We know next to nothing about some of the largest animals on the planet: the incredibly elusive beaked whales. But we could soon find out for the first time just how many species there are, by sequencing the DNA they leave in their wake.
can be up to 12 metres long but are hardly ever seen because they spend so much time deep underwater, sometimes diving to 3 kilometres. They also don’t survive in captivity.
There are 23 known species, including that has not been formally described.
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“There may still be some new species out there,” says of Hatfield Marine Science Center in Oregon. That’s because much of what we know comes from recordings of the sounds they make, which are thought to be unique to each species – yet some calls are not easily assigned to known species.
“Some of these species have never been seen alive,” says Baker. “We know they’re out there only from the strandings.”
DNA in that there water
Other kinds of whale spend more time at the surface. That means it is possible, if not easy, to get a small sample of cells for DNA sequencing,Ěýfor instance by firing a dart at them.
This just doesn’t work with beaked whales. “It’s simply a vanishingly unlikely option for some of these elusive, cryptic species,” says Baker.
But his team has now shown that if they can simply get close to beaked whales – for instance by listening for their calls – they can identify species from the DNA they leave behind in the water.
“It’s working well when we can put ourselves in the proximity of beaked whales,” says Baker. “Putting yourself where they were is not so difficult.”
Pretty leaky organisms
ł§±đ±çłÜ±đ˛Ôł¦ľ±˛Ô˛µĚýDNA in the environment, known as eDNA,Ěýis becoming common. However, Baker’s team is the first to show it can be used to identify large animals like whales in the open sea.
The whales’ DNA can be detected for up to two hours after the animals have swum through an area. It comes from the cells shed when they spout,Ěýdefecate or simply slough off old skin. “Whales are pretty leaky organisms,” says Baker.
So far, the team can sequence only the most common kind of DNA in cells, called mitochondrial DNA. This is enough to identify a species and some variation within a species, but not to identify individuals. However, the technology is advancing so fast that it might soon be possible to sequence the entire genome, which would reveal much more.
Baker’s team has not yet published their work on beaked whales, but they did publish a proof-of-principle study on killer whales in April (). It should be possible to use the technique to study any group of large marine animals, he says, from tuna to turtles and even sea birds.
