How melting Arctic sea ice is affecting the migration patterns of bowhead whales

Bowhead whales are an endangered species that spend their entire lives in the icy waters of the Arctic. They migrate north through the Bering Strait in the summer and fall to catch krill and other tiny crustaceans, and then travel south for the winter to the Bering Sea. But now, the rapid rate of melting Arctic sea ice due to climate change appears to be changing those migration patterns. Using 12 years of underwater recordings of bowhead whale songs, scientists at Oregon State University recently discovered that the whales have been delaying their migration through the Bering Strait in the fall, or opting to not pass through it at all during the winter months. Kate Stafford is an associate professor at the Oregon State University Marine Mammal Institute in Newport. She joins us to talk about the findings and what they mean for the health of bowhead whales, the ecology of the Arctic, and the Indigenous communities that embark on biannual whale hunts off the coast of Alaska.

This transcript was created by a computer and edited by a volunteer.

Dave Miller:  From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. Bowhead whales are an endangered species that spend their entire lives in the icy waters of the Arctic. But like many animals, they take part in seasonal migrations. The biggest group spends their winters in the Bering Sea, then heads even further north in the summers. But the timing and the patterns of these migrations seem to be changing, perhaps because of rapidly melting sea ice due to climate change. That is according to scientists at Oregon State University who collected underwater recordings of bowhead whale songs for 12 years. Kate Stafford is an Associate Professor at the Marine Mammal Institute in Newport and she joins us now. Welcome to Think Out Loud.

Kate Stafford:  Thanks, Dave. I’m very pleased to be here.

Miller:  What makes bowhead whales special or unique?

Stafford:  Well, as you said in the introduction, they are the whale that spends their entire life in the Arctic. I always tell people that, in my opinion, bowhead whales are a whale of superlatives. They’re the only Baleen whale to spend time in the Arctic year round.

Miller:  Can you remind us what that means? What’s a Baleen whale?

Stafford:  Oh yeah of course. There’s two types of whales. There’s whales with teeth in their mouth like killer whales or sperm whales. And then there’s whales like blue whales and humpbacks and bowheads that, instead of teeth, have these long plates of baleen, which is made of keratin, like our hair and fingernails. And the plates hang down from the roof of their mouth and they use those plates to filter their tiny prey. So bowhead whales for instance, feed on animals called copepods and krill. The copepods are about the size of a grain of rice and it’s these tiny little prey that are supporting these massive animals.

Miller:  But you mentioned that these are whales of superlatives - the most, the biggest, the best or whatever. So what are some of your other favorite superlatives about these whales?

Stafford:  Well, bowhead whales of course, because they live in the Arctic, they have the thickest blubber of any whale. They have the longest baleen. They can break ice up to a foot and a half thick. And what really impresses people is that they can live to be over 200 years old, which suggests that they’re the longest lived mammal.

Miller:  How have scientists been able to ascertain the ages of these whales?

Stafford:  Well, there are a number of lines of evidence for aging the whales. And I would say really the first line of evidence comes from traditional ecological knowledge. People who live with the bowhead whale, the Iñupiat, say that they live two human lives. And then because bowhead whales have been subject to both a commercial and very sustainable subsistence harvest, sometimes old harpoon heads are found in whales that have been taken and you can date those fairly accurately. And that’s told us that, in fact in the 2000′s, a harpoon head was found in a whale that had probably been put in that whale in an unsuccessful hunt in the 1800′s.

And then there’s a couple of chemical ways we can tell. Eye lenses have got this chemical in them called aspartic acid. And as an animal, including humans, ages the ratio of one kind of  aspartic acid changes in the eye. So you can use that to date whales. And then maybe the most interesting but potentially gross way you can do that is if you can extract the earwax from in a whale’s ear, much like trees grow rings every year, whales add a layer of earwax every year. So there’s a lot of different ways we know that they live 200 years.

Miller:  The age is adding an extra level of maybe sadness - is actually the right word - to the conversation we’re having here, which is about really rapid human-caused changes to our entire world and their entire world. It’s really striking to imagine a whale, right now that’s 200 years old, just in the last few decades, has been swimming through wildly changing waters?

Stafford:  Yeah, that’s actually a very good point Dave. And so the Arctic is warming roughly four times as fast as the rest of the globe. And one of the most obvious ways we see that is in this extreme decrease in sea ice, both the extent, the thickness and the age of sea ice. Bowheads are an ice whale. They spend their entire lives in the ice.

Miller:  What exactly did you set out to learn for this recent study?

Stafford:  Since about 2009, I’ve been putting hydrophones, which are underwater microphones, on an oceanographic mooring just north of Bering Strait and using that to listen to the soundscape year round. So how do sounds change over time throughout the year? And a post doc in my lab, who is the lead author of this study, Angela Szesciorka, took those data and started looking at them for bowhead whale song and bowhead whale calls to see if we could hear changes in the migration timing of bowheads. We have listened elsewhere in the arctic and found that bowheads have changed their migratory patterns out of the Beaufort Sea. But the question is, have they changed it through Bering Strait? The Bering Strait is a pinch point between Alaska and Russia. It’s the only gateway from the Pacific Ocean into the Arctic and, at its narrowest, it’s only about 55 miles wide. So populations of bowheads, belugas, bearded seals, walrus, they all migrate through this relatively narrow strait.

Miller:  So it’s a good place, if you’ve got microphones, to see if they’re there and when they’re there?

Stafford:  Exactly.

Miller:  Let’s have a listen to just one of, what I imagine is, thousands of hours of recordings that you and your group have put together? We’ll hear about 40 seconds of it.

(Bowhead whale sounds)

Miller:  Do you have a sense for, first of all, just how far away the whales might be from the underwater microphones, the hydrophones?

Stafford:  We’ve done a little bit of what’s called propagation loss modeling to determine how far away. And we think at most, we’re hearing these whales 20 miles away. But in general, probably much closer. One of the reasons we use passive acoustics, or we eavesdrop on the ocean, is that sound does travel much further underwater than it does in the air. So we can essentially census a wider area than we could if we were on a ship looking for whales.

Miller:  What might the whale, or whales, in that recording be saying or trying to communicate to one another?

Stafford:  Well, bowhead whales essentially make two different kinds of sounds. They make simple calls, which might sound like a whoop and those signals, which are primarily made year round, and they’re the only signals we hear in the summer and fall. And they’re used to maintain contact when migrating to navigate potentially to find food. What you just heard and what you just played was an example of a part of a bowhead song. So bowheads, in the winter, sing these elaborate ever changing songs, much like humpback whales do. And we think that these songs are likely male reproductive displays.

Miller:  So that would have been likely a call from a male to try to attract a mate?

Stafford:  Yeah, either to attract a mate by the females who can eavesdrop and decide hey I like your song best. I’d like to mate with you. Or potentially as male-male mediation. So that guy is saying hey listen to my song it’s louder, it’s longer, it’s more complex than yours.

Miller:  So don’t even try to sing because you know I’m the best singer here.

Stafford:  Exactly.

Miller:  Let’s get back to what you’ve been able to learn from these calls. How much are these whale migrations changing?

Stafford:  In fact, these whale’s migrations are changing by roughly six weeks a year if you think about it. So I talked about the Bering Strait earlier. And bowhead whales in the Western Arctic population, winter in the Northern Bering Sea. In the spring they migrate through Bering Strait along the west coast of Alaska and they head to the Canadian Beaufort Sea where they spend the summer feeding. Then in the fall they turn around and migrate back through the Bering Strait. What we found in this study is that bowhead whales are delaying their migration south from the Chukchi Sea into the Bering Sea by about three weeks. And in the spring when they migrate north they’re migrating about three weeks earlier. But probably more interestingly, in recent years, it looks like some portion of the population, and we don’t know which proportion of the population, is in fact not migrating south at all. They are spending the entire winter in the Chukchi Sea.

Miller:  They’re spending their entire lives, some of them, further north as opposed to ever going south. Why? What’s the mechanism that you’re assuming is behind this?

Stafford:  What Angela found was that it’s directly correlated to the sea ice extent in the area. So as I said earlier, sea ice has been changing dramatically, especially in the Chukchi Sea. And in years when there is less sea ice in the Chukchi Sea, bowhead whales migrate earlier and they stay later. When there is even less ice in the Bering Sea, that’s when the whales are spending all winter north of Bering Strait.

Miller:  Is there enough food for them if they don’t migrate?

Stafford:  Well that’s a really good question. I mean, they will still be migrating in the north. They’re just not migrating through Bering Strait, we think. And there is evidence that they do eat during the winter. They do eat under the ice. And right now the population of bowhead whales in our area, the Western Arctic population, seem to be doing pretty well. They do most of their feeding during the summer on lots of copepods and big swarms of krill. And so right now there seems to be enough food. Whether that will stay the case in the future, we don’t know. And this is one thing that’s sort of interesting but also a little bit frustrating. Things are changing so quickly that we don’t have a baseline to compare to anymore. Every year is different.

Miller:  I was curious about that. So even for the period of recordings that you looked at, from 2009 to 2021, how much has changed even just in that time?

Stafford:  Well, quite a bit has changed in that time. And in particular, starting in about 2017, there’s a fair bit of evidence that there has been a borealization of the Arctic, which is to say the entire community has been reorganized where arctic specialists are potentially being replaced by species that are more sub-arctic. And that includes fish, sea birds and it even includes whales. So, not part of this study, but another thing that we’ve been listening to on the same hydrophone are increases in sub-arctic whale species like killer whales, humpback whales and fin whales. They too are passing through Bering Strait.

Miller:  So what you’re describing is an entirely new or very new ecosystem with, as you said, no baseline, just changing year to year. It sounds both very interesting scientifically but also very challenging to track.

Stafford:  It is interesting scientifically, but it’s also kind of horrifying because things are changing so quickly. And the Arctic is a very unique ecosystem. It’s got endemic species that we don’t find anywhere else. And these are species that are either directly reliant on sea ice, like ice seals or polar bears and walrus, or species that are ice associated like bowhead whales and beluga whales and narwhals. So as we’re removing that habitat for these species, it’s hard to predict exactly how they are going to react and how the ecosystem will change for those species.

Miller:  What have these migratory changes in the loss of sea ice meant for Indigenous peoples in the Arctic, who as you noted, have had a long standing and sustainable fishery of these whales?

Stafford:  The bowhead whale is absolutely critical for nutritional, cultural and spiritual subsistence for the people who rely on bowheads. Bowheads have been hunted for millennia and people use them to bring together communities, to feed their families, to feed their communities. And so changes in bowhead distribution certainly has the potential to impact food security for Northern peoples.

There’s a very large island south of Bering Strait called St. Lawrence Island. And those hunters used to hunt bowhead primarily in the spring. Now, because of changing sea ice, they’re hunting more in fall and winter and they’re still being successful at hunting. But if all the bowhead whales in our western arctic population stopped migrating south into the Northern Bering Sea in winter, that means the bowheads will no longer be available to these people

Now that said, and of course bowhead whale migration is changing and people need to adapt to that, people have lived in the Arctic for millennia. You don’t survive in the Arctic without being incredibly flexible and adaptable. And so friends of mine who are Iñupiat eskimos have always said ‘we will adapt,’ and they will. The question is how and what role will the bowhead whale play in the future?

Miller:  What do you see as the biggest potential threats to bowhead whales going forward?

Stafford:  Well, in the Pacific arctic, there’s a number of threats. Certainly increased shipping through Bering Strait. Every ship that wants to go between the Pacific and the Arctic and take a shortcut has to pass through Bering Strait, which again is a very narrow strait. And even now there is commercial shipping in the middle of winter through Bering Strait because the sea ice is so thin. So ship strikes are a very real possibility. Increased predation from killer whales who are now moving further north and spending more time in the Arctic is certainly happening. And there’s competition as well from other sub-arctic species like fin whales and humpback whales.

And with the ocean warming, there’s always the potential for novel parasites and novel pathogens in the system.

Miller:  Has melting sea ice affected your ability to travel or travel at different times?

Stafford:  It has actually. So in some cases, we used to plan our research cruises into the Arctic based on what was called the open water season, which was the season when the Arctic was navigable for ships. Now, essentially, we can send a big ship into the Arctic anytime from June into November and even December. We don’t worry about ice anymore and we don’t really worry about ice taking out our instruments. I think since 2009 I’ve been going up onto the sea ice with my little hydrophone to get real time short term recordings of bowhead whales. And every year the ice is different and terrible in a different way. So there are times when it’s just not safe to be out on the ice getting recordings.

Miller:  What are you most interested in studying next?

Stafford:  What I’m most interested in studying next is singing behavior of bowhead whales and how that changes among the different populations of bowhead whales and who’s doing all the singing and why do we have so much variability? But what I’m spending a lot of time doing actually is listening to climate change and documenting changes in sub-arctic species like these humpback whales and killer whales that I’ve discussed. And I’m leading the really interesting stuff to Angela who’s doing amazing work as a post doc in my lab.

Miller:  Kate Stafford, thanks very much for your time today.

Stafford:  Thank you.

Miller:  Kate Stafford is an associate professor at OSU’s Marine Mammal Institute based in Newport. She joined us to talk about changes in the migration patterns of bowhead whales.

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