Graduation Date

Summer 2022

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Fisheries

Committee Chair Name

Mark Henderson

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Wes Larson

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Andre Buchheister

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Jose Marin-Jarrin

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Fisheries

Abstract

Juvenile Chinook Salmon (Oncorhynchus tshawytscha) migrating through the Sacramento – San Joaquin Delta (the Delta) in central California have higher mortality rates than salmonids migrating through other west coast estuaries. Some hypotheses for high mortality rates include entrainment into water export facilities, physical alterations of the river system, and predation. Of these factors, predation is considered the least understood but may have the largest impact. Predation from large populations of non-native piscivorous fishes in the Delta is believed to effect abundances of Central Valley Chinook salmon, however sufficient data supporting this hypothesis is scarce. In this study, I investigate the possibility of using three molecular methods (qPCR, metabarcoding, SNP) to improve fish diet analyses by measuring the gastric evacuation of Chinook salmon in the stomachs of two common Delta predators, largemouth bass (Micropterus salmoides) and channel catfish (Ictalurus punctatus). Before molecular analysis can occur using field samples, it is important to conduct laboratory feed trials to determine how factors affect gastric evacuation and the detectability of DNA within predator digestion systems. My experiment was conducted to determine gastric evacuation of Chinook DNA and visual decay of organic tissue within the digestive tracts of two common piscivores in the Delta at different temperatures (15.5˚C and 18.5˚C) and feed ratios (predator weight: prey weight). Results from metabarcoding and qPCR analysis indicate greater detection ability and longer durations of digestion at higher feed ratios and decreased temperature. Temperature and ratio effect was species dependent with a larger effect on evacuation within channel catfish compared to largemouth bass. Channel catfish also had slower digestion rates, indicating lower metabolism and a longer duration of DNA detection. Lastly, visual degradation of prey tissue followed a highly correlated decay pattern to metabarcoding read count and qPCR copy number over time. Gastric evacuation results from this study can provide information for future models on the effect of species, time, temperature, and feed ratio on digestion rate needed to predict population level predation occurring on native salmonids.

Citation Style

APA

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