Graduation Date
Summer 2026
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Fisheries
Committee Chair Name
Darren Ward
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Jose Marin Jarrin
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Nicholas Som
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Eric Bjorkstedt
Fourth Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fifth Committee Member Affiliation
Community Member or Outside Professional
Keywords
Chinook salmon life history diversity, Bar built estuary, Mattole River, Northern California, Lagoon, Otolith microchemistry, Outmigration timing
Subject Categories
Fisheries
Abstract
Bar-built estuaries are rivermouth confluences characterized by periods of disconnection between the river and the ocean due to a sandbar that builds across the mouth. Sandbar timing characteristics vary between years and between systems, but when closed, a lake-like lagoon forms in the estuary footprint. The Mattole River has a bar-built estuary that forms in late spring or early summer, often overlapping with juvenile Chinook salmon outmigration. Juveniles that do not leave the river before the bar closes must remain in the lagoon until the mouth opens in fall. The purpose of this thesis was to understand if lagoon-rearing is a successful life history strategy that contributes adults to the spawning population in the Mattole River. To accomplish this, I 1) used adult Chinook salmon otolith microchemistry to determine juvenile life history pathways of successful spawners, 2) used historical downstream migrant trap data to predict outmigration timing for 31 years and compared that to the timing of bar closure, and 3) conducted field sampling to quantify juvenile Chinook abundance in the lagoon during periods of mouth closure in 2024 and 2025. Evidence shows that lagoon rearing is not a dominant life history in the Mattole River, but lagoon closure does constrain the length of freshwater residence. In most years, the mouth closes after the majority of fish have migrated downstream but in dry years with early mouth closure, a higher proportion of juvenile Chinook remains in the lagoon. Elevated juvenile mortality is apparent among lagoon-reared fish, but cohort level impacts seem minimal or year-specific.
Recommended Citation
Held, Emma, "Contribution of lagoon-rearing juvenile Chinook salmon (Oncorhynchus tshawytscha) to the adult spawning population in the Mattole River" (2026). Cal Poly Humboldt theses and projects. 2602.
https://digitalcommons.humboldt.edu/etd/2602