How do right whales find food? Scientists may be close to solving the mystery
North Atlantic right whales are among the most studied marine mammals on the planet. But scientists don’t know how the critically endangered whales find their food. CAI’s climate and environment reporter Eve Zuckoff recently spent a day on a research vessel in Cape Cod Bay with experts trying to solve that mystery. She joins us now to talk about what she saw. Hi Eve.
Patrick: Look, I know dolphins and other marine mammals use sound, or what’s known as echolocation, to find food. But how do whales do it?
Eve: Well, for baleen whales, which includes humpbacks, blue whales, and right whales, scientists have a hunch. They think that these whales are smelling a gas that’s emitted by plankton, which they eat. The gas is called dimethyl sulfide or DMS. And us humans can smell DMS, too. It’s that distinctive sulfury, salty air smell when you’re walking the beach or spending time around the sea.
So when I was aboard the research vessel, I talked to a scientist from the marine mammal remote sensing lab at the Woods Hole Oceanographic Institution named Hadley Clark. She explained how this chemical is linked to right whales.
Clark said: “So the food chain is: right whales eat zooplankton, zooplankton eat phytoplankton. And as zooplankton is eating phytoplankton, it releases DMS. And so we're looking for the right whales’ food’s food to see if they use smell to find their food."
So the key is to figure out whether there are links between high levels of DMS and high concentrations of right whales feeding in an area.
Patrick: But before scientists could do this research, they first had to find the whales. And there are only about 340 North Atlantic right whales left on the planet, so that’s no easy task. What was that like that day?
Eve: On the research boat, spotters climbed up a ladder to sit in a crow’s nest high above the water, and from hundreds of yards away they were seeing the whales’ spouts – these big misty exhalations – through binoculars.
It’s worth saying that tagging right whales isn’t a great option to find them because most fall off really quickly. So spotting whales by boat or plane is the best option. And ultimately, just two miles into Cape Cod Bay, we found a total of eight whales. One even popped up just 10 ft from the boat and we heard its big blow.
At one point, we saw whales eating, too. Right whales do what’s called “surface feeding.” They look like a slow-moving Pac-Man. With their heads all the way out of the water, they travel in a straight line with their mouths open. All the while, they’re taking in plankton and water, then filtering out what’s not food.
Clark told me: “They're trying to get all of the zooplankton in their path, and then they'll close their mouth and flush the water out. And then they’ll lick the zooplankton off of their baleen.”
We even saw a mother right whale with a calf swimming at her hip.
As Clark put it, “I mean, that’s the future of the population."
It was one of just about a dozen North Atlantic right whale babies born this year. So we saw something incredibly rare.
Patrick: Eve, once you found a whale, what would happen then? The scientists would jump into action, I guess.
Eve: Yes, so if we found a whale that was surface feeding, doing this Pac-Man thing, we’d get close to it, and then actually move several hundred feet away, repeating that cycle two or three times in a row to see how high the concentration of DMS is when we’re close to the whale, versus far from the whale.
To give you a sense, if you were looking at this pattern we were making in the boat from overhead it would look like we drew a flower. With the whale at the center, we were outlining the petals.
While this is happening, underneath the boat, a machine would be taking in water samples every seven minutes and measuring DMS levels.
Then the results would pop up on Clark’s laptop, and they seem to show what scientists were looking for. Hadley Clark has been on more than 10 research cruises like this in the last two years and she’s found that background levels of DMS in the ocean are from 5-10. Then higher levels are at around 12; that’s when scientists are starting to see whales in a given area. And when levels hit around 20, scientists are almost definitely seeing whales.
Patrick: But like all research, there are some limitations here, right? How do scientists know right whales aren’t finding food some other way?
Eve: It’s a fair question. And the research here is still preliminary. In fact, sometimes the DMS levels would stay practically the same for the entire time we saw a whale, whether we were five yards away or 500 yards away.
Now, part of that has to do with weather. On or right after bad weather days — with high winds, high waves — the DMS gets super mixed up in the water column so the data doesn’t offer much in the way of proving scientists’ hypothesis about the link between DMS and right whales.
But Clark said she still thinks there’s something here. Generally, the data is becoming more and more clear, and it’s buoyed by other research.
“Studies have been done with seabirds, actually, and that's where this hypothesis formulated,” Clark said. “They've done research where they have artificially released DMS into the air or into the ocean and predators come and aggregate around the release. … So they think that a lot of different sea creatures are using this DMS to find their food.”
Patrick: So Eve, what happens now with all this research?
Eve: All this research could help scientists build a predictive tool. They want to be able to know where these critically endangered right whales could be before they arrive, based on high DMS levels.
The way it stands now, officials have the power to close down some ocean areas to boat traffic when right whales are spotted. But that makes conservationists unhappy because it’s an imprecise system. You have to actually see right whales first, and by then it can be too late to prevent collisions with boats and entanglements in rope and fishing gear, which are the leading causes of deaths for the whales.
And it makes cargo, cruise and pleasure boat operators unhappy because they feel like important areas are being shut down without a complete understanding of right whale concentrations, which costs them money. So you could imagine this predictive tool could also be used in combination with an infrared camera that detects whale blows, to lead to even higher degrees of certainty about where whales are and will be.
In fact, Clark’s lab has the funding to build roving autonomous vehicles on which they could mount those cameras. Ultimately, the more tools we have to know if a right whale is present or not, the better for everyone.
Patrick: That’s CAI’s Eve Zuckoff. And we’ve got lots of great photos you shot while on board the research vessel on our website capeandislands.org Thank you,
Eve: Thanks, Patrick!