The National Oceanic and Atmospheric Administration is investigating a die-off of West Coast gray whales that’s resulted in 70 known fatalities so far this year, including 13 animals whose enormous carcasses have been spotted off Bay Area shores, officials said Friday.
Declaring the whale deaths an “unusual mortality event” — a formal NOAA designation — will allow the federal agency to funnel more resources toward understanding the cause of the die-off and whether the West Coast gray whale population is at risk for further fatalities, perhaps due to climate change or other environmental conditions.
“This unexpected, significant die-off demands an immediate response,” Deborah Fauquier, a veterinary medical officer with NOAA’s Office of Protected Resources, said in a conference call with journalists on Friday.
The animal deaths have been occurring as the gray whales make their annual migration from the balmy waters off of Mexico, where they birth their calves, toward the chilly but bountiful feeding regions far north off Alaska. The last two carcasses to wash up in the Bay Area were reported May 23 — one near Angel Island in San Francisco Bay and the other on a beach in Point Reyes National Seashore.
In an average year, about 35 gray whale deaths are reported along the coasts of California, Oregon, Washington and Alaska, typically about 15 in the first five months, according to NOAA. The last major gray whale die-off was over a two-year period in 1999 and 2000, when almost a third of the total population is believed to have died. There were 222 documented gray whale deaths in those two years, including at least 40 in the Bay Area.
NOAA also launched an unusual mortality event investigation then, though scientists were never able to determine the cause of the deaths.
Many of the carcasses studied this year have appeared emaciated. The creatures may be starving to death or in such a weakened state that they are vulnerable to disease or man-made accidents like ship-strikes. Frequent sightings of the mammoths in San Francisco Bay and other inland areas suggest they are being forced to leave their normal migratory path to seek alternative food sources, scientists said.
Climate change could be changing or diminishing their natural nourishment, scientists have said. The massive whales — they can reach 45 feet in length and weigh up to 60,000 tons — may not be getting enough calories to survive the 11,000-mile migration from north to south and back north again.
But whether a scarcity of food or some other problem is to blame will likely be difficult to discern, scientists said Friday.
“It can take months to years to finally do the research to identify the cause. There may be multiple causes,” Fauquier said.
David Weller, a research wildlife biologist with NOAA’s Southwest Fisheries Science Center in the La Jolla area of San Diego, said history has shown that the gray whale population can recover from a season or two of increased fatalities. But scientists need more information about what’s happening to feel confident that there isn’t some dramatic environmental shift occurring that could cause long-term damage to the population.
“What we’re most interested in right now is examination of these individuals coming to shore to see how much we can learn from them — about their health and their condition,” Weller said.
Aside from climate change, another possible explanation is population size. The last count, from 2016, found 27,000 gray whales in the eastern North Pacific population. That’s around the size of peak populations in the 1980s, according to NOAA. It’s possible that this region of the Pacific Ocean simply can’t provide enough nourishment for a group that large and the population has reached what’s referred to as “carrying capacity.”
The formal investigation will begin with deeper analysis of the carcasses. Scientists will try to assess their age and sex, paying close attention to any trends. But marine mammal carcasses are notoriously difficult to study because they’re often badly decomposed by the time they’re discovered.
In fact, the reported gray whale deaths represent only a fraction — maybe 10 percent — of all fatalities, since in most cases the carcasses simply sink to the ocean floor.
“It’s very difficult to get to these whales in a timely fashion. So you can’t always get the kinds of samples you would need for diagnostic reasons,” said Sue Moore, a biological oceanographer at the University of Washington and a member of the event investigative team. “There are a lot of complicating factors.”
Erin Allday is a San Francisco Chronicle staff writer. Email: firstname.lastname@example.org
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