Four dead gray whales have washed ashore beaches around the San Francisco Bay Area in the last nine days, NBC News reports

The recent string of deaths began on March 31 when a 41-foot adult female washed up on Crissy Field. A second female was found last Saturday in Moss Beach in San Mateo County. This week, a third whale was discovered at Berkeley Marina and a fourth was spotted on Muir Beach. 

While a few gray whales are normally found dead in or near the bay each year, this past week constitutes an unusual mortality event, defined by the National Oceanic and Atmospheric Administration (NOAA) as a significant die-off of a marine species. 

“It’s alarming to respond to four dead gray whales in just over a week because it really puts into perspective the current challenges faced by this species,” Dr. Pádraig Duignan, Director of Pathology at The Marine Mammal Center, told NBC News.

While the whale found Thursday died from a ship strike, experts haven’t determined how the other three whales died or if their deaths were due to starvation. 

In 2019, at least 13 dead whales washed ashore in the Bay Area. According to NBC News, Biologists have observed gray whales in poor body condition during their annual migration since 2019, when an “unusual mortality event” was declared by the National Oceanic and Atmospheric Administration.