How do you count the world's most endangered whales? Expert shares how to estimate population size
The latest population estimate for North Atlantic right whales is out. Scientists say they’re hopeful a decade-long decline could finally be coming to an end. But to make that kind of determination, scientists first had to somehow count free-swimming whales in the ocean. Phillip Hamilton, a senior scientist the New England Aquarium, shared how that's possible with CAI’s Eve Zuckoff.
Eve Zuckoff: So we learned yesterday that the latest right whale population estimate is 356. What did you make of that number?
Philip Hamilton: Well, it's better than I anticipated. The population number has been going steadily down for around ten years now. And this is sort of a slowing down of the decline. The number actually still went down from last year. It went from 364 to 356, and there's margin of error on all those numbers. They're all estimated based upon the most data that we have available in any given year. But it's not as steep a decline. And I'm happy to see that. We're not out of the woods, but better than it could have been. Let's put it that way.
Eve Zuckoff: Scientists don't tag these animals to count them. Why is tagging right whales not a good option?
Philip Hamilton: Well, for a couple of reasons. One, it's a small population, so we actually know all of them by the photographs of their natural markings. So as far as making an accurate assessment of the population, tagging is definitely not necessary. There's been some interest in tagging recently to determine where all the whales are at any given time to avoid conflict with fisheries and vessel traffic. And that is really an untenable solution. The tags are harmful to the whales, to various degrees. You have to put them through their blubber and sometimes into their muscle. They last for a relatively short period of time and you're just going to have a very small sample size of a few whales traveling to certain areas.
Eve Zuckoff: So, Philip, how do you estimate the right whale population?
Philip Hamilton: Well, we have very, very detailed photographic information from all along the Eastern seaboard, which is basically the range of the species. So we're able to identify pretty much all the whales that we see, and we see very few whales in any given year that we haven't seen before. And they're mostly just calves.
So it's identifying those whales year after year. We get a count of those that are seen, and those data are then put into a model that the National Fisheries Service runs. It can estimate what the population number is, given the fact that we're not going to see every whale every year. We're not going to detect all the deaths. We may not detect all the births. So it allows for that uncertainty. But the core of it is just by knowing the individuals and seeing them year after year.
Eve Zuckoff: Our listeners may remember that the population estimate for 2021 was originally 340 whales. Then after recalculation, we learned over the weekend that it jumped to 364 that year. This is a population where every whale counts. How did that jump happen?
Philip Hamilton: I know it's really it's confusing to people and it takes a little while to answer that question. So the biggest part of this bump is because there was a relatively large number of calves born in 2021. We had 18 calves born. A lot of people say, 'Well, 18 calves were born. Why don't you just put them into the population?' And the reason we don't is because we have no way of actually tracking them. But we'll probably see those animals, you know, two or three years later with very distinctive identifying features. We'll say, 'Okay, this is a unique whale to the population.' So there's always a delay.
Eve Zuckoff: Philip Hamilton is a senior scientist at the New England Aquarium. Philip, thank you for joining us.
Philip Hamilton: Thank you. I really appreciate your interest.
This conversation has been edited for time and clarity.