- For centuries, Japanese seafarers have noted two distinct types of pilot whale in their waters: One with a squarish head and dark body, the other a bit bigger with a round head and a light patch on its back.
- The two types have long been officially classified simply as forms of the same species, short-finned pilot whales (Globicephala macrorhynchus), but a new genetic study finds that they are actually distinct subspecies.
- The finding is just the latest shake-up of the cetacean family tree after the discoveries of new whale species in recent years.
- Mongabay spoke with the new study’s lead author, Amy Van Cise, a marine biologist at Woods Hole Oceanographic Institution in Massachusetts, about the science of whale taxonomy and what her team’s discovery means for the conservation of short-finned pilot whales.
For centuries, Japanese seafarers have noted two distinct types of pilot whale in their waters. One, known as Naisa goto, has a squarish head, an almost entirely dark body and lives in southern Japan; the other, known as Shiho goto, is a bit bigger, has a round head and a light patch on its back and lives in northern Japan.
The two types were first described scientifically in 1760, in a classic Japanese natural history of whales, but have long been officially classified simply as forms of the same species, short-finned pilot whales (Globicephala macrorhynchus). A genetic study published early this month finds that the two types are actually two distinct subspecies.
Short-finned pilot whales have been recognized as a single species, but a recent study found that two unique subspecies actually exist: the round-headed “Shiho” type, left, and the square-headed “Naisa” type, right. Image by Natalie Renier, Woods Hole Oceanographic Institution.
Moreover, while Naisa short-finned pilot whales live in tropical and temperate waters of the Atlantic and Indian oceans, in the Pacific they keep to the west while Shiho stay mainly in the east (plus northern Japan). It was the immense, food-poor expanse of the central Pacific that drove the two subspecies apart evolutionarily, the study authors contend, and not any obvious barrier like a continental landmass.
The finding is just the latest shake-up of the cetacean family tree. The discovery of several new species in recent years has prompted wonder that animals as large and captivating as whales and dolphins could elude discovery in the depths of the sea.
Mongabay spoke with the lead author of the new study, Amy Van Cise, a marine biologist at Woods Hole Oceanographic Institution in Massachusetts, about the science of whale taxonomy and what her team’s discovery means for the conservation of short-finned pilot whales.
Amy Van Cise. Image by Julia Fiedler.
Mongabay: Can you start by describing short-finned pilot whales?
Amy Van Cise: Sure. Short-finned pilot whales are actually not whales. They’re dolphins; they’re in the dolphin family [Delphinidae]. They’re the second-largest dolphins [after] the killer whale. And they look a little similar to killer whales. They’re very large. They don’t have any coloration the way killer whales do, so they’re just mostly a large black dolphin. They have a sister species called the long-finned pilot whale [G. melas].
Short-finned pilot whales are actually pretty understudied. There’s a lot that we don’t know about them. But there are some scientists who have done some pretty good studies on them more locally. For example, they know that a lot of these animals, at least in the more coastal populations, tend to prefer the slope region of the ocean. And that’s probably because they eat squid, and that’s squid [habitat]. They’re very deep-diving animals; they can [dive] up to 800 meters [2,620 feet].
I know some dolphin species like to ride boat wakes and they can be curious about people. What are short-finned pilot whales like, behaviorally?
The most notable characteristic about them is that they are very highly social. They always travel in these groups of like 30 or more. Those groups are very stable. A study that I did a couple years ago showed that those are actually immediate family members. There is a photo ID study that used 20 years of data and showed that the smallest groups spend nearly 100 percent of their time together; and those are immediate, like mom-dad-sister-brother, relationships. And then those small groups will sometimes meet up with other small groups and form a larger group [of 30 or more].
When you’re in a boat approaching these animals in the groups, they kind of are interacting amongst themselves and a lot of times they’re not really paying attention to the boat. That allows us a chance to observe their behaviors really closely and just watch them interact with each other, which is always really cool.
How do they interact with each other?
You see a lot of dyads, actually. Two animals tend to swim always right next to each other.
Are these mother-calf pairs?
We don’t know all the time what they are. Sometimes it is male dyads, so definitely not always mother-calf pairs. But they look to be socially stable dyads that continue for years and years and years.
We’ve [also] come upon groups [with] a really interesting group structure, where you get the large whales at the front and then all of the females and the young are kind of in the middle of the group. And then you get the two large males in the back, in what seems to be kind of a defensive type structure. I don’t think that we know much about them having any predators. It could be for something else, [such as] making sure the young don’t wander off and get lost.
Amy Van Cise, left, and colleague Annie Gorgone of the U.S. National Oceanographic and Atmospheric Administration photograph short-finned pilot whales in Hawaii. Image by Robin Baird, Cascadia Research Collective.
How did you get started on this question of short-finned pilot whales’ taxonomy?
There’s been this hypothesis in the general scientific community for quite some time now. Probably back in ’80s Japanese scientists started publishing papers showing that off the coast of Japan there were these two very different morphological types, groups of animals with very different body plans. Then, in the early 2000s another scientist started collecting some tissue samples. He was able to show that there was a genetic basis for the difference between these two groups and that it extends outside of Japan.
So that was kind of where we were when I was first introduced to short-finned pilot whales. The first study that I did [in 2016] looked at that genetic pattern throughout the entire Pacific Ocean and then a little bit in the Indian and Atlantic oceans as well. And we used a pretty simple genetic marker, but we found interesting and unexpected patterns in the way the animals were distributed. Everybody expected them to have a temperature-based distribution, so they expected to see a northern type and a southern type and that those two types would be kind of a cold water and a warm water [type]. But we didn’t find that at all. We found that there was a split down middle of the Pacific Ocean and there was an eastern type and a western type.
After we did that study we realized that we really should look more in depth to see just exactly how different these two types are and whether it’s a global pattern. And that was the basis of this study. So we sent an email out to the marine mammal [scientific] community and we asked for potential collaborators around the world to send us [tissue] samples of short-finned pilot whales. We got a lot of responses from areas where we didn’t previously have samples from, which was great. And so we were able to expand the study geographically to cover more of the range of these animals. We complemented our previous work with more technologically advanced [genetic] markers. Having the samples from a broader range really allowed us to say ‘now we know on a global level what’s happening with these animals.’ And that is one of the basic requirements of making a taxonomic recommendation, is that you have to be able to say that the pattern that you see is occurring throughout the entire global range of the species.
A Naisa type short-finned pilot whale. Image (c) 2019 S. Cerchio.
Your paper mentions that these two types of short-finned pilot whale were originally described in 1760, and of course they must have been known about locally much longer than that. Why did it take 260 years for taxonomy to catch up?
Basically in the early 1800s there was a great renaissance or blossoming of describing of species all over the world. And it happened for whales as well as a ton of other taxa. And so you just got naturalists and scientists all over the world separately and individually describing all these species. Short-finned pilot whales actually had upwards of 20 different species descriptions and different scientific names for these species. It was later, in the mid-1900s, when scientists started to look at all these and decided they’d gone too far, they’d named the species too many different times. And so for short-finned pilot whales along with a bunch of different species, they synonymized all these names and said ‘OK, all of these animals that we were considering to be 20 different species of short-finned pilot whale are just one.’
I think it was then that the information about these two different morphological types got lost. And then it was ‘rediscovered’ in the 1980s by these Japanese scientists who were working with Japanese whalers. The whalers, as far as I know, kind of always had that information. But it was just a matter of getting it to the scientists and then the scientists publishing it. It was something that the scientific community learned a second time, basically.
When you look at the pictures of them they look quite different. So it seems sort of intuitive that they should be split in that way. Is that being overly simplistic?
It’s a little bit. I don’t know if you necessarily want to call everything that looks a little bit different different. You might end up with just tons and tons of different species.
Which is what they did.
Yeah. There’s a really interesting debate in the taxonomy world. We have two different sides and we call them the splitters and the lumpers. And it’s actually kind of funny that geneticists usually fall among the splitters rather than the lumpers.
When you’re asking if two things are separate species or subspecies, at the species level you’re looking for a lack of mating in the wild. If in the wild, in their natural habitat, those two animals would not mate then we can call them different species. For the subspecies designation it’s a little more hazy, it’s a little more like can we show that these two animals are basically on two separate diverging evolutionary tracks, and that if left alone will become a separate species over time?
That’s a little bit difficult to prove. So we try to use sometimes a combination of morphology and genetics, and sometimes people look at other characteristics, like mating behaviors or feeding behaviors, to show that the animals are different. It usually ends up being a combination of multiple different data types to build a really strong argument.
A Shiho, top, and a Naisa short-finned pilot whale, bottom. Both types live in the Pacific Ocean, Naisa mainly in the west and Shiho mainly in the east (plus northern Japan). Naisa also live in the Atlantic and Indian oceans. Images courtesy of NOAA Southwest Fisheries Science Center (top) and Cascadia Research Collective (bottom).
Were there any surprises to you in this work?
I think probably the most surprising thing to me was that we didn’t get a third subspecies in the Atlantic Ocean. The only reason that surprised me is because I am human therefore I am kind of land-centric and I think of land as being this big important barrier to animals that are trying to travel around. And so I’m thinking ‘Oh well if we have two subspecies in the Pacific Ocean there’s clearly going to be a third subspecies in the Atlantic Ocean. But it turns out that that’s not true. There’s more migration and mixing happening around the southern tip of Africa than there is in the Pacific. To me that was the most interesting thing: that the middle of the Pacific, where it’s just this big barren food desert, is a greater barrier to these animals than the continent of Africa.
What are the conservation implications of there being two subspecies of short-finned pilot whale?
The fact that they’re considered one species globally means that they’re managed as such. But if there are two different subspecies of short-finned pilot whale, then management bodies are going to look at each of those subspecies differently. And that might change the way local populations are managed. In the United States we manage stocks of short-finned pilot whales in Hawaii, in the eastern Pacific off the coast of California and Oregon and Washington, and then in the Atlantic Ocean. In Hawaii the population estimate is in the neighborhood of 20,000 animals. So that seems to be a healthy population. In the California Current, on the other hand, the population estimate is somewhere around 500 animals. So if you consider the population a different subspecies than the one in Hawaii then you’re going to have to treat it differently from a conservation standpoint. You’re going to have to develop a management plan that’s suited to a population of 500 animals of the subspecies rather than two stocks of the same type of animal.
A Shiho type short-finned pilot whale. Image courtesy of NOAA Southwest Fisheries Science Center.
What kind of management questions would come into play?
The threats that they face are very local. In some areas there are hunts for pilot whales. Those are in Japan, the Faroe Islands, and then in some areas of the Caribbean. And there could be some hunts in the South Pacific as well. In the United States, with stocks that we manage, they can be caught in long-line fisheries. That happens off the coast of California and also off the coast of Hawaii. They seem to be sensitive to anthropogenic noise and navy sonar. They come in contact quite a bit with local tourism boats, but I’m not sure if that’s an actual threat for them. So I’d say fishing and noise are the two biggest [threats].
Short-finned pilot whales are a species that tend to strand in these large groups. So whenever you hear stories about a group of 30 or 50 or 100 animals that stranded on a beach somewhere, a lot of times that’s short-finned pilot whales. To my knowledge, nobody’s figured out yet why they strand the way they do. But when they do, you’re losing what seems to be basically an entire social group. If one animal in that group strands they all strand together.
There’s been a fair bit of juggling among cetacean species, like with the discovery of Omura’s whale [Balaenoptera omurai] and then a new kind of killer whale just a couple months ago. What does this all say about the state of our knowledge of whales? It’s kind of amazing that we’re finding these giant creatures that nobody knew about in the ocean.
The ocean is vast and incredibly understudied. We think we know a lot more about it than we actually do. There are all these places in the ocean where people really just haven’t been and haven’t looked. And, you know, the more you look the more you find. So I think that’s the first thing that’s happening.
The second thing that’s happening is just kind of an artifact of the way we’ve historically done science, which is that in order to describe a species you need to have a morphological specimen. And that usually ends up being a set of skull measurements or something very difficult to come by for animals that live out in the middle of the ocean where we don’t really have access to them. And on top of not really having access to them, we don’t really condone killing these animals for science. I don’t think we should be killing these animals for science either, [but] it makes it very difficult to get those skulls. And so that’s where genetics has come in and it’s just kind of opened up new worlds for us. Animals that we suspected were different species or different subspecies for a really long time, we’re now able to prove that they are.
Are there any key takeaways that you care to leave us with?
From a conservation standpoint I think it’s important to recognize different subspecies or species before you lose them. I think that as a society we would all be extremely sad to have lost a species simply because we didn’t recognize that it existed in the first place. Right now we’re racing against the clock for so many of these species and we’re just losing diversity right and left all around us. And those are the ones that we know about; at the same time there are probably all of these different subspecies and species that we don’t even know exist.
We can’t conserve what we don’t know. So if we’re going to try to properly conserve the biodiversity in the world around us we need to have an accurate picture of what that is.
This interview has been edited for length and clarity.
Van Cise, A.M., Baird, R.W., Baker, C.S., Cerchio, S., Claridge, D., Fielding, R., … & Oleson, E.M. (2019). Oceanographic barriers, divergence, and admixture: Phylogeography and taxonomy of two putative subspecies of short‐finned pilot whale. Molecular ecology.
Mahaffy, S.D., Baird, R.W., McSweeney, D.J., Webster, D.L., & Schorr, G.S. (2015). High site fidelity, strong associations, and long‐term bonds: Short‐finned pilot whales off the island of Hawai ‘i. Marine Mammal Science, 31(4), 1427-1451.
Van Cise, A.M., Martien, K.K., Mahaffy, S.D., Baird, R.W., Webster, D.L., Fowler, J.H., … & Morin, P.A. (2017). Familial social structure and socially driven genetic differentiation in Hawaiian short‐finned pilot whales. Molecular ecology, 26(23), 6730-6741.
Van Cise, A. M., Morin, P. A., Baird, R. W., Lang, A. R., Robertson, K. M., Chivers, S. J., … & Martien, K. K. (2016). Redrawing the map: mt DNA provides new insight into the distribution and diversity of short‐finned pilot whales in the Pacific Ocean. Marine Mammal Science, 32(4), 1177-1199.
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