Graduation Date

Winter 2024

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources: option Environmental Science and Management

Committee Chair Name

Dr. Alison O’Dowd

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Darren Ward

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Mark Henderson

Third Committee Member Affiliation

Community Member or Outside Professional

Fourth Committee Member Name

Seth Ricker

Fourth Committee Member Affiliation

Community Member or Outside Professional

Keywords

Northern California, Humboldt Bay, Coho Salmon, restoration, off-channel restoration, ponds, salmon diet, invertebrate community, prey availability, survival, movement, salmon growth

Subject Categories

Fisheries

Abstract

Anthropogenic degradation of off-channel floodplain habitats has contributed to widespread declines in Pacific salmonid populations. These habitats are critical to the survival and growth of juvenile Coho Salmon during their first year of life. Restoring connectivity between mainstem and floodplain habitats could provide juvenile salmonids access to a mosaic of heterogenous foraging opportunities, with important consequences for salmonid growth and survival. I analyzed the diet, growth, and survival of juvenile Coho Salmon rearing in three restored off-channel ponds and adjacent mainstem habitats in Humboldt Bay tributaries to evaluate project performance. Juvenile Coho Salmon diet composition was significantly different among sites and habitats except for the two estuarine habitats. Some invertebrate prey taxa (i.e., Coenagrionidae, Isopoda, Dytiscidae, Mysidae, and winged adults) comprised large proportions of juvenile Coho Salmon diets in off-channel ponds, but were much less common or altogether absent in diets at other sites or habitats. Significantly higher growth of juvenile Coho Salmon was observed in a restored off-channel pond in estuarine habitat relative to the adjacent mainstem, but growth in constructed off-channel ponds was similar to growth in the adjacent main stem for freshwater ponds. Higher invertebrate biomass in juvenile Coho Salmon diets did not coincide with higher fish growth. Transition probabilities between mainstem and off-channel habitats indicated that juvenile Coho Salmon may have not been able to consistently move between these habitats at two out of three study sites. Differences in prey resource portfolios, fish passage, and density-dependent effects are likely drivers of variation in growth across sites and habitats, but inference on survival is limited at the project scale. These results can help inform future biological monitoring strategies for off-channel restoration projects.

Citation Style

APA

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