Food web ecology of Lahontan Cutthroat Trout and trophic dynamics of selenium in Omak Lake, Washington
The adaptation of Lahontan cutthroat trout (LCT) - Oncorhynchus clarkii henshawi to Omak Lake’s water (the largest alkaline lake in Washington state) is a great example of fish survival and evolution in harsh environments. LCT is the only game fish in Omak Lake and became the apex predator. The rese...
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| Other Authors: | , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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Washington State University
2022
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| Online Access: | https://doi.org/10.7273/000004988 https://rex.libraries.wsu.edu/esploro/outputs/doctoral/Food-web-ecology-of-Lahontan-Cutthroat/99901019237201842 https://rex.libraries.wsu.edu/view/delivery/01ALLIANCE_WSU/12397237160001842/13397237150001842 |
| Summary: | The adaptation of Lahontan cutthroat trout (LCT) - Oncorhynchus clarkii henshawi to Omak Lake’s water (the largest alkaline lake in Washington state) is a great example of fish survival and evolution in harsh environments. LCT is the only game fish in Omak Lake and became the apex predator. The research aimed to understand (i) how LCT thrived in alkaline waters with potentially low prey availability, (ii) what are the main prey items feeding LCT? (iii) what dietary limitations could threaten LCT sustainability and growth? Additionally, alkalinity combined with oxidizing conditions promotes the speciation of potentially toxic selenium (Se) ions (selenate and selenite). Thus, another research question was (iv) how Se could be biomagnifying in Omak’s food web. Therefore, I performed a stomach content analysis (SCA) to assess LCT's prey consumption. Then, stable isotopes (δ15N and δ13C) analysis (SIA) validated SCA and refined LCT’s diet via a mixing model. Furthermore, otolith reading provided LCT’s age estimation. Se was assayed via ICP-MS, and biomagnification was estimated via the trophic magnification factor (TMF) model. The SCA results from 2018 – 2021 identified the 10 largest prey biomasses proving an abundance of prey despite the alkaline conditions: Peamouth, Coleoptera, cannibalized-LCT, Longnose sucker, Odonata, Redside shiner, Diptera, Hymenoptera, Sculpin, and gastropods. The SIA mixing model predicted the piscivore feeding transition started on LCT (1–3 years) but also recognized the significance of invertebrate prey (aquatic and terrestrials) for all LCT sizes. Thus, a combination of invertebrates and prey fish were the main items feeding LCT. The ontogenetic shift to a piscivore feeding was detected in large LCT, 4-6 years. Dipterans were found in all LCT sizes confirming generalist feeding, but the abundance of prey fish might be a significant limiting factor regulating LCT’s growth. The Se concentrations were below the 4-ppm toxicity threshold for all fish and invertebrates analyzed. Nevertheless, ... |
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