Angel Island plays key role in study showing one in five gray whales entering SF Bay die

A remote beach on Angel Island, accessible only by boat, served as a staging ground for a landmark study that found at least one in five gray whales entering San Francisco Bay since 2018 has died there, with vessel strikes emerging as the leading killer.

The study, published April 13 in Frontiers in Marine Science, identified 114 gray whales in bay waters between 2018 and 2025 and matched 21 to carcasses — a minimum mortality rate of 18%.

The true figure is almost certainly higher, said Josephine Slaathaug, the study’s lead author and a Sonoma State University graduate student who studies gray whale health, identity and mortality in San Francisco Bay. She collaborated with researchers from the Sausalito-based Marine Mammal Center and the California Academy of Sciences in San Francisco.

Seventy gray whales were found dead in the same period. Scientists identified vessel-induced trauma and malnutrition linked to climate change’s effects on the animals’ migration as the leading causes of death.

At least six whales that entered bay waters in the past two months were later found dead. The pace of entries has been rising: 36 whales entered the bay in 2025 alone, sometimes more than 10 at a time — the most of any year in the study.

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