14) of brodifacoum, coho had significantly longer clotting times at 72 and 96 hours post-injection. Clotting times returned to baseline by 120 hours post-injection. We did not observe significantly increased clotting times within 144 hours after dosing coho with 50 µg/g (LD2) of diphacinone. This suggests that diphacinone may affect coho through a different mode of action.
Metrics
5 File views/ downloads
8 Record Views
Details
- Title
- IMPACT OF ANTICOAGULANT RODENTICIDES ON JUVENILE COHO SALMON (ONCORHYNCHUS KISUTCH)
- Creators
- Lillian Pavord
- Contributors
- Jenifer McIntyre (Chair)John Stark (Committee Member)Allan Felsot (Committee Member)Aaron Shiels (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of the Environment (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 65
- Identifiers
- 99901220323801842
- Language
- English
- Resource Type
- Thesis