Gray whales continue to wash up dead and emaciated, but causes remain elusive
The mass stranding of more than 50 gray whales at a San Francisco toothy beach last week was the second in as many years, and experts are searching for answers as to why.
Since the first such death in 2009 at Point Arena, on Cape Cod, a total of 58 gray whales have stranded in San Francisco Bay and waters off Marin and Sonoma counties.
The cause of death, according to experts and the public, remains elusive.
“There are no known causes of death,” said Dr. Peter Gleick, a marine biologist and author of “Wired for Sound: How Sonar Changed the World,” who was consulted for this story.
The whale deaths raise questions about the state of gray whale populations across the Bay Area, including in San Pablo Bay, and about whether they are being subjected to more pressure than any other population.
Gray whales typically make up about 30% of the North Pacific gray whale population, and are listed under the U.S. Endangered Species Act (ESA) as a critically endangered subpopulation.
The whale population in the Bay Area has been studied extensively since the 1950s, when scientists discovered that gray whales were being killed by motorboat propellers — a phenomenon they were not familiar with.
The whales have been subjected to fishing gear and the activities of commercial trawlers, and have been subject to incidental and direct capture by marine mammal protective organizations such as NOAA’s Marine Mammal Protection Alliance and the federal government’s Marine Mammal Rescue Program.
This is the first year since 2009 that a gray whale has died in the San Francisco area.
In 2008, a pregnant blue whale died off the coast of San Francisco during the winter, just over a month after another whale, probably adult, died in San Francisco Bay. This year, the two deaths appeared to be related, because a third whale was found dead in San Francisco Bay two days after the first and in the same location. But the cause of death wasn’t determined, and experts are still trying to solve the questions that are emerging.
“We didn’t know about the San Pablo Bay stranding until the whale was found dead,” said Gleick. “The whale had a tag, but the tag couldn’t tell us anything useful.