Humpback whales breaching in synchronicity off the coast of California near Monterey Bay may have been responding to a 4.7-magnitude earthquake, according to a local whale watching outfitter.

Photos captured on October 15 by Blue Ocean Whale Watch show a pair of humpback whales jumping out of the water. Strangely, onlookers noticed “distant whales in three different areas” breaching at the same time. It just so happened to correspond with a large earthquake that rattled Central California along the San Andreas Fault Line at 12.42pm local time, reported the US Geological Survey.

“Two distant pairs were double breaching and a single whale breached as well. Then suddenly the whales [we] were watching double-breached!” wrote Blue Ocean Whale Watch in a Facebook post. “We later found out this all happened at the same time as a 4.8 earthquake, whose epicenter was only 35 miles away, generated sound underwater in Monterey Bay.”

Kate Cummings, a whale-watching captain and owner of Blue Ocean Whale Watch, told IFLScience that she did not feel the earthquake while at sea but heard another captain over the marine radio say that there had been an earthquake at the moment she saw seven whales breaching within 6 kilometers (4 miles) of her boat for a total of about 10 minutes. 

"I knew earthquakes can generate sound underwater because a couple of diver friends of mine have been underwater at the time of the earthquake, so we all figured it was the sound that could have caused the whales to get so active suddenly," she told IFLScience. She noted that breaches are rare, double breaches even more so.  

"I am not saying with 100 percent certainty that these whales were breaching in reaction to the quake. But, I do think whales respond to sound and it's been proven there was a sudden spike in sound underwater that was picked up by a hydrophone at the exact same time the whales started breaching and I can't write it off as a coincidence," she said.

IFLScience also spoke with Alaska-based marine biologist Molly Zaleski who said that humpback whales do seem to be able to sense earthquakes.

“Most often, it seems whales’ reaction to earthquakes and tsunamis is to dive or put distance to try to avoid them,” she said, adding that it could be similar to how whales attempt to move away from seismic air guns. A 2016 study found that humpback whales are likely to move away from seismic surveys that involve “increasing the radiated sound level over 20-40 minutes,” but whether that has to do with the sound or the vessel emitting it remains unclear. Avoidance behavior in whales can result in stranding events. It is believed that noises created during seismic exploration may even increase the risk of narwhals dying in ice entrapment in the Arctic.   

Though the timing was “uncanny,” Blue Ocean Whale Watch is quick to add that it may have simply been a coincidence.

“Breaching is thought to be used to communicate with other whales, clean barnacles and other critters off their skin, and/or just have fun – which is probably more of an anthropomorphized answer,” explained Zaleski. 

Humpback whales are individually identifiable by the specific pattern on their fluke, akin to a human fingerprint, according to Ashley Blacow-Draeger, Pacific Policy and Communications Manager with Oceana. These charismatic, social giants can be found in the waters of Monterey Bay from April to November during their annual migration along western North America, one of the longest migrations of any mammal on the planet.

“Despite their large size, humpbacks feast on one of the ocean’s smallest food sources – krill, which are like tiny shrimp-like animals,” Blacow-Draeger told IFLScience. “Humpback whales can consume up to 3,000 pounds of food per day, of which krill is a significant portion.”

Entanglement in fishing gear and ship strikes are some of the most significant threats to humpbacks navigating ocean waters off the West Coast of the US, according to the National Oceanic and Atmospheric Administration (NOAA) Fisheries.