Scientists link herring spawn timing to shifts in grey whale northward movements

Panelists from Canada, Alaska and U.S. coastal programs said seasonal herring spawn plays a recurring role in where and when grey whales stop to feed during northward migration.

Aaron Foster (Fisheries and Oceans Canada) described ongoing work linking herring spawn timing to whale aggregation patterns off Vancouver Island, reporting that since 2019 large spring herring spawns have coincided with hundreds of animals feeding on eggs. "Some of the work John's group has done has identified from those photos we've collected, 30% PCFG feeding in the herring spawn and 70% non-PCFG," he said. That preliminary breakdown implies both locally resident PCFG whales and more northerly migrants exploit the resource.

Speakers said stable-isotope assays on skin and baleen can show herring-derived signals and that the isotope signature can appear within days of feeding but the turnover and persistence in different tissues (skin vs. baleen) varies and is not fully resolved. Panelists emphasized combining isotope results with photo-ID and drone photogrammetry to determine individual movement pathways and whether feeding stops are regular "pit stops" or responses to nutritional stress.