On Friday, a mass stranding of a reported 25 pilot whales was discovered beached on the shores of southern Norway, dead from unknown causes. The stranding went largely unnoticed in the news, marked only by a few stories days later on Norwegian news sites.
Workers on the ground are frantically trying to discover the cause of the incident and there are many potential reasons why a large pod of whales would beach. Dr. Darlene Ketten, a whale expert and neuroethologist, told The Dodo that this isn't so unusual - pilot whales have in fact been mass stranding for hundreds of years. They have the tendency to stick together, so when one whale strands, an entire pod usually comes along with him. It's possible that the whales followed prey into too-shallow waters, or the group followed a sick or injured member to shore.
"...This stranding could have been because of natural noise events - earthquakes, storms," Dr. Chris Parsons, marine mammal scientist and past president of the marine section of the Society for Conservation Biology, told The Dodo. He also suggested that confusion with coastal topography or disease in the "leader" pilot whales could be to blame.
"If the 'leader' gets disorientated because of parasites in brain or other disease, [she] may lead the group into dangerous shallow areas," he said, adding that calls from stranded individuals can draw others in, who also strand.
Another theory is the presence of nearby seismic testing and military sonar, which has been correlated to marine mammal strandings in the past. When intense pulses of sound are emitted into the water column during activities like naval war exercises or oil exploration, the acoustic waves can drive marine mammals to the shore, or even kill them at sea.
Without proper necropsies on the animals, however, it's nearly impossible to know if sonar or seismic testing were to blame. But, said Ken Balcomb, whale researcher and Executive Director of the Center for Whale Research, it can't be ruled out.
"Stuff happens; but, that does not mean that there was not a reasonable potential for seismic testing to be the cause," he told The Dodo in an email. He estimated that an acoustic blast at the level of 145 decibels would be enough to suspect seismic testing.
That's one theory that workers on the ground are looking into - but they will need to preserve the animals for necropsies to prove it. And even if they do preserve the bodies, it's difficult to prove causation, Balcomb, a former sonar officer in the U.S. Navy, said.
"The strandings are often a behavioral response to acoustic disturbance that might otherwise be sub-lethal, or result in temporary trauma."
According to footage taken by a bystander on the shore before the whales stranded, the animals were exhibiting "slightly odd behavior," according to Marit Borgan, a meteorologist who spoke to Norwegian news site Aftenposten. She said that several of the whales' heads were above water, and they were swimming around without direction. See video of the whales here.
For now, the cause of death for the 25 whales remains unknown. The Dodo has reached out to Norway's Ministry of Trade, Industry and Fisheries for more information and will update this post when we hear back.
UPDATE: - An interview with Dr. Chris Parsons has been added to this story.