Nearly 1 in 5 Gray Whales Entering San Francisco Bay Die There, Study Finds
Researchers report that approximately 18 percent of photo-identified gray whales visiting San Francisco Bay from 2018 to 2025 died after entering the area. The deaths, often from vessel strikes, coincide with a population decline linked to reduced Arctic food availability. The findings highlight risks along the whales' migration route amid climate change.
Science NewsA study published on April 13, 2026, in Frontiers in Marine Science reveals that nearly 1 in 5 gray whales entering San Francisco Bay die there. Researchers analyzed 100,000 photos taken from 2018 to 2025 and identified 114 individual gray whales that visited the bay. Of these, 21 matched to documented carcasses, indicating an 18 percent mortality rate.
The study documented 70 gray whale carcasses in the region during the same period. Most of the remaining 49 carcasses were found in or near the bay, suggesting they also died after entering. Many carcasses were too decomposed for photo identification, so the actual rate may be higher.
Examination of the carcasses showed that vessel strikes caused nine of the 21 identified deaths and 30 of the 70 where a cause could be determined. Gray whales typically migrate 16,000 kilometers from Arctic feeding grounds to Mexico for mating and birthing, then return, without stopping in the bay.
Since 2018, some gray whales have begun entering San Francisco Bay, possibly to forage due to hunger.
This behavior started alongside a large die-off attributed to decreased food in the Arctic. A similar trend occurred in the late 1990s. The gray whale population has lost hundreds of individuals in recent years.
Researchers noted that the bay visits coincide with these losses along the migration route. Gray whales have also been spotted in unusual feeding areas off Florida, New England, and Hawaii. These explorations may indicate adaptation to changing conditions.
The pit stops in San Francisco Bay pose significant risks from ship traffic.
Protecting whales in these new areas could enhance population resilience to warming seas. However, climate change is altering historical migration patterns. Feeding in different areas might not fully compensate for Arctic food shortages.
