Whales are changing where they feed due to climate change, according to Long Island-based research
Warming ocean waters are changing where whales and dolphins get their food, according to new research at Stony Brook University. J.D. Allen, host of WSHU's new climate podcast, Higher Ground, spoke with scientist Lesley Thorne about her research for the series. Now that it's published, he's following up.
J.D. Allen, WSHU: Lesley, your new study that shows some fish and squid are diving deeper into cooler waters doesn't work for whales.
In Episode 6, Higher Ground explored with Lesley Thorne why it is important to keep track of where whales feed and the impact climate change has on them, because humans might be hurting them.
Lesley Thorne: So unlike whales, which are air breathing vertebrates and have to return to the surface regularly to breathe, fish can stay underwater and can therefore seek out these different depths and stay at those deeper depths through time, whereas whales have to return regularly to the surface to breathe.
In the case of long-fin pilot whales, the species that we were studying, longfin pilot whales are capable of diving very deep in the water column, but they're actually quite short, on the order of about 15 minutes. We see that temperatures that are most important to their thermal budgets are actually surface temperatures, because they're spending more of their time proportionally at the surface, as opposed to at those deep depths that they go to for these quick foraging dives. And we looked at how its distribution had changed over a 25-year period, and also how the distribution of four of its most frequent prey species had changed, as well.
JDA: The whales have decided for the last 25 years to head north. Is that because they're following the movement of some of their other prey?
LT: The prey species actually didn't shift as far northward as far poleward as the whales, which is not really what we expected to see. So there's often, sort of, an assumption that whales are going to change and are going to move in relation to their prey.
Primarily, what we found actually suggests the opposite: that we see very rapid warming in the northwest Atlantic and particularly in the Gulf of Maine, in the Northeast of the U.S., very rapid warming. Other papers have found that this region is warming faster than 99% of the Earth's ocean surface.
JDA: Ninety-nine percent faster — how is any species supposed to keep up with that?
LT: Well, it seems that they respond in very different ways, depending on their thermal tolerances, depending on their distributions and their movement abilities. And what we saw was a range of different climate responses in the prey species. So one of the fish species did move northward. As temperatures shifted north and warmed in the Gulf of Maine in particular, we saw another species that shifted northward a bit, but also shifted into deeper offshore waters. And then we found two other species that shifted into deeper offshore waters.
So, we looked at all of these movements in relation to what we call climate velocity, which is describing essentially how quickly an animal would have to move in order to remain at a constant temperature. We actually found that the whales were moving faster than expected, based on that climate velocity.
Based on that physical change in the water temperature, but that the prey species were either moving as expected or slower in that northward direction. And again, we think that's because they were able to move deeper in the water column and therefore, experience cooler temperatures by going deeper rather than moving northward.
JDA: What does that tell you — when the climate velocity is different from the predator and the prey? They would probably need to be at the same rate if one's going to catch the other. But if they're moving at different rates, doesn't that interrupt how they feed?
LT: That's a great question in terms of how species are responding. And you know, what you'd expect is that most species would try to stay within thermal tolerance range, but what we actually see is that the relationships are more complicated than that.
So again, species are not all responding in the same way. And we think there are a lot of factors that could influence that, including different traits of species. So things like how long they can live, how big they are, their body size, the range of their distribution, their mobility, that influence how species respond to that changing water temperature.
JDA: When researchers publish studies, they hope that somebody that's reading it might build off of their work. So what do you hope is the next step in this research?
LT: There's a lot of interesting work that still to come and a lot that we still need to understand in terms of how species respond to climate change. We still don't know a lot about how many, many species respond. And that's particularly true for marine mammals.
So my lab is currently looking at responses of a range of different toothed whale species. And I think there's also a lot of work to be done in terms of understanding how species respond to temperatures at depth. So better understanding not just how surface temperatures are changing, which is sort of, you know, the easiest factor to look at when looking at some of these spatial shifts, but also understanding how temperatures at depth are changing and how species composition is changing as a whole. So instead of looking at species individually, understanding how predator prey dynamics, for example, are impacted when you've got species shifting at different rates.
Lesley Thorne is an assistant professor in the School of Marine and Atmospheric Sciences at Stony Brook University. Her findings are published in Scientific Reports.