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

HSU Faculty or Staff

Subject Categories

Fisheries

Abstract

Estuaries are commonly touted as nurseries for out-migrating salmonids, providing higher prey availability than streams, a physiological transition zone, and refugee from marine predators. Yet the diversity of estuaries makes it difficult to generalize the effect they have on salmonid recruitment. In bar-built estuaries, sandbars form at the mouth of rivers during periods of low flow, closing access to the ocean and disrupting outmigration. In this thesis, I evaluated how residency in a bar-built estuary affects the growth, survival, and ultimately recruitment of Chinook salmon (Oncorhynchus tshawytscha) in Redwood Creek, California. I conducted a mark-recapture experiment on out-migrating juveniles during the summer of 2018 to determine estuary abundance, growth, and survival. I used scales and sagittal otoliths collected from spawning adult carcasses to quantify the contribution of different juvenile life histories to the adult population. I then integrated these data and monitoring data collected from spawning ground surveys, rotary screw traps, and estuary seines to create a stage-structured matrix model.

Juveniles that remained in the estuary after the mouth closed were larger at ocean entry than ocean rearing juveniles that entered the ocean earlier in the spring. However, estuary-rearing juveniles grew less and ultimately were smaller than ocean rearing juveniles were prior to winter. Despite having a larger ocean entry size, estuary rearing juveniles had lower survival from river outmigration to adult return than ocean rearing juveniles and contributed disproportionately less to the spawning population. Lack of marine influence and low river flow are common attributes of bar-built estuaries that may lower food availability and deteriorate conditions in these estuaries. Levees constructed in lower Redwood Creek prevent flooding and establishment of marsh and floodplain habitat, potentially majorly limiting the productivity of the estuary and salmonid growth. Restoration efforts designed to address limitations to growth in the estuary such as low food availability and high temperatures are needed to increase the ocean survival and ultimately contribution of estuary juveniles to the population.

Citation Style

Transactions of the American Fisheries Society

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