Two gray whales in the Pacific Coast Feeding Group are shown here in an undated provided photo. The whales, which spend the summer in the waters between Northern California and British Columbia, have been shrinking in size since about 2000.
Courtesy Oregon State University
A population of gray whales that feed off the Oregon coast have been shrinking in size over the last 20 years. New research from Oregon State University shows that whales born in 2020 are expected to be more than 13% shorter when full grown than whales born before 2000. The shrinkage could bring significant reproductive health challenges for the whales, and could also be a warning sign about the health of the broader ecosystem.
K.C. Bierlich is an assistant professor of senior research at OSU’s Marine Mammal Institute. He joins us with more details.
This transcript was created by a computer and edited by a volunteer.
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. We end today with some ominously shrinking whales. Researchers at Oregon State University have been focused on a population of gray whales that feed off the Oregon coast. They recently found that whales born in 2020 are expected to be 13% shorter when full grown than whales born before 2000. This shrinkage could bring significant reproductive health
challenges for the whales and it could be a warning sign about the health of the broader ecosystem. K.C. Bierlich is an assistant professor of senior research at OSU’s Marine Mammal Institute. He joins us now. Welcome to the show.
K.C. Bierlich: Hi, Dave. Thanks for having me.
Miller: Thanks for joining us. So this study is about a particular subset of gray whales that are found in the Northeastern Pacific Ocean. What is the Pacific Coast Feeding Group?
Bierlich: When we think of a typical gray whale, we’re referring to the Eastern North Pacific or ENP gray whale. Those gray whales spend their winters in Baja California, Mexico. Then they’ll migrate all the way up to the arctic Alaska to their summer feeding grounds and they’ll spend their summers up there eating constantly, getting nice and fat, and then use those fat reserves to then migrate back down to Mexico where they will breed and have their calves.
And instead, we have this really unusual group called the Pacific Coast Feeding Group that, instead of migrating all the way north like the normal typical ENP gray whale, they spend their summers between Northern California and Vancouver Island off British Columbia. Our team has been studying this group off the Oregon coast since 2016. Miller: Do you know why they have such different behaviors? Why they’re more or less resident?
Bierlich: Yeah, it’s a fascinating question and something we’re really interested in is why are they here? Why did they use this habitat? And it looks very different as you can imagine from the arctic summer grounds. I mean, if you go to the coast in Oregon, you can literally just stand on the cliffs and look down and see a gray whale right there ‒ which is pretty incredible to see ‒ a baleen whale so close to shore like that. And they’re swimming in shallow water. They’re swimming through kelp forests. Often they’re right up against the edge of a rock or a cliff and the waves are smashing against them, but they’re maintaining their position perfectly in place. So, they’re pretty incredible how they maneuver this complex coastline. And that’s been interesting to us because that’s a very different environment, that’s very different feeding behavior, than the ones in the arctic. And they’re feeding on different types of prey.
Something that we’ve discovered recently is we compared … so we use drones to fly over these whales and observe their behavior, and we can get measurements of them from the drones and look at their size, look at their body condition. And we were able to compare to the larger ENP, or that normal typical gray whale that goes to the Arctic. We found that these PCFG whales, they’re not only shorter, but they’re skinnier and they have smaller heads and smaller flukes. So it’s an interesting question of, we have a very different shaped gray whale here off the coast. Does that help them thrive in this very different environment? Or is this a warning sign that they’re not getting enough nutrients or something in there?
Miller: That was an earlier study that found the difference in size between the larger population that goes to the arctic and the one that sticks around the Oregon coast. But this new study found that, even among the local Pacific Coast Feeding Group, there is a pretty sizable change in size. That they’re getting 13% shorter. Can you put that 13% into human context?
Bierlich: Yeah, totally. And exactly, you nailed it. So, we first noticed these changes in size between the two different groups and then that led us to look more closely at have they always been smaller? And when did they start to get smaller? And we found since around 2000 they’ve been dropping in their size about 13%, which that’s pretty substantial. So we think about it from a human and the average American woman is about 5′4″. And so that means that we would expect her to be 4′8″ when she becomes an adult. For guys, typical 5′10″, you’d expect them to be 5′0″. So that’s a huge decline to consider.
Miller: Why is this a big deal? I mean, how might a gray whale’s health correlate to its size?
Bierlich: Size is really important. It tells you a lot about the animal; how it functions, how it thrives IN its environment, how healthy it is. And for an animal like a baleen whale, the size is critical because like I said earlier, they use these specific summer feeding grounds where they’ll migrate up to these areas that have a lot of productivity. They’ll feed constantly all summer and they get nice and fat. Then they use those fat reserves to help supply energy to them during their migration and during the winter when they’re breeding and producing calves. And they’re not feeding typically during those times, or feeding very little.
So they really rely on those fat reserves. So if a smaller whale is just gonna not be able to build up as large of fat reserves as a larger whale can. The big concern with that is, does a female who incurs more of the higher energetic cost to be able to supply enough energy or store enough energy, not only for herself, but for her calf ‒ to be able to produce a fetus, to be able to support a calf after it’s born ‒ is she actually going to be able to put on enough fat and supply enough energy to be able to support that calf and make sure it can actually grow? And so if that’s affecting reproduction, then now that actually might have consequences to the actual overall population.
Miller: And are males and females experiencing similar declines?
Bierlich: They both experience dramatic declines. But for females, it’s even more accelerated, and that’s what really has us concerned. Because again, like I said, since they incur more of that energetic cost, their decline is more rapid. For most baleen whale populations, there’s sexual dimorphism. So, the females are actually larger than the males. And again, I think that’s because, for one reason, they can store more energy to support them and the calf. What’s interesting now is, because the females and males have both declined in size in this PCFG population, but the females have declined at a faster rate, they’re actually now more equal in size. So we’ve kind of eliminated sexual dimorphism, which is a really interesting thing to observe.
Miller: And as you’re saying, may be problematic if that dimorphism is a result of millions of years of evolution that helped females nurse their young.
Bierlich: Exactly. Yeah, exactly. And in just a very short period of time, for such a long lived animal like a gray whale, to have had this drastic reduction in size in just 20 to 30 years, that’s kind of a red flag.
Miller: We mammals would certainly pay attention to it if in the course of 20 years, the average adult human height dropped that much.
Well, so let’s turn to the question of why. What are the leading hypotheses for what’s behind this?
Bierlich: We looked at some environmental variables and there was some correlations associated with this decline. And so specifically, the thing that kind of stands out the most is the Oregon Coast really benefits from this process of upwelling and relaxation. Upwelling basically is driven by winds on the surface, and it basically brings up nutrients from deeper water into the coastal areas. So it brings up these cold water and nutrients, and that helps bloom and helps productivity.
But importantly, following an upwelling event, you need these relaxation events where, once the nutrients get brought up into the shallower area, things kind of settle down so the nutrients can stay in place. And then things can really start to bloom and then prey will increase. That provides a lot of food for not only whales, but all sorts of other fish and mammals and birds.
So there’s been some other studies out of our lab that have shown that, when there’s this nice balance between upwelling and relaxation events, there’s more whales around and there’s actually more prey. And then when it gets out of balance, like let’s say there’s more upwelling and less relaxation, that’s when there’s maybe less whales around or less prey. So we saw a similar trend with the decrease in size. This decline in size is associated with getting away from that balance between upwelling and relaxation. So that’s kind of pointing to more environmentally-driven.
Miller: Does environmentally-driven mean led by climate change?
Bierlich: We can’t necessarily say that for sure. But it’s something to definitely keep an eye on. There are a lot of other factors that could be influencing this population. I mean, they are in very close coastal water, so they experience a lot of different stressors compared to other whales or compared to even the normal gray whales that go to the arctic. They’re surrounded by boats a lot, fishing boats, just commercial boats. They’re exposed to a lot of fishing gear in the water. There’s more pollution in the water. So there are a lot of other factors.
But we do know that oceans are changing and that is going to have a lot of consequences for the habitat. So that’s something that definitely we want to keep an eye on.
Miller: With these findings in mind … and it’s worth saying that this is such a short time period, which I guess works in two ways. One, you could say it’s such a dramatic change in such a short time here. The other is, it’s a relatively narrow set of data points. But given what you know now, would you argue that Pacific Coast whales should be managed differently than the larger population?
Bierlich: Yeah, that’s a great question, and I absolutely think so. It’s been fascinating, too, what we’ve learned about these whales in such a short period of time. And I think it really speaks to the technology and the innovative methods we have to use. We don’t actually know a lot about whales because they’re really challenging to study. You can’t just go out and ask a whale to hold still, and ask it how it’s doing, and take a tape measure and get some measurements. And that’s if you can even find it. A lot of times they’re out at sea. They spend very little time at the surface.
So the technology advances with using drones has just tremendously helped us. Being able to change our perspective to the sky, fly over these animals, get more details on them, be able to actually get accurate and precise measurements of their body shape and their body condition. And then working with other groups and scientists, and taking photos of whales, and being able to identify them by their unique markings. We see the same whales each year throughout the season, so we get to really know these whales and can understand their age. So it really speaks to all this technology that comes together to be able to do this sort of a study, to be able to look at these sort of trends.
Miller: K.C. Bierlich, thanks very much.
K.C. Bierlich: Yeah, thanks so much, Dave.
Miller: K.C. Bierlich is an assistant professor of senior research at OSU’s Marine Mammal Institute. He joined us to talk about their recent findings that a particular group of gray whales, a population that sticks around the Oregon coast, is expected to be 13% short of the ones who were born since 2020 than ones be born before 2000.
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