On Monday morning, a female gray whale bearing signs of blunt force trauma washed up dead on the shores of Ocean Beach in San Francisco. It is the ninth gray whale to be found dead in the Bay area this year—a worrying trend that Pádraig Duignan, chief research pathologist at the Marine Mammal Center in California, calls “very unusual,” according to Kayla Epstein of the Washington Post.
“A normal year for us, we have maybe between one and three [dead] gray whales in this season,” Duignan tells Epstein. “This is triple that already, in less than a two-month period.”
The strandings have occurred within the past two months. After conducting an autopsy of the whale that was found this week, Marine Mammal Center experts concluded that the hulking creature had been killed by a ship strike; it had multiple fractures in its skull and upper vertebrae, with substantial bruising and hemorrhaging around the affected area, which is “consistent with blunt force trauma as a result of a ship strike,” according to a statement from the Marine Mammal Center.
Three of the other dead whales were hit by ships, according to the center, and the cause of death of one whale is not known. The remaining four whales died of malnutrition—and there were signs that things were not quite right with the most recently discovered gray whale, even before it was killed by a ship. “[The] team also noted that the whale was in poor body condition with a thinner than usual blubber layer,” the center explains in the statement.
Gray whales were once hunted to the brink of extinction, but they are now protected by international law and their population is considered stable. This year, however, scientists in California have noted that migrating gray whales seem to be in distress. Leila Miller of the Los Angeles Times reports that more than 30 dead gray whales have been seen along the West Coast since January, and that “dozens” of the animals are visibly malnourished. Sightings of mother-calf pairs have also declined.
The cause of the problem is not immediately clear, but the disruption of the whales’ food sources is a possible culprit. Each year, gray whales undertake the longest migration of any mammal on the planet. In the spring, they travel thousands of miles from the warm waters of Baja California, Mexico—where the mammals give birth to their calves during winter—up to the nutrient-rich waters of the North Pacific and Arctic. The whales do the bulk of their feeding during the summer months, building up the resources necessary to sustain them during the long migration back to Mexico, and then up again to colder waters.
“[A]ll their feeding is what is happening [in] the Arctic,” Duignan said, according to John Ramos of the local CBS SF Bay Area.
But the Arctic is highly vulnerable to climate change, which are already impacting gray whales’ ability to find food. “[C]limbing temperatures have begun melting ice that used to be impassable,” according to the Scripps Institution of Oceanography. “In the Arctic, this increases competition for food as more fish migrate through areas where gray whales historically feed upon crustaceans, plankton, and mollusks that they dredge from the ocean floor.”
There are indeed signs that gray whales haven’t been getting enough to eat during their summer feeding months in the Arctic. This spring, Epstein reports, scientists have seen the animals feeding in San Francisco Bay on their way north, which is not typical behavior and a possible indication that they have “have run out of fuel,” Duignan says. And the whales’ collision with ships may suggest that the creatures are moving closer to shore than they would otherwise, in an effort to find food.
This is not the first time that gray whales have been dying at an unsettling rate. Between 1999 and 2000, the species was struck by an “unusual mortality event,” and more than 600 strandings were documented along North America’s West Coast. The cause of the die-off is unknown, but starvation may have played a role.
Though this year’s gray whale deaths are not as numerous as they were some 20 years ago, Frances Gulland, a research associate at the UC Davis School of Veterinary Medicine, tells the L.A. Times' Miller that she fears as many as 70 gray whales may be found dead by the end of the season.
“If this continues at this pace through May,” Gulland says, “we would be alarmed.”