Researchers are trying to figure out a mystery: Why are so many humpback whales, right whales, and other large mammals dying along the U.S. East Coast? One possible explanation is a shift in food habits. And while theories are circulating that blame the growing offshore wind industry, scientists say there's no proof to support that idea.
Since Dec. 1, at least 18 reports have come in about large whales being washed ashore along the Atlantic Coast, according to the Marine Mammal Stranding Network. The losses are hitting populations that were already under watch, due to ongoing rises in unexpected deaths.
"Unfortunately, it's been a period of several years where we have had elevated strandings of large whales, but we are still concerned about this pulse" in deaths that's now been going on for weeks, as Sarah Wilkin, the coordinator for the Marine Mammal Health and Stranding Response Program, said on a recent call with journalists.
Scientists are particularly concerned about the recent spike in deaths, Wilkins said, because the increase is being seen in "a relatively tight geographic area," and over a short timeframe.
Here's a look at what's happening, and some of the possible reasons:
Which whale species are seeing spikes in deaths?
On the East Coast, two whale species — the humpback and the North Atlantic right whale — have each been suffering a spike in deaths over the past six or seven years, according to the National Oceanic and Atmospheric Administration.
The agency declared an unusual mortality event, or UME, for both types of whale. It defines a UME as an unexpected stranding that "involves a significant die-off of any marine mammal population" and requires an immediate response.
Since 2016, 180 humpbacks have been reported to be stranded on the coast of U.S. states from Florida to Maine. At least seven strandings have already been reported in 2023, including four in New Jersey — equaling the state's 2022 total.
For right whales, more than 20 percent of the population has been affected by the UME that's been documented since 2017, an alarming statistic for an endangered species that was last estimated to have 350 whales remaining. The UME figure includes whales that were found dead, injured, or ill.
On the West Coast, NOAA has been tracking a UME involving gray whales. Since early 2019, 303 gray whale strandings have been reported in the U.S. If Mexico and Canada are included, the overall number rises to 608. More than a third of those deaths occurred in the first year of the UME; the numbers have fallen sharply since.
All three of the whale species in question have previously been hunted close to extinction. And while the gray and humpback whales have rebounded, right whales remain an endangered species, with more deaths than births each year.
What about disruptions from offshore wind farms?
Even early in the unexpected humpback strandings, questions were being raised about the possible harm done to whales by wind farms. Those questions have grown during the current surge, as interest is surging in offshore wind energy projects that require using powerful devices to map the ocean floor.
The questions have only grown louder in the past two months, as crews perform surveys off of New York and New Jersey to learn details about the seafloor, both to learn where facilities could be located and where cables could be run.
The New Jersey-based group Clean Ocean Action has called for a halt to ocean wind projects and an investigation into the potential harm done to whales. Local and state officials have joined that effort, along with several members of Congress.
But officials from NOAA and other agencies are pushing back on suggestions that wind farms might somehow be contributing to whale deaths.
"There are no known connections between any of this offshore wind activity and any whale stranding regardless of species," Benjamin Laws, deputy chief for the permits and conservation division at NOAA Fisheries, said in a briefing call.
The kind of equipment being used in the area isn't as problematic as projects such as marine oil and gas exploration, said Erica Staaterman, a bioacoustician at the Bureau of Ocean Energy Management's Center for Marine Acoustics.
"Those in oil and gas are called seismic air guns, and they're specifically designed to penetrate kilometers into the seafloor. So they're very high energy, very loud sources," Staaterman said. In contrast, she added, the tools used to prepare for offshore wind sites are "high resolution geophysical sources, and they're typically smaller in the amount of acoustic energy they put into the water column."
"Many of them are used for very short periods of time with a long quiet time in between," Staaterman said, adding that some of the instruments also produce "a very narrow cone of sound," rather than blasting it in all directions.
"I just want to be unambiguous," Laws stated, "there is no information that would support any suggestion that any of the equipment that's being used in support of wind development [to perform surveys] could directly lead to the death of a whale."
So, what is killing the whales?
Overall, experts say that human interactions are a leading factor in whale deaths, through ship strikes or entanglements from ropes and other fishing gear.
That's a particular threat this winter, when animals that are typically the whales' prey have reportedly come close to shore, NOAA officials say. That shift leads humpbacks and other whales to follow along, creating more overlap where whales and ships share the same waters.
And as Wilkin notes, whale population growth could be a factor. "As whale abundance increases, we will get more whales in different places," she said.
For right whales, the agency says human interaction is the leading cause of death. Around half of the humpback whales that have died in the recent spike have had some level of necropsy exam, NOAA says. Of that number, about 40 percent showed evidence of a vessel strike or entanglement.
Causes of whale deaths can be determined in only a fraction of cases, partly because of the difficulty of examining a whale that dies in the wild, from their huge size to the various states of decomposition that might have occurred.
For the UME affecting gray whales in the Pacific Ocean, the cause is still undetermined, although researchers note that of the dead whales that were examined, several of them showed "evidence of emaciation."
One thing the ongoing UMEs on both sides of the coast have in common is their broad scale: While historically some UMEs have been very localized, tracking maps show that the humpback, gray and right whale strandings have happened up and down the Atlantic and Pacific coastlines.
That's a sharp contrast to previous clusters of deaths, like the 14 humpback whales that died from a biotoxin in 1987 — all of them in an area around Cape Cod, Mass. In that case, the deaths were attributed to saxitoxin, which is produced by red tide algae and can accumulate in mackerel — which the whales then eat.
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