Graduation Date

Summer 2019

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

Darren Ward

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Nicholas Som

Third Committee Member Affiliation

Community Member or Outside Professional

Fourth Committee Member Name

Daniel Barton

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Fisheries

Abstract

Accounting for life history diversity and overwinter survival of juvenile Coho Salmon is important to inform restoration and recovery efforts for this threatened species. Multiple seaward migration patterns of Coho Salmon have been identified, including spring fry migrants, fall and winter parr migrants, and spring smolt migrants. Previous studies have indicated that spring smolt migrants have low overwinter survival rates while they are rearing in upstream habitats, suggesting that freshwater overwinter survival may be one factor that limits smolt production. However, previous research did not account for the early emigration of fall and winter parr migrants from the study area, which most likely negatively biased their overwinter survival estimates. Furthermore, previous mark-recapture methods aggregated continuous detection data into course seasonal scales in order to estimate movement and survival. In an effort to refine previous methodology, I developed a multi-state model that allowed for estimation of early emigration and survival rates in space and time by having weekly time-varying occasions paired with discrete spatial states. I conducted extensive simulation trials to validate my use of the multi-state model on an existing 4-year PIT tag dataset in Freshwater Creek, California. Overwinter survival for spring smolt migrants was estimated as a function of average length at time of fall tagging for each year, and ranged from 0.87 to 0.90. Conditional on survival, early emigration estimates ranged from 0.34-0.40 annually. Results from the top model suggested that fish size during initial capture in the fall had a positive effect on overwinter survival of spring smolt migrants, and a negative effect on early emigration rates of fall and winter parr migrants. Additionally, streamflow had a positive effect on early emigration rates of fall and winter parr migrants. These results provide evidence that substantial numbers of smaller juveniles are emigrating early from upstream rearing habitat. This implies that previous estimates of low overwinter survival of Coho salmon could be due to high emigration rates to alternative rearing locations. Given the apparent diversity within the juvenile portion of the life cycle of Coho Salmon, multiple emigration patterns should be considered in the design of future research, monitoring, and restoration projects.

Citation Style

Transactions of the American Fisheries Society

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