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Faculty of Graduate Studies

Jessica Qualley

  • B.Sc. (University of Victoria, 2016)
Notice of the Final Oral Examination for the Degree of Master of Science

Topic

Otolith stable isotopes infer partial migration in adult Pacific Herring (Clupea pallasii) in the Strait of Georgia

Department of Biology

Date & location

  • Friday, September 4, 2026
  • 10:00 A.M.
  • Clearihue Building, Room B007

Examining Committee

Supervisory Committee

  • Dr. Francis Juanes, Department of Biology, University of Victoria (Supervisor)
  • Dr. John Dower, Department of Biology, UVic (Member)
  • Dr. Jennifer Boldt, Research Scientist, Fisheries and Oceans Canada (Outside Member)

External Examiner

  • Dr. Brian Hunt, Institute for the Oceans and Fisheries, University of British Columbia

Chair of Oral Examination

  • Dr. Iain McKechnie, Department of Anthropology, UVic

Abstract

The Strait of Georgia Pacific herring (Clupea pallasii) population is currently managed as a migratory stock that moves between spring spawning grounds in the Strait of Georgia (SOG) and summer feeding grounds off the continental shelf of West Coast Vancouver Island (WCVI). However, a proportion of the adult population remains in the Strait of Georgia through summer as non-migratory herring. Previous estimates of summer non-migratory herring have not been quantified, and their prevalence represents a knowledge gap in our understanding of sub-stock structure as it relates to B.C. herring fisheries management. Whole otolith stable isotopes of δ13C and δ18O were used to investigate migration life history diversity in the SOG population. Otoliths from summer SOG, summer WCVI, and spring SOG spawners were sampled between 2020-2022 to develop a logistic regression model of whole otolith δ13C and δ18O. The model was applied to spring SOG spawners to investigate differences in early growth and adult traits associated with migration type. Otolith-based classifications estimated 30-33% of SOG spring spawners sampled from the DFO Roe Herring Test Fishery were classified as non-migratory (SOG inshore) herring, yet a high frequency of spawners occupied the intermediate isotopic space between summer SOG and WCV baseline groups, suggesting intermediate environmental histories. Spawning fish may exhibit a continuum of environmental histories rather than discrete migratory and non-migratory types. No relationship was found between first-year growth (proxied by otolith increment distance) and migration strategy detected from otolith stable isotopes, suggesting that other mechanisms influence migration decisions at some other life stage. Differences in adult size and condition; however, were detected as migratory herring were heavier, longer, and had lower condition compared to non-migratory herring. A negative association between growth and condition may reflect a potential trade-off in which long-distance migrants benefit from structural growth in size and weight gains from offshore feeding but arrive at spawning grounds in poorer condition due to the high energetic costs of a return migration, relative to stationary non-migratory herring. This study indicates greater migration life-history diversity than previously assumed under the current single, migratory stock structure. The otolith stable isotope tag developed in this study can potentially quantify uncertainties in SOG stock structure as it relates to migration life-history diversity, the impacts of fisheries on alternative migration strategies, and the underlying drivers that maintain migration life-history diversity in the SOG herring population.

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