Graduation Date
Fall 2017
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
Eric Bjorkstedt
Second Committee Member Affiliation
HSU Faculty or Staff
Third Committee Member Name
Chris Dugaw
Third Committee Member Affiliation
HSU Faculty or Staff
Subject Categories
Fisheries
Abstract
Historic land use practices and associated habitat degradation have led to significant declines in coho salmon (Oncorhynchus kisutch ) populations across their range. In California they are a state and federally listed species, requiring population monitoring and management plans tailored towards recovery. Traditionally, juvenile coho salmon in California were thought to spend approximately one year in their natal freshwater habitats before migrating to sea the following spring and summer as smolts. However, recent work has documented considerable variation in juvenile life history and migration timing. Specifically, juveniles that migrate downstream prior to one year of age and spend their winter rearing in estuary habitat have been shown to produce significant adult returns. Using 14 years of life-stage-specific survival and movement data collected on Freshwater Creek in northern California, I constructed a habitat-base life cycle model to evaluate expected population response to restoration actions, and to incorporate life history diversity into population projections. This modeling effort is divided into three sections: (1) parameterize stage specific survival rates and probability of expressing an early emigrant life history; (2) conduct sensitivity analysis to quantify which life stages are most influential in determining population status; (3) use stochastic simulations to quantitatively evaluate how population dynamics and extinction risk are affected by inclusion of life history diversity and alternative restoration scenarios. The resulting analyses showed that, across locations and years, between 3-29% of juvenile coho are early migrants to the stream estuary ecotone during their first winter. The majority of early migrants originated in the main-stem reaches lower in the watershed. Subsequent sensitivity analysis identified marine survival and smolt emigrant overwinter survival as highly influential in the long-term trends for this population. While the proportion of individuals expressing an ‘early emigrant’ life history variant is significant, this strategy showed low sensitivity relative to other life stages in defining long-term population growth under this modeling construct. In contrast, 50-year population simulations showed significant gains in adult escapement up to 43% when early emigrant life histories were included. This suggests that while alternative life history variants may not be the single greatest driver of population growth, their exclusion in management models may constitute a significant oversight in population management. Additionally, the probability of local population extinction was reduced substantially from 36% to 8% with the incorporation of life history diversity in the modeling structure. Historic coho salmon rearing habitats have been vastly diminished during the last 100 years in both stream and estuary areas. This modeling approach can help to identify sites to focus habitat restoration where it can strengthen individual populations’ long-term growth or abilities to persist in the face of environmental stochasticity.
Citation Style
APA
Recommended Citation
Scheer, Gabriel, "A population model for Coho salmon (Onchorhynchus kisutch) in freshwater creek: evaluating the effects of life history variation and habitat restoration" (2017). Cal Poly Humboldt theses and projects. 105.
https://digitalcommons.humboldt.edu/etd/105