Satellite Remote Sensing of Herring (Clupea pallasii) Spawning Events: A Case Study in the Strait of Georgia

In this proof‐of‐concept study, we show how satellite remote sensing can be used to detect and monitor Pacific herring spawning events in the Strait of Georgia (SoG), British Columbia, Canada. Multi‐sensor medium‐resolution (∼300 m) and high‐resolution (3–30 m) images reveal bright waters in the SoG due to high concentrations of herring milt from multiple spawning events. The milt‐infused waters lead to enhanced reflectance with unique spectral characteristic that can be distinguished from other optically active constituents such as suspended sediments, coccolithophores, “whiting” particles, and shallow bottoms. While the medium‐resolution images may be used to search for cloud‐free and potential spawning sites, high‐resolution images show more details in milt distributions. Given the increased availability of high‐resolution satellite imagery at the global scale, this demonstration may promote more applications of satellite remote sensing in fisheries and ocean ecology research. Plain Language Summary This proof‐of‐concept study demonstrates that certain fish spawning events can produce a bright enough signal in satellite images that may allow satellite‐based observations to assist with some aspects of fisheries management. Specifically, herring spawning events in the Strait of Georgia (British Columbia, Canada, and the Gulf of Alaska) can be observed in images collected by various satellite sensors, and the spatial extent of some spawning events can also be characterized and quantified. This is because the reflectance shape of waters rich in herring milt is unique and allows herring spawn to be distinguished without ambiguity relative to other waters. The ability to detect these spawning events has major implications for satellite remote sensing, which can provide complementary information to data collected from expensive and weather‐dependent in situ SCUBA and shipboard surveys. Further, satellite observations could be used to test the completeness and geographical precision and accuracy of other surveys, especially airborne surveys, for example through characterizing herring spawning events at synoptic scales. Key Points Satellite remote sensing is shown to be able to detect herring spawning events in certain regions Coastal waters rich in herring milt show unique reflectance shapes that can be distinguished from other bright features Multi‐sensor images reveal spatial and temporal characteristics of herring spawning events in the Strait of Georgia