Cuvier’s beaked whales (Ziphius cavirostris) have just broken two mammalian records for dive depth and duration. These 20-feet, 5000-pound whales, with their pointy snouts, range from tropical to temperate seas, and because they prefer deep water habitat far from shore, they’re notoriously difficult to study. Shorter observations have shown that they can reach depths of 1888 meters (just over a mile) and stay below for 95 minutes, though the species remains poorly understood.
In the first long-term behavioral study of Cuvier’s beaked whales, a team led by Gregory Schorr of the Cascadia Research Collective in Olympia, Washington, tracked eight whales off the coast of southern California using satellite-linked tags pinned to their dorsal fins for periods of three months.
After sorting through 3732 hours of dive data, they discovered that one whale dove to depths of 2992 meters (that’s about 1.8 miles) below the surface. Another tagged whale remained below the surface for 2 hours, 17 minutes, 30 seconds. Both of these are new records for mammals.
"We were pretty surprised when we saw the data," study coauthor Erin Falcone of Cascadia Research tells Los Angeles Times. "We spent a little time making sure the tag was functioning properly just to be sure the data was right."
The previous deep-diving record holders were southern elephant seals, tracked to 2388 meters with the longest dive of 120 minutes. But unlike elephant seals and massive, deep-diving sperm whales -- which remain at the surface for an extended period after their dives -- the beaked whales could dive again in just two minutes. Although, usually they go for a single deep foraging dive, followed by a series of shallower ones.
The group’s average for deep dives was 1401 meters, with a duration of 67.4 minutes. They made their deep dives about seven times a day to hunt for squid and fish, spending more time at the surface at night. To help them hold their breath, they have a lot of the oxygen-binding protein myoglobin in their muscle tissue (so much, in fact, that their muscles look dark purple). These function like hemoglobin in blood, allowing them to store higher amounts of oxygen. To survive pressure changes during their dive, their lungs and trachea can collapse completely at depth, and then pop back open as they surface to breathe. "It is the presence of air spaces within the body that would crush a human at a fraction of the depths these whales can dive,” Falcone tells BBC. "Reduction in air spaces not only makes them more 'crush resistant,' but also likely serves to reduce the uptake of dissolved gases into their tissues,” which can lead to decompression sickness, otherwise known as “the bends.”
Another thing about beaked whales, they’re particularly sensitive to navy sonar, although scientists don’t know why. Of all the recorded marine mammal strandings associated with “mid-frequency active” sonar operations, beaked whales made up 69 percent. However, the whales in this study actually swam through a U.S. Navy sonar training range, suggesting that the whales have adapted to human noise -- perhaps by becoming such extreme divers. Though, the researchers urge against jumping to conclusions; they’re working on identifying behavioral changes during sonar exposure.
The findings were reported in PLOS ONE this week.
[Via Science, Los Angeles Times]
Image: Dan McSweeney / Cascadia Research
