We saved gray whales from extinction. Why are so many dying again?

In 1999 hundreds of gray whales washed up along the west coast of North America. More in 2000. They lost an estimated 25% of their population. But then the whale population recovered and people moved on. Until it happened again in 2019. And 2020, and 2021. It’s still happening today. Host Regina G. Barber https://www.npr.org/people/1082526815/regina-g-barber dives into this mystery with marine ecologist Joshua Stewart https://mmi.oregonstate.edu/people/joshua-stewart, who explains how scientists like himself solved it – and the tough questions that came up along the way. Check out our Sea Camp series https://www.npr.org/series/g-s1-75877/short-wave-sea-camp and our limited run Sea Camp newsletter https://www.npr.org/newsletter/sea-camp, featuring deep dives into research, cute critters and games! Interested in more ocean mysteries? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:12Regina Barber?

  You're listening to Short Wave from NPR.

• 0:18Regina Barber?

  Consider the gray whale.

• 0:20Speaker 02

  Humans killed around 3 million whales in a period of like 70 years or so.

• 0:27Regina Barber?

  In some species, like the gray whale, certain populations dropped to just 5% of their historic numbers.

• 0:34Speaker 02

  And we stopped hunting them pretty much because we'd killed so many of them that it was no longer economically viable to keep hunting them.

• 0:42Regina Barber?

  That's Joshua Stewart, a marine ecologist at Oregon State University. And he says along the way, the public took notice after a biologist and conservationist named Roger Payne put whale songs on a vinyl record.

• 1:00Speaker 02

  And folks said, wow, how could we possibly be killing these animals? We have to stop this.

• 1:09Speaker 02

  So that was in the 70s. That was sort of the birth of the modern conservation movement.

• 1:15Regina Barber?

  In the 1980s, the International Moratorium on Whaling went into effect and numbers started to climb. All the way through 1994, when numbers rebounded so much that the gray whale was officially removed from the endangered species list. But then 1999 happened.

• 1:36Speaker 02

  And then hundreds of whales start washing up dead on beaches all along the west coast of the US, Canada, and Mexico. The same thing happens the next year in 2000, hundreds more wash up dead.

• 1:48Regina Barber?

  And these are just the whales that people see, dead on the beach. It doesn't include the ones that die at sea during their more than 10,000 mile round trip migration to the Arctic. This is where they eat enough to last them the entire year. So Josh says scientists estimated thousands of whales died, accounting for about a quarter of the population.

• 2:09Speaker 02

  Everybody's wondering what caused this. We thought they were doing so well. Has something changed? Are they on their way back down?

• 2:18Regina Barber?

  But then the deaths stopped. The whale population recovered. Years went by and people moved on, until a few years ago.

• 2:27Speaker 02

  20 years later, 2019, hundreds of gray whales start washing up dead again.

• 2:33Regina Barber?

  And it's still happening today. Today on the show, a mass whale death mystery. How scientists figured it out and what it means for the species moving forward. I'm Regina Barber and you're listening to Short Wave, the science podcast from NPR.

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• 4:17Regina Barber?

  Okay, Josh, let's pick up this story. So we're in 2019, all of the whales are dying off again. Then what happens?

• 4:26Speaker 02

  Yeah, so when you have hundreds of whales wash up dead on a beach, people take notice. We have federal laws that are meant to protect and recover marine mammal populations. And so the government jumps into action in response to that. And they get these teams together of experts to try to understand what is driving these mortality events. And so I was part of that effort.

• 4:50Regina Barber?

  What did you find?

• 4:51Speaker 02

  So we looked at this, and basically what we found was that after the population had recovered to that sort of pre-whaling abundance or that carrying capacity, they're going through these cycles of booms and busts where it actually didn't just happen these two times in 1999 and then again in 2019. We found another major decline that happened 10 years before that in the 80s.

• 5:15Regina Barber?

  Oh, wow.

• 5:16Speaker 02

  And so you can have, in this population alone, 20 to 30% of the population die off in two, three, four years. And then in the past, it's turned around and recovered. And that, to me, is almost the more extraordinary part, that you can have this population recover that 20 or 30% also over a period of three to four years. It takes a little bit longer for them to recover than to die off. And so we're seeing these booms and busts, which you expect to see in short-lived, you know, small critters that reproduce really quickly. It's not something that we expected to see in animals.

• 5:53Regina Barber?

  These old whales.

• 5:54Speaker 02

  They live for, you know, 70 years, they're enormous, they take a really long time to reach sexual maturity, take a long time to reproduce. Those aren't really the patterns that you expect to see in an animal like that. And a lot of people, when they see that, they think, well, disease, you know, maybe this is a disease component that spreads and suddenly has a really strong impact and then maybe goes dormant for a while and comes back after a while. So there was a lot of emphasis, looking for disease as a potential driver as well.

• 6:22Regina Barber?

  Okay, so you're looking into this mystery, you find these cycles of boom and busts happening, and then a few years after these most recent mass die-offs, you get an email from a colleague. What does she say?

• 6:34Speaker 02

  Yeah, so she, this is my colleague Jackie Greedmeyer. She's an Arctic scientist and she studies the little critters, the crustaceans that live in the seafloor. And this is what gray whales migrate, all those thousands of kilometers to feed on every year.

• 6:49Regina Barber?

  And it's the only time they're eating, like you were saying?

• 6:52Speaker 02

  Yeah, exactly. So that whole, all of their energy for the entire year depends on how many of these little critters they can eat in that tiny window of, you know, three to five months in the summer. And so she's been going up to the Arctic on these cruises, collecting benthic grabs. They send a little claw down and it takes a sample of the mud and then they count everything in it. They weigh everything in it.

• 7:14Regina Barber?

  It's a claw machine?

• 7:15Speaker 02

  It looks like a claw-

• 7:16Regina Barber?

  That's the prize, is plankton?

• 7:18Speaker 02

  Well, yeah, a bunch of dirt is your prize. So, so she's been, you know, studying these critters and these ecosystems for decades. And so she sends me the data on how much benthic biomass, how much weight or average weight of these little crustaceans there are in the sediment. And I just roughly plot the data and the cycle that these little benthic crustaceans are showing perfectly aligns with these gray whale booms and busts. You, you never see that kind of like perfect alignment in, in your data.

• 7:52Regina Barber?

  Wow.

• 7:52Speaker 02

  And, and you know, on, on one sense, it's like magical because it's one of the coolest experiences you can have as a scientist to just, you don't have to even use any fancy statistics, although I love using fancy statistics. You could just see that in the raw data that these two things line up perfectly. So in that sense, it was super cool. On the other hand, it's so simple and obvious that the food that they migrate all this, you know, this way to go feed on is what's driving their population dynamics. Of course it is. You know, there's no surprise there. And so the, the surprise is not necessarily the drivers, which is how much food they have to eat and how long they have to access that food up in the Arctic. The surprise is how dramatic the response to that prey limitation

• 8:35Speaker 02

  can be. Cause again, you just don't expect to see that kind of response in a species like this.

• 8:40Regina Barber?

  So this sounds like a natural cycle. Is, is that right?

• 8:44Speaker 02

  Absolutely. Yeah. So this, this is the, the interesting thing and where, you know, the story continues because we're seeing this for the first time in, in gray whales. But- That was exactly my next question, which is, well, is there anything surprising about this, or is this exactly what we would expect to see?

• 9:03Regina Barber?

  Right.

• 9:04Speaker 02

  And what's unique about gray whales, in a sense, is just how well they've recovered. So they were one of the first whale populations or species to recover back to those levels that they were at before whaling. And so that is probably what triggered these events. And sort of our subsequent work that we've been doing is showing that actually, once you get to carrying capacity, and you've run out of food, and you're competing furiously with all of your, well, they used to be your friends, but now they're your competitors, you're much more sensitive to those fluctuations in the environment.

• 9:38Regina Barber?

  Oh, wow.

• 9:39Speaker 02

  So if there's enough food for 25,000 whales, and sometimes there's enough food for only 18,000 whales, if there are only 2,000 of you, you don't care. There's plenty of food up there. But once you're at that level, then those fluctuations start to matter. And so we only see these big booms and busts so far in these populations that have recovered up to those levels where they're really competing with each other for limited resources.

• 10:04Regina Barber?

  So if this is a natural cycle, should humans do anything about this when they start seeing whales just dying?

• 10:11Speaker 02

  Hmm, I know, it's so, that's, it's a good question. So the deeply unsatisfying part is that there's really probably nothing that we can do about the, you know, these natural cycles. So, once we find that, hey, this is driven by prey availability in the environment, there's not much more that we can do about that. Now, that doesn't mean that when hundreds of whales wash up dead, we should just say, ah, no big deal, you know, it's probably natural.

• 10:36Regina Barber?

  They'll come back.

• 10:38Speaker 02

  Yeah, they'll come back, they, they came back before. We definitely still want to confirm, you know, what is driving that die-off, because there are many other things that could be driving it. We, as humans, are increasing our footprint in the oceans, we fish more, we ship more things, we have tons-

• 10:56Regina Barber?

  Well, and that plankton cycle may be affected by-

• 10:59Speaker 02

  Climate change, yeah, uh-huh, that's a huge potential disruption. You know, we're moving out of a- Natural range of sort of variability and prey availability into this sort of new altered world where one of the biggest changes that we expect is just an overall reduction in the amount of plankton that's available on average. And so certainly we're seeing, I think that's what's happening in this most recent gray whale decline. It's much longer than previous boom.

• 11:30Regina Barber?

  How long is it?

• 11:31Speaker 02

  So this one has been going on pretty much nonstop since 2019. And the mortality rates have dropped off a little bit. Fewer whales are dying, but their birth rates have remained like rock bottom. So the population is not recovering the way that it did in previous years. And we're pretty sure that that is being driven by climate impacts to their Arctic feeding areas.

• 11:55Regina Barber?

  So what are the larger lessons you think people should take away from this like whale mystery that you had a part in solving?

• 12:03Speaker 02

  Yeah, so there's a it's sort of a paradox, which is that there are these populations that are doing extremely well. And so they've made these amazing recoveries. And we sort of thought, we don't have to worry about them anymore. But those are exactly the populations, because they've reached this point where they're competing with each other, that we're going to see these big responses to changes in the environment, natural variability in the environment, but especially climate impacts. Those are all going to show up first in these populations that we didn't think we needed to worry about anymore. And and the sort of like we said, the unsatisfying thing is that there's not necessarily something we can do about that, except, you know, stop

• 12:45Speaker 02

  climate change. That would be great. But we haven't been very good at doing that yet. So it's it's gonna be really hard, I think, for the public, for managers, for scientists to deal with this when, you know, we've been saying for years, look at these amazing, successful recoveries. And then it's those populations where it's like, well, what the heck? Why are hundreds of these whales washing up dead? And how do you say to the public at that point, oh, don't worry about it. There's nothing we can do. It's gonna be tough.

• 13:12Regina Barber?

  But they're kind of like the canary in the coal mine for for like Climate change.

• 13:16Speaker 02

  Yeah, absolutely. I mean, I think that what we're seeing right now with gray whales is a climate alarm bell because they're integrating what's happening in those ecosystems. It's easier for us to study what's going on with the gray whale population as they all migrate past us in California. It's much harder to have sort of a holistic assessment of what's happening in those really far-flung Arctic ecosystems. But yeah, we're getting that signal from gray whales that things are fundamentally changing. They're changing fast, and they're really being disrupted by these climate impacts.

• 13:53Regina Barber?

  Josh, thank you so much for coming on Short Wave to talk to us about whales.

• 13:57Speaker 02

  My pleasure. I love whales.

• 14:02Regina Barber?

  If you liked this episode, please share it with a friend. It really helps our show. To hear more ocean science, check out our Sea Camp series, and it's a company newsletter equipped with ocean critter pics, deep dives into research, and puzzles. We'll add links to our show notes.

• 14:20Regina Barber?

  This episode was produced by Burley McCoy, edited by our showrunner Rebecca Ramirez, and fact-checked by Tyler Jones. The audio engineer was Jimmy Keeley. I'm Regina Barber. Thank you for listening to Short Wave from NPR.

• 14:41Speaker 03

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