The mysterious Cuvier’s beaked whale is already known for its ability to dive to extreme depths, and now it has set a new record.
On Wednesday, scientists announced that the Cuvier’s broke the record for the deepest and longest dive of any mammal, descending to a depth of 9,816 feet (1.86 miles) and staying under for almost 2.5 hours.
The previous record was held by the southern elephant seal, set at 7,835 feet below the ocean surface and lasting for 120 minutes.
For the study, scientists fixed satellite tags to eight Cuvier’s whales off the Southern California coast. Researchers were amazed that the tags could even operate at such extreme depths.
“Our first step after receiving the record,” lead researcher Gregory Schorr from the Cascadia Research Collective said in an email to Business Insider,
“was to take the same type of tag and put it in a pressure tank to independently verify that the tag would indeed function that deep and report accurate values.” Lucky for them, it did!
The record-breaking dive was part of a larger study, published on Wednesday, March 26, in PLOS one, to better understand how the beaked whales’ deep-diving ability is affected by Naval sonar in the Southern California area.
“The causal link between sonar and strandings has not been definitively identified,” Schorr said, “but there has been speculation that beaked whales might be highly sensitive to sound in the same frequency band as sonar.”
The Cuvier’s makes up 69% of all marine mammal strandings associated with military sonar, according to a press release.
Sixty-eight nautical miles west from San Diego is the Southern California Anti-submarine Warfare Range. On the seafloor of this nearly 700-square mile training area are 172 underwater microphones that receive 3,408 hours of mid-frequency sonar a year broadcasted by the U.S. navy during training exercises.
These types of stranding events may be “more likely to involve deep-diving marine mammal species,” and to take place where the underwater landscape is complex and steep, according to NOAA.
If whales are in a canyon with a sonar-transmitting ship on the deeper end, the whales will move away from the sound source. In stranding cases, that may be the beach, said Schorr.
Based on location data, the whales were found in the sonar training range 38% of the time. However, it is still “highly likely sonar use in this area disturbs these whales,” Schorr said.
Because the team has not yet matched the exact times of sonar use with the locations and behaviours of the whales, it is tough to say for sure. This will be the team’s next step.
The study, which was co-authored by Erin Falcone, also of the Cascadia Research Collective, did still find new information. By keeping tags on eight whales for up to three months each, they recorded 3,732 hours worth of data.
“We were surprised by the broad variability both between and within individuals,” Schorr said. Previous studies had given the impression that the whales’ dive behaviours were patterned and predictable, Schorr said.
Out of the 6,827 recorded dives, almost 17% were classified as “deep dives.” These were longer dives related to foraging as determined by “the presence of echolocation clicks and/or evidence of prey chases,” the authors wrote in the paper.
The rest of the dives were shorter and shallower, lacking any evidence of hunting. The function of these dives is an area of “much speculation,” Schorr said. Given the great variation between individuals, Schorr speculates the shallow dives are possibly associated with avoiding predators, social behaviour, rest, or another unknown behaviour.
Also, unlike the elephant seal, the Cuvier’s does not appear to need long recovery times between deep dives, averaging less than two minutes at the surface between these dives, according to a press release.
Beaked whales, which make up about a quarter of all cetaceans (which includes whales, dolphins, and porpoises), are some of the most mysterious ocean mammals. They are difficult to sight due to their “cryptic, skittish behaviour, a low profile, and a small, inconspicuous blow on the waters surface,” according to NOAA.
Although the Cuvier’s is the most widely distributed of the beaked whales, they are difficult to study because they rarely breach the surface and inhabit deep waters far from shore.
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