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February 12, 2025

Every spring, the coastal waters of Vancouver Island turn a striking turquoise as Pacific herring gather to spawn. This breathtaking natural phenomenon, crucial to B.C.’s marine ecosystem, has traditionally been monitored by Fisheries and Oceans Canada (DFO) using aerial surveys and on-site observations. Now, UVic researchers are pioneering a new approach—tracking herring spawning from space.

Loic Dallaire, a master’s student in the Spectral Remote Sensing Lab within UVic’s Department of Geography, is working to develop a satellite-based monitoring system. His research, in collaboration with the Pacific Salmon Foundation, aims to enhance existing tracking methods by providing a broader and more consistent view of spawning events along B.C.’s coast.

Why Use Satellites?

DFO’s traditional approach relies on visual surveys from planes and boats to document where herring are spawning. However, these methods have spatial and temporal limitations, as they can only cover certain areas at specific times. By using satellite imagery, the UVic research team can:

- Expand monitoring beyond core fishing areas
- Track year-to-year changes in spawning locations
- Assess environmental factors affecting herring populations

"The method we’re developing is absolutely new," says Dallaire. "Using satellite we can expand both spatially and temporally. So that’s the goal, to look outside of the core fishing area."

What Causes the Turquoise Water?

The vibrant blue-green color associated with herring spawning is caused by milky reproductive fluids released by male herring. While the satellite imagery cannot directly count fish or eggs, it can detect the extent and frequency of male spawning events, helping researchers estimate herring activity across large regions.

Why This Research Matters

Pacific herring are a keystone species in B.C.’s marine ecosystem. Their populations impact salmon, whales, seabirds, and other marine life. By improving tracking methods, this research can provide valuable data for conservation efforts, helping to assess how factors like pollution and temperature changes affect herring populations.

Last year, herring returned in strong numbers around Tofino following several years of fishing closures. This year’s spawning season is just beginning, with activity expected to peak in March.

Dallaire and his team will be sharing satellite data updates in the Pacific Herring Spawn Reporting – IMAWG Facebook group, where the public can stay informed about this year’s herring run.