Gray whales starving, washing up dead in startling numbers along SF coast

TIBURON, CALIFORNIA - APRIL 23: Marine Mammal Center Director of Veterinary Science Dr. Pádraig J. Duignan stands on top of a beached grey whale as scientists and volunteers with the Marine Mammal Center and California Academy of Sciences perform a necropsy on the whale on April 23, 2019 in Tiburon, California. Scientists are studying the causes of death of 7 whales that have washed up on the shores of the San Francisco Bay and along the coast in the past month. It was determined that four of the whales died from malnutrition and three have died from ship strikes. (Photo by Justin Sullivan/Getty Images) less TIBURON, CALIFORNIA - APRIL 23: Marine Mammal Center Director of Veterinary Science Dr. Pádraig J. Duignan stands on top of a beached grey whale as scientists and volunteers with the Marine Mammal Center and ... more Photo: Justin Sullivan / Getty Images Photo: Justin Sullivan / Getty Images Image 1 of / 7 Caption Close Gray whales starving, washing up dead in startling numbers along SF coast 1 / 7 Back to Gallery

Exhausted, emaciated gray whales are going belly up along the coast of San Francisco this year at a rate seen only once — during a two-year period 20 years ago — since whaling was banned and the leviathans were pulled from the brink of extinction.

The death toll, part of a disturbing mass die-off from Mexico to Alaska, is happening largely because there is too little food in the ecosystem to sustain the behemoths on one of the world’s longest migrations, experts say.

The hulking carcasses of nine gray whales, several of them starving, have been found since March in San Francisco Bay and along the coast from Pacifica to Point Reyes. That’s an unusually large number for the region.

“It’s definitely not normal,” said Mary Jane Schramm, spokeswoman for the Greater Farallones National Marine Sanctuary, which has for decades been monitoring the spectacular whale migrations along the San Mateo, San Francisco, Marin and Sonoma county coasts.

The desperately hungry grays are taking dangerous detours into San Francisco Bay to look for food, a treat for whale watchers who have been seeing the gargantuan beasts in the estuary since February — but not such a good sign for those who care about their survival.

“They are attempting to forage in the bay’s ‘dire straits’ with their ship-strike risk, unknown toxins in the bay mud, and other threats,” Schramm said. “Some cannot make it any farther and are simply giving up the ghost.”

The strandings are happening along the entire coast of California, where 31 dead gray whales have been found this year, according to the National Marine Fisheries Service. In all, 48 gray whales have been found dead along the coasts of California, Washington, Oregon and Alaska, fisheries service officials said.

That’s not as bad as 1999, when 91 dead grays were recovered, or 2000, when 131 were found dead. But that die-off came in the wake of an unusually strong El Niño weather pattern that spread warm water along the entire West Coast and disrupted the food web.

There is a mild El Niño this year, and water temperatures are higher than normal, but marine biologists say the balmy conditions locally do not fully explain the increased death toll, which also rose the previous two years.

The cause of the decline, experts say, is an intricate and complicated cascade of events, including retreating polar ice, a lack of algae growth and a decline in the bottom-dwelling Arctic critters that gray whales eat.

“The majority of them have been skinnier, younger animals,” said Justin Viezbicke, the stranding coordinator for National Marine Fisheries Service in Long Beach. “I think the changing water conditions are what led to the changes in food.”

The trouble has not yet spread to other whale species, like humpbacks, which also migrate past San Francisco.

The difference is that eastern North Pacific gray whales are the only baleen whales that feed primarily on the bottom of the ocean. As such, they are considered by many scientists the sentinels of ecosystem change.

The Pacific grays feed in the shallow coastal shelf waters of the Arctic during the summer, where they scoop up mouthfuls of mud and siphon out benthic amphipods, tiny shrimp-like crustaceans, through their baleen.

The grayish barnacle-covered cetaceans, which can reach 45 feet in length, rely on the Arctic mud to supply them with enough calories for a 11,000-mile migration, the longest of any whale.

The remarkable journey starts when the grays head south from November to January toward the warm lagoons of Baja California, where they breed and give birth. The nursing mothers leave their breeding grounds and migrate with their calves north past California from February to May.

Photo: The Chronicle

It is a perilous journey for the creatures, which generally do not eat as they make a beeline toward the cold, food-rich waters of the north. The mothers use enormous amounts of energy nursing their calves, which can consume as much as 50 gallons of milk a day.

Scientists believe the trouble started under the Arctic ice pack. The tiny crustaceans that the gray whales eat rely on algae that grows on the underside of the ice. When that algae dies, it sinks to the seafloor, where the mud-dwelling critters feast. The less ice there is, the less algae and, consequently, fewer crustaceans. Which means less whale food.

Measurements taken by NASA’s snow and ice data center showed the ice coverage in 2018 was tied for the sixth-lowest summertime minimum in the satellite record dating back to 1979, well below what was normal between the 1970s and 1990s, according to Claire Parkinson, a climate change senior scientist at NASA’s Goddard Space Flight Center in Maryland.

Parkinson and her colleague Nick DiGirolamo calculated that sea ice has shrunk on average about 21,000 square miles each year since the late 1970s. That’s equivalent to losing a chunk of ice the size of Maryland and New Jersey combined every year for the past four decades, they said.

Scientists believe gray whales may be swimming farther to find less food, using up more energy.

Biologists monitoring the migration reported that 50% of the gray whales that arrived in Mexico last fall were already malnourished. The females also arrived later than usual to the lagoons and gave birth to fewer calves than normal, according to the annual assessment.

The constant stream of leviathans entering San Francisco Bay is a clear-cut sign all by itself that something is wrong, said Dr. Pádraig Duignan, the chief research pathologist at the Marine Mammal Center in the Marin Headlands.

The whales have been hanging out for long periods and feeding on bay mud, a highly abnormal practice for the species, he said.

Of the nine gray whale carcasses found in the Bay Area this year, six had entered San Francisco Bay, including a mother and calf seen recently trying to feed near the San Mateo Bridge. Four died of severe malnutrition, four after being hit by ships, and one found on the Point Reyes peninsula was too decomposed to tell what happened.

A necropsy performed Tuesday on a 41-foot female that washed up on Ocean Beach found injuries consistent with a ship strike, but Duignan said it also appeared to be malnourished.

“These mother whales are worn out and running on empty, making them even more susceptible to negative human interactions, including ship strikes and entanglements,” Duignan said.

It’s a troubling turn of events for gray whales, which rebounded after being hunted almost to extinction over the past 200 years. Fewer than 2,000 gray whales existed in the early 20th century.

International bans on commercial whaling in the 1930s and ’40s helped the species recover.

The last die-off, in 1999 and 2000, caused the population to decline about 30%, to about 18,000 animals. At least 40 of the 109 dead gray whales documented in California those two years were found on Bay Area beaches, local biologists and federal officials said.

With the population again recovered, there are now about 27,000 North Pacific grays, which is close to their historic population.

Viezbicke said there is a possibility that the gray whale population has simply reached its carrying capacity and is experiencing the kind of natural selection that every species on land or in the sea goes through when it outgrows its food supply.

“When you have a larger population, you would expect to see more strandings,” he said. “It’s definitely something we are going to monitor and watch, but we know the size of the population is robust.”

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com Twitter: @pfimrite