Graduation Date

Summer 2019

Document Type

Thesis

Program

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

Committee Chair Name

Darren Ward

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Daniel Barton

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Mark Henderson

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Fisheries

Abstract

Juvenile Coho Salmon (Oncorhynchus kisutch) in coastal California streams exhibit various life history strategies during their freshwater development. One strategy of interest to managers and conservationists is the early migrant. Juvenile early migrants emigrate from natal habitat into lower parts of the watershed or estuary during their first fall or winter, where they rear before migration to the ocean. By contrast, the more prevalent spring migrant resides in natal reaches over the winter and migrates directly to the ocean the following spring. Salmon monitoring programs generally estimate juvenile production and demographic rates using only spring migrants, and these estimates are likely biased without the inclusion of early migrants. In Freshwater Creek in Northern California, an ongoing monitoring program PIT-tags juvenile Coho Salmon in the fall and winter, detects their movements throughout the stream and estuary over their first winter, captures spring out-migrants, and then detects adults as they return to spawn. Using six years of this mark-recapture data (2013-2018), I constructed a full life cycle multistate model to estimate (1) over winter survival of both the spring and early migrating juveniles, (2) apparent marine survival of spring and early migrating juveniles, (3) the probability of fall tagged juveniles migrating early and, (4) the probability of each juvenile life history returning as jacks. Overwinter survival for all three cohorts and all life histories ranged from 25-73%. In cohort one, overwinter survival for spring migrants was greater than the early migrants: overwinter survival was between 38-53% for spring migrants (depending on analysis assumptions) compared to 26% for early migrants; overwinter survival for the two life histories was indistinguishable in the other two cohorts. Apparent marine survival, including all cohorts and life histories ranged from 1.6-4.9%. Marine survival was indistinguishable between juvenile life history strategies likely due to small sample sizes. A power analysis performed with simulated data, to estimate the sample size of fall tags necessary in order to distinguish between juvenile life histories; this ranged from 3500-6000 tags. The transition probability to the jack state ranged from 1.5-55.8% and was indistinguishable between life history strategies.

Multistate models provide the opportunity to incorporate life history diversity into estimates of population demographic rates. Use of these models and ongoing monitoring effort will continue to add new insights into Coho Salmon life history variation and the consequences for populations.

Citation Style

Transactions of the American Fisheries Society

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