Jacob Dingwall

Topic

Environmental and Anthropogenic Factors Limiting Abandoned Spawning Site Reoccupation by Pacific Herring (Clupea pallasii) in the Strait of Georgia

Department of Biology

Date & location

• Wednesday, June 24, 2026
• 10:00 A.M.
• Clearihue Building, Room B007

Examining Committee

Supervisory Committee

• Dr. Amanda Bates, Department of Biology, University of Victoria (Supervisor)
• Dr. Benjamin Neal, Department of Biology, UVic (Member)
• Dr. Peter Ross, Healthy Waters Program, Raincoast Conservation Foundation (Outside Member)

External Examiner

• Dr. John Driscoll, Marine Conservation Manager, David Suzuki Foundation

Chair of Oral Examination

• Dr. Quentin Mackie, Department of Anthropology, UVic

Abstract

Small pelagic fish sustain some of the world's most productive marine fisheries and occupy central roles in coastal food webs, yet many populations remain vulnerable to range contractions that persist well beyond periods of biomass recovery. Pacific herring (Clupea pallasii) exemplify this pattern in the Strait of Georgia (SOG), British Columbia, where spawning has compressed geographically over recent decades and degraded habitat quality at abandoned grounds has been proposed as a barrier to reoccupation. We evaluated two axes of habitat quality: spawning vegetation availability and contaminant risks.

For vegetation, 36 years of SCUBA-based egg deposition surveys informed a generalized additive mixed model (GAMM) predicting egg-laying patterns across vegetation types. Sargassum muticum, an invasive brown macroalga, was the most heavily used substrate across the SOG. Inter- and subtidal vegetation was mapped at six abandoned and two occupied spawning sites by remotely operated vehicle (ROV) in spring 2024; ROV-derived data were applied to the GAMM to estimate egg-laying capacity at each site. Vegetation availability did not limit reoccupation, and a selection ratio analysis confirmed strong herring preference for S. muticum over other substrate types.

For contaminants, marine water and surface sediment samples were collected across eight sites in spring and fall 2024. Sediment was screened for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), per- and polyfluoroalkyl substances (PFAS), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), alkylphenols, bisphenols, and pharmaceuticals and personal care products (PPCPs); water was additionally analyzed for 39 metals. Sediment PAH concentrations were highly heterogeneous, ranging from 1 ng/g at Qualicum Bay to 56,842 ng/g at Transfer Beach, where a legacy coal-washing operation contributed to Probable Effect Level exceedances for 11 PAH analytes. PBDE concentrations exceeded interim sediment quality guidelines at six of eight sites. PAH concentrations in water were low and more spatially uniform (spring median: 7.9 ng/L; range: 2.7-59 ng/L).

We characterised biological risk for the dominant contaminant of concern using a PRISMA-guided synthesis of 40 effective concentration 10% (EC10) endpoints from six herring embryotoxicity studies. Derived EC10 values spanned two orders of magnitude (0.12-13.2 μg/L ΣPAH); a Clupea intraspecies sensitivity distribution yielded an HC5 of 0.18 μg/L and HC10 of 0.24 μg/L. Spring median dissolved PAH concentrations fell approximately 23-fold below the HC5, indicating limited acute embryotoxic risk at most sites. Although overall contaminant concentrations do not suggest immediate concern, fewer than 10% of measured contaminants have established environmental quality guidelines, leaving contaminant-embryo risk thresholds largely uncharacterized. Overall results suggest that habitat degradation and localised contaminant burdens may be affecting herring reoccupation. Further research is warranted to clarify SOG-wide changes in spawning ground usage.