Gray whale deaths lead to declaration of ‘unusual mortality event’

As more gray whales wash up dead on beaches in Puget Sound and along the West Coast, NOAA Fisheries has declared an “unusual mortality event” to mobilize additional research into what is killing these massive marine mammals.

Aerial images, such as this one off Central California, help biologists assess the condition of gray whales as part of a declared “unusual mortality event.”
Photo: Southwest Fisheries Science Center and SR3 under federal permits NMFS 19091 and MBNMS 2017-8.

About 70 gray whales have been found dead so far this year along the shorelines of California, Oregon, Washington and Alaska, with another 73 in Mexico and five in Canada. That’s the most since the year 2000, when more than 100 gray whales were stranded along the U.S. West Coast, triggering a previous unusual mortality event, or UME.

Many of the dead whales have shown signs of emaciation, suggesting that they failed to find enough food in the Arctic last summer, a time when they need to build up enough energy reserves to make it through the winter. Each year, the Eastern North Pacific gray whales travel from their feeding grounds in Alaska to their over-wintering areas in Mexico. As they return north at this time of year, they could be exhausting the remainder of their fat reserves, experts say.

A gray whale found dead at Washington state’s Leadbetter Point State Park near Long Beach was examined and found to be unusually thin.
Photo: John Weldon, Northern Oregon/Southern Washington Marine Mammal Stranding Program.

Not all the dead animals are showing signs of malnutrition. Other possible causes of death can include contaminants, environmental conditions, disease and being struck by moving ships. At least three of the animals were killed by ships.

The 70 whales found dead in U.S. waters this year compare to an average of 15 whales found stranded during the same January-through-May time period over the past 18 years. That number is just a fraction of the whales that actually died, however, since only 4 to 13 percent of dead gray whales are ever recovered, according to a study from the last UME.

For Washington state, the migration is about halfway through, while it is just beginning in Alaska, so officials predict that more gray whales will perish before they make it back to their feeding grounds. Of the 70 dead gray whales found on U.S. beaches so far, 37 stranded in California, 25 in Washington, five in Alaska and three in Oregon.

The total population of gray whales along the West Coast is estimated at 27,000, up from about 16,000 following the UME in 2000, when the population dropped by about 5,000 whales, according to Dave Weller, research wildlife biologist with NOAA’s Southwest Fisheries Science Center.

“We know the population can recover, given that all the other parameters remain the same, that the environment remain the same and there is enough food,” Weller said during a telephone news conference this afternoon.

“I would say that the number-one priority is learning as much as we can from the stranded animals,” he added. “Our monitoring will continue, and we will do another abundance estimate … and we’ll also be following calf production. We’ve got our finger on the pulse, and we will continue to monitor it closely.”

The number of calves born this year also appears to be down from average, as it has been in previous unusual mortality events. Whether feeding conditions will be better this year has not yet been determined.

Sue Moore, a biological oceanographer at the University of Washington, said gray whales eat a variety of things, and they can go where food is available. But conditions in the Arctic are changing rapidly, and it isn’t clear yet if they are eating amphipods — tiny shrimplike creatures that normally sustain them — or if they are shifting to other kinds of prey.

The sheer number of gray whales also may be a factor, in that their feeding areas could be reaching “carrying capacity” — although the experts stress that the number of whales that can be supported in the Arctic will vary, depending on environmental conditions that can increase or decrease prey populations.

“Carrying capacity varies by year,” said John Calambokidis, research biologist with Cascadia Research Collective in Olympia. “It certainly plays a role. How I would view it, too, is when animals are closer to the limits of the food supply is when you would start to see a portion of the population that isn’t as fit become more vulnerable.”

John noted that during these high-mortality incidents, more gray whales seem to come into Puget Sound and other busy estuaries, including San Francisco Bay. As a result, they are more likely to be hit by ships or become entangled in fishing nets.

Sue Moore said reports of deaths among other marine mammals, such as sea lions and walruses, will be investigated as part of the effort to understand the gray whale deaths and the overall ecosystem.

“In our investigation, we will bring in experts on gray whales, but we will bring in experts on the larger environment, and that includes other animals,” she said. “We do have some die-offs of birds along the California Coast, so we want to know if what is affecting the birds is different or the same as what is affecting the whales.”

Unusual mortality events can be declared by NOAA Fisheries when there is a significant die-off of any marine mammal species. In this case, the agency cited two of seven possible criteria used to declare a UME:

  • 1. A marked increase in the magnitude or a marked change in the nature of morbidity, mortality or strandings when compared with prior records, and
  • 5. Affected animals exhibit similar or unusual pathologic findings, behavior patterns, clinical signs, or general physical condition (e.g., blubber thickness).

The UME declaration can be used to mobilize a special UME Contingency Fund to reimburse people who officially help with the investigation. People may contribute to the fund or to local stranding networks on the NOAA Fisheries website.

Anyone who sees a dead, injured or stranded marine mammals is asked to call the West Coast Marine Mammal Stranding Network, (866) 767-6114. Only local and state officials and those authorized by NOAA Fisheries may legally handle live or dead marine mammals.

The annual gray whale migration — some 10,000 to 12,000 miles — is said to be the longest migration of any mammal. Adult grays can reach up to 46 feet long.

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