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UBC Theses and Dissertations

Vulnerability assessment for juvenile sockeye salmon using biological indicators Andersen, Alicia M. M.


Pacific sockeye salmon populations have been declining since the 1980s. Various life stages have been identified to impact these declines, but the early marine phase is particularly important. Juvenile salmon growth and condition during this phase is critical to their success in evading predators and surviving their first marine winter. Therefore, environmental factors that limit foraging success have been identified as potential causes for salmon declines, such as ocean temperature, prey quantity and quality. The purpose of this study was to 1) determine if temperature and zooplankton biomass explain seasonal and annual variation of salmon growth and condition metrics (RNA:DNA, essential fatty acids (EFAs), Fulton’s K) and 2) develop a Climate Change Vulnerability Assessment (CCVA) framework for salmon during their early marine phase incorporating environmental factors identified through expert judgement and biological indicators. Juvenile sockeye salmon were collected from the Discovery Islands, British Columbia from 2015-2020 during their marine outmigration from May-July, and temperature and zooplankton biomass were collected from the central and northern Strait of Georgia from April-July, along the outmigration route. A distinct seasonal pattern emerged of salmon with better condition (higher K and EFAs) migrating at the end of the season, and salmon with poorer condition migrating at the beginning. Analyses determined that temperature was positively associated with RNA:DNA (GLM, p < 0.05), but negatively associated with EFAs and K (GLM, p < 0.05). Zooplankton biomass was also associated with RNA:DNA, EFAs, and K (GLM, p < 0.05), but the directionality depended on the zooplankton group. I also developed a CCVA framework for juvenile salmon incorporating environmental factors elicited from experts. These environmental factors included temperature, prey availability (biomass, quality, size, phenological match / mismatch), predators, and parasites / disease (e.g., sea lice). The biological indicators identified by the previous models included condition metrics RNA:DNA, EFAs, and length-weight residuals. I applied this framework to Fraser River sockeye salmon from 2015-2020. The CCVA predicted that all six years had relatively low vulnerability. This thesis provides insight into factors impacting salmon and develops a novel approach to determine salmon vulnerability which could be used to predict future salmon returns.

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