Grey whale die-off pushes into second yr. Can the giants survive?

Worrying gray whale deaths along the Pacific coast two years ago appear to have continued into 2020, raising concerns that the ocean giants’ celebrated boom may not be safe.

Once near extinction, the whales are dying from a combination of killer whale attacks, ship attacks and starvation. Scientists aren’t sure why these hazards led to a sharp increase in deaths, but they believe this is related to disruptions in marine conditions caused by climate change.

As the whales swim past California this winter, marine biologists are watching an unprecedented migration between the Arctic and Mexico to see if the worrying trend will continue for another year. Some fear that ocean changes will pose an ever greater challenge to the cherished Titan, and could affect its future in the long term.

“We may have a few years where the death rate is lower,” said Pádraig Duignan, chief pathologist at the Marine Mammal Center in the Marin Headlands who performed necropsy of the whales. “But I expect such events to happen more often than in the past.”

In 2020, 172 whales were found washed up on beaches along the west coast of North America, according to the National Oceanic and Atmospheric Administration. 79 were in the United States, 88 in Mexico, and five in Canada. The numbers were only slightly lower than the 214 in 2019.

While some stranded whales are common during the annual whale migration, the recent numbers are not normal. For every whale found dead, the scientists estimate that five to ten more whales die unnoticed. Most sink to the bottom of the ocean or decompose without landing.

In 2019, when the surge in deaths was first observed, the National Oceanic and Atmospheric Administration declared an “Unusual Mortality Event,” a label that money and researchers pointed to the problem. A team of federal and academic investigators continues to try to learn more about why the whales are dying.

Gray whales were once common in the northern hemisphere. Today they are found in only two different population groups: a small group on the coasts of China, Korea and Russia and the recreational group that travels up and down the west coast every year.

Both populations were critically endangered a century ago, but international protection and the ban on commercial whaling are credited with saving the species. It is believed that the North American group has now grown to nearly 27,000 animals. The 50-foot beasts, which weigh 90,000 pounds and can live for 80 years, have become a popular spectacle for coastal visitors to the Bay Area.

The concern, however, is that increasing disruption to the marine environment could undo decades of progress.

“When the population changes, it can happen dramatically and quickly,” said Duignan. “The whales are fine now, but if something more drastic happens the population could crash.”

Observations and autopsies by Duignan and other scientists reveal a handful of causes of death for the whales. However, poor nutrition often underlies the animal’s condition, and when it did not result in death, it sometimes contributed to it.

For example, if a gray whale succumbs to a killer whale, it could be that the whale is not healthy enough to defend itself or its calf, Duignan said. A collision with a ship could be the result of a whale moving to new places to find food, such as San Francisco Bay, where it is more likely to be exposed to human activity.

This breach was discovered in 2017 by a gray whale just off the coast of Moss Beach on the coast of San Mateo County during a whale watching trip from Pillar Point Harbor in Half Moon Bay.

Chris Biertuempfel / Oceanic Society 2017

Most of the scientists’ observations and autopsies were conducted in 2019. The coronavirus pandemic limited research and collaboration over the past year. However, those involved in the work say their thinking stays the same: the whale’s poor health is likely linked to stress caused by the ocean caused by climate change.

The biggest problems are in the Arctic, where the whales spend their summers feeding.

There they rely on shrimp-like crustaceans known as amphipods, which they eat from the sea floor. However, these amphipods can become less numerous and less nutritious. The algae that the amphipods eat and that grow on sea ice before falling to the seabed become scarcer as the ice retreats in warmer temperatures. As a result, the amphipods are not as robust and the whales are not getting the meals they are used to.

Higher ocean temperatures in the Pacific have also changed the distribution of the whale’s other prey, which includes plankton, ghost shrimp and crab larvae, and fish that share their prey. Both affect a gray whale’s diet.

“Warmer water is generally not good for productivity,” said Sue Moore, a University of Washington scientist who studies whales in the Alaskan Arctic and is part of the team that studies deaths. “The (new) prey may have less fat and may be less nutritious. The whale’s body condition will show signs of it and if they are female they may not be able to give birth to a calf. “

The whales’ weakened condition also makes them more prone to disease, Moore said.

“Is that enough to trigger the (mortality) event? I don’t know, ”she said.

Fortunately, the whales are very resilient, added Moore. They are able to switch to new food sources and change their migrations to look for food. This helps them withstand the changing ocean and hold out on their 10,000 mile round trip that takes them back to the Baja California lagoons, where they give birth and spend part of the winter.

The deaths eerily resemble a spike in whale deaths two decades ago. In 1999 and 2000, more than 600 whales were reported stranded on the west coast. Scientists estimate that 20% of the total gray whale population has been lost. However, in 2001 the numbers stabilized and so far there has been no significant decrease.

John Calambokidis, senior research biologist at the Cascadia Research Collective in Olympia, Washington and part of the team studying whale deaths, says the current episode may just be another correction in the population.

“There are still many puzzles as to why we saw such a dramatic increase in mortality,” he said. “If we see mortality continuing into 2021, I will become increasingly concerned – and possibly alarmed.”

Kurtis Alexander is a contributor to the San Francisco Chronicle. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander