Studying what whales do underwater has always been hard, but thanks to new video and geolocation technology, scientists are now able to snag little glimpses of life beneath the sea and bring them to the surface.
And what they've seen can be surprising and delightful — like humpback whales exfoliating themselves on the shallow ocean floor.
"There was definitely no intention to capture whales rolling in sand," says Jan-Olaf Meynecke, who described the behavior in a recent paper in the Journal of Marine Science and Engineering. "The best thing about science is that you never know what you're actually looking for."
The new discovery reveals how innovative deployment of more precise instruments can help expand our understanding of elusive marine species. Behaviors once hidden from sight, like the humpbacks' "sand rolling," will help paint a more complex picture of their health needs and social life — and could help inform policy debates about offshore habitat conservation.
Meynecke did not set out to study cetacean skin care regimes. The marine scientist has been tracking the migrations of humpback whales since 2010, from his scientific home base at Griffith University in Brisbane, Australia.
It's difficult and expensive work, often requiring long hours in boats under rough conditions.
In 2019, Meynecke and his colleagues started attaching tracking tags called CATS cams to humpbacks for brief periods, as they swam along the Australian Gold Coast, either heading north to warmer tropical waters for breeding, or south toward the colder waters off Antarctica, where they feed.
At a basic level, the digital data prove that migrating whales don't travel in a straight line, coming up only to breathe or breach every once in a while. They're busy under the water, doing all sorts of mammalian things: courtship, friendship, fights over females, and simply hanging out.
"We've seen whales that are just, you know, swimming around each other," Meynecke says. "And they're in no rush because they're actually just spending some time together."
The tags can capture a humpback's fine-scale movements underwater, helping Meynecke and other researchers build a more accurate model of how the humpbacks backtrack, detour, and meander on their migrations. Through that, they can understand more about what habitats they frequent, and how much energy they spend along the way.
Meynecke explains that this research is critical because climate change will begin to impinge on their usual patterns: "The tropical waters will get too warm (above 28°C is not suitable for humpback whales) and Arctic waters will have less food to offer."
Meynecke is project manager for an international research consortium, the Whales and Climate Research Program.
It's serious, data-driven work. But in a serendipitous surprise, video footage from these digital trackers revealed a previously unknown new behavior: humpback whales rolling and rotating in the sand and gravel in Australia's Gold Coast Bay.
What were the humpbacks doing?
Although visually exciting, the video footage isn't the focus for this particular project. Meynecke referred to the footage as a useful "add-on" that helps verify the other data, such as the whale's speed and direction, and the depth and temperature of the water.
The team first caught the whales engaged in "sand rolling" while reviewing some footage from August 2021.
"I remember sitting there with my colleagues and we were laughing about it," says Meynecke, "Like, what? What are the whales doing? Like, why are they rolling on the sand?"
At first Meynecke wondered if the whale was trying to scrape the digital tag off of its dorsal fin. But the camera simultaneously captured another whale nearby, untagged, also spiraling through the sand. So it couldn't be that.
But what was it?
Video from two later expeditions also revealed humpbacks, both tagged and untagged, engaged in sand rolling.
Pieces of skin could be seen falling off the whales, and in some videos, fish known as silver trevally were observed eating the skin or darting in to pick skin directly off the whales.
The importance of skin care
The oceans are rich with microbes and parasites, as well as larger hitchhikers that ride on whales, like barnacles and remora suckerfish.
"One of the biggest problems for the whales is that there is constant shedding necessary, so that they can reduce infection from bacteria and viruses," Meynecke says.
Shedding of skin seems to increase as whales migrate between colder and warmer waters. So the sand rolling may be a way for humpbacks to actively speed up that exfoliating process.
But it may also help remove young barnacles from hard-to-reach skin crevices in the head region, according to Meynecke. In the sand rolls captured on video, the whales were "slowly moving forward with their head first into the sand followed by rolling to one side or a full roll."
One theory of why whales breach is that they're trying to knock excess barnacles off when they land. Sand rolling might be another technique, Meynecke says
"From my experience, the whales definitely don't want those barnacles on them," he says. "They're a burden when it comes to the dynamics. The swim speed is reduced and it's weighing them down."
Marine versus terrestrial mammals
Among terrestrial mammals — even the largest — scratching, rolling and other skin-care behaviors are well known, says Bruce Schulte, a biologist specializing in elephant behavior and conservation, and an associate vice president at Western Kentucky University.
"The epidermis is the largest organ that we have in the body. So you've got to take care of it," he says.
Elephants cope with insects like mites and ticks by water-bathing with their trunk, rubbing against trees, and rolling in mud. The layers of mud help prevent bites, and also shield them from sunburn, Schulte says. If mud isn't available, elephants, like many other species, will use dust — or add dust on top of the mud, to strengthen the coating.
Among marine mammals, orcas have been observed rubbing up against rocky beaches in the Pacific northwest, and bowhead whales "rock-nosing" in the eastern Canadian arctic.
Could whale spas enhance social relationships?
Sand rolling by humpbacks in deeper waters is a newer discovery, and could help inform what scientists know about their social needs, in addition to their health.
"They all were in a similar area where they were rolling," Meynecke says. "And it was always in a context of socializing as well. So they were not just doing it by themselves."
The cameras captured a courting male and female sand rolling together, as well as three bulls who went sand rolling after an hour-long fight over a female.
"It was a very severe, heavy fighting with ramming into each other. It looked definitely brutal."
Meynecke says if those three males sustained cuts or scrapes in the fight, then the sand rolling could help clean out the wounds. It's a theory, he says.
But the fact that the adversaries dove underwater and went sand rolling together is intriguing, he adds.
"If they have these fights, then it would make sense that they also have a reset moment," he says, especially considering that humpback whales are a highly social species, compared to other whales.
"It's not like that they're upset with each other for the rest of their lives," he says. "They keep seeing, you know, the same individuals and keep meeting up again over the years. So we're very certain that there [are] relationships amongst many, many of these individuals."
These discoveries help underscore that seemingly-simple behaviors can have multiple benefits, says Bruce Schulte, the elephant specialist.
"Does it start out, sort of evolutionarily...to make you feel better, to get parasites off, to make you healthier?" he asks.
"But then because there might be better areas to do this than others, does it also become a bit of a social event?"
Making the case for hygiene habitats
A mud wallow used by elephants, or a coastal area with the right kind of sand for exfoliation, and helpful fishes — these are habitats that may be just as crucial for species health as areas used for feeding, breeding and migrating.
"These types of discoveries, where we find areas that aren't used a lot, but they're used critically, are really important for understanding what we need to conserve," says Schulte.
Meynecke agrees, and notes that sand is a major global commodity, and Australia a major sand exporter.
In future research, he wants to continue to map the locations that whales use for sand rolling, to ensure that these "whale spas" are protected and preserved.
"If we started dredging sand in these areas or if we have a lot of boating activity, well, that means the whales can't go there or they won't go there," Meynecke says.
Copyright 2023 NPR. To see more, visit https://www.npr.org.
