San Francisco Chronicle - (Sunday)
Scientists seek clues in deaths of 4 gray whales
Four dead gray whales have washed ashore in the Bay Area in the past week, prompting concern among scientists about the length and intensity of a dieoff of the giant mammals that is now in its third year.
The first whale carcass landed at San Francisco’s Crissy Field on March 31. Another was found in the Fitzgerald Marine Reserve at Moss Beach on Saturday. A third found floating in the bay was towed Wednesday to Angel Island, where staff from the Marine Mammal Center in Sausalito were to perform a necropsy Thursday morning when they got a call that a fourth had washed up on Muir Beach. On Friday, the Marine Mammal Center said a ship strike was the cause of death of the 41foot adult female found on Muir Beach. Scientists from the center and the California Academy of Sciences found signs of bluntforce trauma — hemorrhaging and bruising around the animal’s jaw and neck — typical of that kind of impact. They have not determined for certain the cause of death for the other animals, though a ship strike is also suspected for the one at Moss Beach. The deaths are part of a pattern seen before in a similar dieoff in 1999 and 2000. This one has lasted three years so far.
“Our team hasn’t responded to this number of dead gray whales in such a short span since 2019, when we performed a startling 13 necropsies in the San Francisco Bay Area,” said Dr. Pádraig Duignan, director of pathology at the Marine Mammal Center, in a statement. “Gray whales are ocean sentinels due to their adaptability and foraging habits, meaning they have a lot to tell us about the health of the ocean, so to see the species continue to suffer with the added threats of human interaction is a major cause for concern.”
The necropsy of the gray whale towed to Angel Island found it to be a young 37foot male that did not show signs of either a ship strike or malnutrition, the two main causes of gray whale deaths since 2019. The same was true for the animal that washed up on Crissy Field, the Marine Mammal Center said.
The risk of entanglement in crab fishing gear is also a concern, though more for humpback whales; no gray whales have died in crab fishing gear in California recently, according to the National Oceanic and Atmospheric Administration.
The current dieoff coincides with a recent pattern where gray whales have been spending unusually long periods in San Francisco Bay on their migration route from breeding grounds in Mexico to their feeding grounds in Alaska.
“Normally, in a regular year you’d see one or two gray whales that would poke into the bay for a little bit and then they would leave in a matter of hours,” said Bill Keener, research associate at the Marine Mammal Center. “That all changed in 2019, when we saw multiple gray whales — 10 to 15 — coming in and using San
“Our team hasn’t responded to this number of dead gray whales in such a short span since 2019, when we performed a startling 13 necropsies in the San Francisco Bay Area.”
Francisco Bay as a migratory stop or rest stop.” Some stayed for a whole month. When whales spend time in the bay, it puts them at greater risk of being hit by a ship, since the area is relatively small and ships don’t have much room to maneuver.
In addition, many of the whales coming through the area since 2019 have been extremely underweight, Keener said.
Gray whales aren’t at their fattest when they’re on the second leg of the 20,000mile journey from Alaska to Mexico and back without food, but these have had less blubber than usual. NOAA scientists are researching why they’re running out of food early in their migration, and there’s a suspicion it’s related to climate change.
Gray whales are bottom filter feeders, scooping up mud as they roll along the sea floor and sorting out crustaceans and other edibles through their baleen plates. One theory is that climate change is causing some of the sediment to move around.
Another theory is that as the whale population continues to increase, there hasn’t been enough food to go around in their feeding areas. Pacific gray whales are a success story overall, recovering from near extinction because of whaling after they were protected in the 1930s and ’40s.
The population that migrates off California also rebounded from the last “unusual mortality event” in 1999, as largescale dieoffs of marine mammals are called. It reached a population of 27,000, according to NOAA’s most recent count in 2016, which scientists estimate has since dropped by about onequarter because of recent dieoffs, Keener said.
For each whale that shows up dead on the beach, there are likely another 10 dead in the water, he said.
The whales typically leave the Bay Area by May, and Keener has no idea if the last four deaths are a blip or a part of an increasingly worse pattern. He just heard of another gray whale sighting in the bay Thursday.
“How many will show up dead along those shores we just don’t know,” Keener said, “but it definitely causes concern when they’re in the bay.”