Gray whale deaths in San Francisco Bay have risen sharply since 2018, with researchers documenting a surge in strandings that challenges long-held assumptions about the species’ migration patterns.
Scientists link the increase to changing ocean conditions and food scarcity
Josephine Slaathaug, who led a recent study on gray whale mortality in the bay, said that before 2018, gray whales were not known to stop seasonally or consistently in the 4,140-square-kilometre estuary, bypassing it on their migration route between Baja California and the Arctic.
The study found that altered sea temperatures and reduced availability of benthic amphipods—the whales’ primary food source—have forced some individuals to linger in the bay longer than usual, increasing their exposure to ship strikes and entanglement in fishing gear.
Local authorities respond with enhanced monitoring and mitigation efforts
In response to the trend, the National Oceanic and Atmospheric Administration (NOAA) has expanded aerial surveys and partnered with the San Francisco Bay Conservation and Development Commission to deploy real-time tracking buoys that alert vessels to whale presence.
Preliminary data from 2024 show a 15% reduction in reported ship strikes within the bay compared to 2022 levels, suggesting that early intervention measures are having a measurable impact.
Why are gray whales lingering in San Francisco Bay longer than before?
Scientists attribute the change to warming ocean temperatures and declining populations of benthic amphipods, which have made traditional feeding grounds less reliable and prompted some whales to seek alternative foraging areas in the bay.
What measures are being taken to reduce whale mortality in the bay?
NOAA has increased aerial surveillance, deployed real-time tracking buoys, and collaborated with local agencies to issue speed advisories for vessels in high-risk zones, efforts that have contributed to a preliminary 15% drop in ship strikes since 2022.