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Consider the gray whale.
“Humans killed around 3 million whales in a period of like 70 years or so.”
In some species like the gray whale, certain populations dropped to just 5% of their historic
numbers. 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. 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 final record. And it folks said, "Wow, how could we possibly be killing these animals? We have to stop this." So that was in the 70s, that was sort of the birth of the modern conservation movement. 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.
“And then, hundreds of whales start washing up dead on beaches all along the west coast of”
the U.S. Canada and Mexico. The same thing happens the next year in 2000, hundreds more, wash up dead. 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." Everybody's wondering, "What caused this? We thought they were doing so well.
Has something changed? Are they on their way back down?" But then, the deaths stopped. The whale population recovered. Years on by and people moved on until a few years ago.
20 years later, 2019, hundreds of gray whales start washing up dead again. 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 SureWave, the science podcast from NPR.
This message comes from WISE, the app for international people using money around the globe. You can send, spend, and receive an up to 40 currencies with only a few simple taps. Be smart, get WISE, download the WISE app today or visit WISE.com to ease and seize apply. Okay, Josh, let's pick up this story.
“So we're in 2019, all of the whales are dying off again, then what happens?”
Yeah, so when you have hundreds of whales washed 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. What did you find? So we looked at this and basically what we found was that after the population had recovered to that sort of pre-wailing 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. Oh, wow.
And so you can have in this population alone 20 to 30 percent 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 percent 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 small critters that reproduce really quickly. It's not something that we expected to see in animals that live for 70 years. They're enormous. They take a really long time to reach sexual maturity, take a long time to reproduce.
There's not 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, this is a disease component that spreads and suddenly has a really strong impact
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.
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 didn't email from a colleague. What does she say? Yeah, so she, this is my colleague, Jackie Griebemeyer, 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. And so-- And it's the only time they're eating, like you're saying. Yeah, exactly. So that whole of their energy for the entire year depends on how many of these little critters
they can eat in that tiny window of 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.
So the claw machine? It looks like a claw machine. That's the prize is plankton.
“Well, yeah, a bunch of dirt is your prize.”
So she's been 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 never see that kind of like perfect alignment in your data.
And you know, on one sense, it's like magical because it's one of the coolest experiences you can have as a scientist. You don't have to even use any fancy statistics, although I love using fancy statistics, you can 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, 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 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 pre-limitation can be. Because again, you just don't expect to see that kind of response in the species like this. So this sounds like a natural cycle. Is that right?
Absolutely, yeah. So this is the interesting thing and where, you know, the story continues because we're
seeing this for the first time in gray whales.
But that was exactly my next question, which as well, is there anything surprising about
“this or is this exactly what we would expect to see?”
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 caring capacity and you've
run out of food and you're competing furiously with all of your, you know, they used to be your friends, but now they're your competitors. You're much more sensitive to those fluctuations in the environment. So if there's enough food for 25,000 whales and sometimes there's enough food for only 18,000 whales, if they're only 2,000 of you, you don't care.
There's plenty of food up there. So 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. So if this is a natural cycle, should humans do anything about this when they start
seeing whales just die? I know. So that's a good question. So the deeply unsatisfying part is that there's really probably nothing that we can do about 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 100s of whales wash up dead, we should just say, ah, no big deal. It's probably natural.
We still come back, they came back for we definitely still want to confirm 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 to... Well, in that plankton cycle may be affected by climate change, yeah, 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 av...
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. How long is it?
“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. So what are the larger lessons you think people should take away from this like whale mystery that you had a part in solving? Yeah, so there'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 the sort of, like we said, the unsatisfying thing is that there's not necessarily something we can do about that, except stop climate change. That would be great, but we haven't been very good at doing that yet.
“So it's going to be really hard, I think, for the public, for managers, for scientists,”
to deal with this when 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 going to be tough.
But they're kind of like the canary in the coal mine for climate change. Yeah, absolutely. I mean, I think that what we're seeing right now with gray whales is a climate alarm belief 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.
Josh, thank you so much for coming on shortwave to talk to us about whales. I'm glad you're a love whale. If you liked this episode, please share it with a friend. It really helps our show. To hear more ocean science, check out our C-Camp series, and it's a company newsletter
equipped with ocean critter pigs, deep dives into research and puzzles. We'll add links to our showdowns. This episode was produced by Burleigh McCoy, edited by our show winner Rebecca Ramirez and fact checked by Tyler Jones. The audio engineer was Jimmy Qley.
I'm Regina Barber, thank you for listening to Shortwave, from NPR.
