As California gray whale deaths mount, scientists raise alarm about ocean health

A dead gray whale that washed up this week on Limantour Beach at Point Reyes National Seashore is among a troubling wave of recent West Coast whale fatalities that coincides with migratory season, when the marine mammals make their way north to summer feeding grounds in the Arctic.

The journey marks an annual return from the warm-water lagoons and bays of Baja California, where calves are born during long months of fasting that precede the lengthy trip back north.

But disruptions in the food chain are preventing the whales from generating the blubber they need to endure the grueling 10,000-mile round trip, scientists say.

“Clearly something is going on with the forage, as these animals’ tanks of gas are either empty or very low,” said Justin Viezbicke, California marine mammal stranding coordinator for National Oceanic Atmospheric Administration.

The young whale that turned up Thursday on the south end of Limantour was the 13th gray whale to wash ashore dead in the greater Bay Area since March.

It appeared to be a recently weaned animal, and, from a photograph, “emaciated and malnourished,” though none of the experts had been out to see it yet, said Shawn Johnson, director of veterinary science for The Marine Mammal Center in Sausalito.

No necropsy had been scheduled by Friday evening, though a spokeswoman said someone from the facility would get out to take measurements and samples of the whale on Saturday, unless the tide took it back out to the ocean.

At least seven of the whales stranded in the area so far were found to be malnourished. At least five of the stranded whales had been struck by ships, four of them dying as a result, according to The Marine Mammal Center.

The known death toll for gray whales this season is 37 in California, where the annual average is 20 to 25, Viezbicke said. The combined total for California, Oregon and Washington is 61, on pace to match or exceed the record number of 86 deaths that occurred across the three states during the last big die-off in 2000, Viezbicke said.

The situation has become dire enough that Viezbicke said he expected his agency to formally declare an “unusual mortality event” next week, signaling a need to look at even wider implications for ocean health.

“There are more dead whales than there should be,” said UC Davis Research Associate Frances Gulland, a veterinarian and member of the U.S. Marine Mammal Commission. “It’s certainly enough to get one concerned about what’s going on in the feeding grounds.”

Among the factors scientists are contemplating are warming oceans and retreating ice shelves that appear to be driving gray whales farther north than they’ve historically gone for food. But there’s also the possibility that the so-called “warm blob,” a broad, persistent band of warm water that stretched down the coast from Alaska mostly in 2014 and ’15, had some ripple effect that is only now visible among the gray whales.

That would be similar to a large die-off among gray whales in 1999 and 2000, a few years after an intense El Niño period warmed Pacific waters, several said.

One-fifth of the gray whale population is estimated to have died during that time, said Gulland, who led the technical team that studied that event.

“It does seem like there is some lack of food thing going on, but it’s not 100% clear what is causing that,” said Elliott Hazen, a research ecologist with NOAA’s Southwest Fisheries Science Center. “Basically, is it long-term change? Is it still a repercussion of the warm water events we had in 2015? There’s not a clear smoking gun.”

Johnson said reports from Mexico this year indicated as many as 50% of the whales that arrived there last fall for the winter already were underweight.

There also were substantially fewer calves born during the whales’ time down south this year, Gulland said.

What’s also unusual is that gray whales, though known for traveling close to shore - making them a favorite of whale watchers - typically stay on course as they travel north.

This year, they’ve been wandering into places such as San Francisco Bay and the Strait of Juan De Fuca near Seattle, scientists said.

“They shouldn’t be coming inside,” Gulland said.

Several whales in February passed through the Golden Gate for weeks at a time Johnson said. They may have been hungry or too weak to withstand winter storms and were seeking shelter, he said. But they put themselves at increased risk of ship strike, already a deadly threat, he said.

Of the gray whales that have perished locally, all but five were stranded inside the bay. Two of have now washed ashore at Limantour Beach, including an adult female found April 30.

All but one was female, which makes sense since females and their young are the last to start the migration and, thus, have the least reserves as they start the journey. Females also impart a great deal of their energy to their calves during birth.

Hazen said it’s concerning that so many adults are among the dead, because they are usually “good at buffering against really bad conditions” by lowering reproductive rates for a few years until food supplies improve.

“When you start having adult mortalities, these large predators, it’s a sign they’ve been facing a number of bad years, most likely,” Hazen said. “I tend to view them as sentinels of ecosystem change for that reason. I do think they are telling us something.”

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.