Satellite Spots a Spawn

Spawning season has arrived for Pacific herring (Clupea pallasii) in the waters off British Columbia, Canada. Every year from mid-February to early May, thousands of these small, silvery fish gather in shallow coastal areas around Vancouver Island, creating a spectacle that can even be seen by satellites.

The sheltered waters in Barkley Sound, on the southwestern side of Vancouver Island, are common sites for these spawning events. On February 19, 2026, the Landsat 9 satellite captured early-season activity near Forbes Island. During these events, female herring lay eggs that adhere to various surfaces like kelp, seagrass, and rocks. Male herring release milt, a fluid containing sperm, into the water, giving it a milky green or turquoise hue.

According to records from Fisheries and Oceans Canada (DFO), spawns near Forbes Island have been observed most years since the 1970s. Jessica Moffatt, a biologist with the Island Marine Aquatic Working Group (IMAWG), noted that herring prefer spawning sites with protection, rocky substrate, and reduced salinity, with Barkley Sound meeting many of these criteria. Other factors like collective memory and predation pressure also influence spawn size and location.

Spawning events can last from hours to days, with fish often arriving at the site weeks before actual spawning. In 2026, observers noted fish staging at Forbes Island by February 13, with spawning activity reported from February 19 to February 21.

Changes in water color during spawns often attract wildlife, including whales and sea lions in the water, and eagles, wolves, and bears on shore. After spawning, the herring return to deeper, nutrient-rich waters for summer feeding, sometimes staying together in the same large school for years.

Historically, spawn activity records have been limited by survey timing, remote location reports, and fisheries priorities. However, satellite observations like those from Landsat can help monitor herring activity across wider areas and longer periods. Researchers at the University of Victoria have used satellite data to enhance historical spawn records and develop methods for future detections.

Pacific herring and their roe are important culturally and commercially for First Nations and British Columbia’s fisheries. As a forage species, herring play a crucial role in supporting salmon and marine life. Understanding the locations of spawning areas can offer insights into changes in the marine ecosystem.

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Photos by Ryan Cutler. Story by Lindsey Doermann.