Unusual whale die-off is in its 2nd year, but cause remains a mystery

Using a tractor, state and town officials in coastal New Hampshire attempted to drop the carcass of a minke whale into a dumpster in mid-September. But the dead cetacean proved too big, bouncing off the red bin and flopping onto the pavement of a beachside parking lot.

The minke whale — which can weigh up to 20,000 pounds — is one of 55 that have turned up dead on East Coast shores of the United States since January 2017. 

The strange die-offs have officially been labeled as an “Unusual Mortality Event” (UME) by the National Oceanic and Atmospheric Administration (NOAA). The cause of whale deaths in this vastly-understudied species largely remain an inconsistent puzzle. 

“We have had 12 minke whales stranded in Massachusetts alone in 2018, so the numbers are still very high for this species,” Jennifer Goebel, NOAA’s public affairs officer in the Greater Atlantic Regional Fisheries Office, said via email.

A healthy minke whale.

But abundant minke whales aren’t the only Atlantic species dying strange deaths in high numbers. 

Both the famously charismatic humpbacks and endangered North Atlantic right whales are experiencing Unusual Mortality Events. Yet, there’s no clear link or commonalities between any of their deaths.

“We currently do not have one cause of stranding or death that is common across the three species involved in the different UMEs, additionally strandings across the three species are not clustering in space or time,” said Goebel.

Finding a clear cause for the spike in deaths of these wild seafaring animals is daunting. This year, scientists have performed 18 necropsies — examinations of corpses — on dead minke whales. 

“Final results are still pending for the majority of the cases,” noted Goebel, but eight are suspected to have died from an infectious disease, two appear to be have been struck by vessels, and nine show evidence of having been entangled in fishing lines. 

“These are the known deaths,” Tony LaCasse, a spokesperson for the New England Aquarium, said in an interview. The unknown deaths could be twice that number, he added.

Sleuthing out an explanation 

A notable problem in determining why minkes are experiencing such a mortality event is that the species, while known to be abundant in oceans globally, isn’t well understood.

“There is an absolute dearth of information on them,” Rachel Cartwright, a whale biologist at Cal State Channel Islands who has studied minke whales, said in an interview.

“They’re very understudied,” added LaCasse. “There’s literally nobody that I know of on the U.S. East Coast that studies these animals full time.”

Regardless, the health of baleen whales — who consume tiny fish and plankton — are visible indicators of greater problems in the seas.

“Baleen whales are recognized as indicator species,” said Cartwright. “They can tell you that there’s something larger amiss in the food chain.”

And although NOAA has been very clear that there’s presently still no smoking gun for these mortality events, “there’s speculation that there’s a disease element to this,” said LaCasse.

Fortunately for minkes, they’re an abundant, stable species — so they may withstand a bout of infectious, spreading disease. 

However, the same cannot be said of the 450 or so right whales remaining in the Atlantic.

The rise of minke whale deaths since Jan. 2017.

Weird things are also transpiring in the Pacific — though there’s certainly no evidence these disparate marine events are related.

Cartwright researches humpback populations that migrate between Hawaii and southeastern Alaska. They’ve experienced a recent, severe decline. 

“It’s an unusual time for a lot of whale populations,” she said. “Our populations in Hawaii have dropped dramatically in the last few years. Suffice to say, the mother and calves are going down by 80 percent.”

The humpbacks leave their winter Hawaiian breeding grounds to feed on fish in the frigid southeastern Alaskan waters. Typically, Cartwright observes plenty of calves there who have made the long journey with their mothers.

“This year we saw three,” said Cartwright.

Humpback whales are considered to be the most charismatic whale species.

In the Pacific Ocean, unusually warm waters due to a recent wide-scale marine heat wave may be to blame, noted Cartwright. 

This could have caused the food chain to crash and drive prey species well north — ultimately imperiling the vulnerable calves.   

But out on the East Coast, it appears the minkes have bounties of food.

“The minkes we’re seeing are often young and underweight, which is a little puzzling because there’s a lot of forage fish around,” said LaCasse. “They’ve [forage fish] been really exceptional near the shore.”

Whatever the ultimate cause of the Atlantic whale mortality events, the unusual deaths may very well be connected, and the dead whales are still coming ashore. 

“This event started in January 2017, and is continuing through today,” said Goebel.