0:00:00.8 John Sheehan: California's gray whales are an iconic and beloved species, visible to spectators even from shore during their migrations.

0:00:08.1 Dr. Aimée Lang: The whales that feed up in the Arctic and sub-Arctic waters in the North Pacific then migrate all the way down the coast of North America to wintering grounds that are located in the lagoons and coastal waters of Baja, Mexico.

0:00:19.9 JS: But one population, the eastern North Pacific gray whale, has been of particular concern to NOAA scientists due to a recent UME, an unusual mortality event.

0:00:30.4 DL: That event lasted between 2019 to 2023. And during that time, the number of animals in the population decreased pretty markedly.

0:00:38.2 JS: This is Dive In with NOAA Fisheries. I'm John Sheehan. And today we'll get an update on the status of these gray whales. And hey, guess what? There is some good news.

0:00:47.5 DL: This most recent estimate from last winter actually represented an increase in the numbers compared to what we what we've been seeing during the UME So that was a good and positive sign for the population.

0:00:57.9 JS: This is my guest, Dr. Aimée Lang, a research biologist at NOAA's Southwest Fisheries Science Center and the lead author of a recent report on the annual calf count. As we'll hear, while this is a positive sign and the most recent unusual mortality event is over...

0:01:14.3 DL: It's a little bit complicated to evaluate what the current status of the population is relative to historic numbers, in part because there's a lot of uncertainty what those historic numbers were. But in general, we think that prior to the start of commercial whaling, there were probably around 20 to 25 thousand or so animals. So in general, I think the current numbers are approaching what we think of as healthy numbers, although the caveat is that that environment where they feed up in the Arctic is changing fairly rapidly. So the number of animals that environment can support is also changing. So we can't necessarily rely too heavily on past baselines to evaluate status. It's a bit of a moving target, but I think, you know, the take-home point is that the most recent numbers indicate an increase, and that's a positive sign for the population.

0:01:55.1 JS: Gotcha. And there's a lot to unpack there. But let's begin with sort of the top line, which is the population appears to be rebounding from previous years. That said, reproduction is lower.

0:02:07.4 DL: Correct. Calf production in the population was low from 2019 to 2023. We did see a slight bump up in the numbers in 2023, but this past year, calf production was back down to one of our lowest estimates of our time series, which, which dates back to 1994, so it's about a 30-year time series. So that's a little bit concerning, but I think it's not totally unexpected in that the increased mortality was determined to be associated with localized ecosystem changes on their subarctic and arctic feeding areas, so basically limitations in their access to and the quality and amount of their prey. And so you can imagine if you're a reproductive female, you've kind of been food stressed for, you know, three to four years now. It may be just take a while for these females to get back into good enough body condition to be back on kind of normal reproductive rates and producing calves. So we're hoping to see an increase in the calf production in upcoming years. Gray whales did actually go through an unusual mortality event previously in 1999 and 2000. And we saw that calf production during that event was low. And it did remain low the year after that event closed. But then the two years past that event, it had gone back to intermediate levels and then eventually reached higher levels. So we're hoping to see a similar pattern following this most recent UME.

0:03:24.8 JS: Okay. And could you remind us what an unusual mortality event is? And what are the sort of the conditions necessary to make a UME?

0:03:33.4 DL: So the official definition of an unusual mortality event, or a UME, is a stranding that is unexpected, involves a significant die-off of any marine mammal population, and demands an immediate response. For gray whales, basically the increase in strandings that we started to see in mid-December of 2018, we saw an increase in the number of gray whale stranding along the coast of North America. And so that met one of the criteria, which was there was a marked increase in the magnitude of mortalities compared to, to prior records or kind of normal years. And then the second criteria that was also met in the gray whales is that those stranded animals were exhibiting similar patterns. So in this case, many of the whales that stranded, not all of them, but many of them, appeared to be emaciated or in poor body condition. So that was kind of a commonality across many of the strandings.

0:04:22.1 JS: Got it. And you touched on this a little, but there was a period when their population was hit hard due to commercial whaling.

0:04:30.9 DL: There was. So, you know, like most baleen whales, gray whales on both sides of the North Pacific were greatly depleted by commercial whaling. Within the Eastern North Pacific, most of that depletion occurred in the mid to late 1800s. It started with ship-based whalers taking whales down in those lagoons off Mexico, which you can imagine offered a pretty easy opportunity to take whales. There was also some shore-based whaling that occurred mostly through northern Baja and off the coast of California. And that was taking place during the latter half of the 1800s to the early 1900s. And by that time, the population was depleted to the point where it really wasn't commercially viable to continue to take gray whales. But they didn't receive protection until the 1930s and more fully in the 1940s when the International Whaling Commission kind of got involved and countries signed on to cease commercial whaling along the range of the eastern North Pacific gray whales.

0:05:23.8 JS: And you mentioned they're baleen whales, so they kind of have that distinctive shape. Is there anything else about them visually that you can kind of just tell them apart?

0:05:31.2 DL: Yeah, I think gray whales are pretty distinctive visually. The thing that stands out most to me is their coloration pattern. They have this really beautiful kind of gray and white mottled color that is unlike any of the other baleen whales. So some of that white patterning that we see on the gray whales is due to scars from barnacles or interactions with killer whales or other things, but a lot of it is actual pigmentation that the gray whales are born with. And that's pretty unique or pretty interesting because it means even the very young calves that are born down in the lagoons, we can actually identify individuals based on that coloration pattern. So that's really just kind of a neat thing about gray whales is that we can track them from being very young calves throughout their life using these pigmentation patterns. And the other thing that I think is pretty notable about gray whales is that they do not have a dorsal fin.

0:06:17.0 DL: So, you know, most baleen whales have dorsal fins. Gray whales have what we call a dorsal hump, which is really just that. It's like a hump on their back where the dorsal fin would be, and that's followed by a series of dorsal ridges. And so in some whales, that dorsal hump and those ridges are pretty subtle, so it almost looks like the whale has a smooth back. In others, it's pretty marked, so you can really see pronounced ridges moving down the whale toward its tail. So that's pretty unique. Most other bailing whales have dorsal fins. The ones that don't, like bowheads and right whales, have different coloration patterns and are generally larger, so pretty easy to tell apart.

0:06:54.6 JS: Could I see one standing from shore?

0:06:57.0 DL: You absolutely could if you're in the right place. And I think that's one of the great things about gray whales is that they spend most of their life history quite close to shore. And so it is actually quite easy, if you know where to look, to go out and just stand along the coast and see gray whales migrating past.

0:07:12.2 JS: That's super cool. And that's one of the ways, at least, that you survey them is standing on shore and just counting them.

0:07:21.4 DL: It is. It's actually a really important part of how we study gray whales and why we've been able to study them so completely, because we can actually just sit on the shore in particular spots where we know they come particularly close to shore and count them as they migrate past. And so you can imagine that. It requires a lot less funding. It's easier to organize than trying to fund a ship-based survey that's got to go out in the water and track down the whales. So I think that's played a really important role in our ability to learn about this population.

0:07:49.3 JS: Yeah, but it still sounds pretty labor-intensive, at least from the... I mean, it sounds kind of like a stakeout. You've got a sort of setup shop, and you're not moving for a little while, right?

0:07:58.3 DL: That's true. So we do two surveys from the shore for gray whales, and both of them last between seven and nine weeks, depending on the timing of when the migration starts and so forth. And so for both those surveys, we have teams of observers that are basically sitting on the shore during all daylight hours and counting the whales as they pass by. So it's a fairly simple process, but it is, you know, it makes for some long days. You know, we take breaks in the middle to rest our eyes and so forth. And it's a team affair. We have a whole host of observers that contribute to this, many of which are from Southwest and do these counts year after year.

0:08:36.0 JS: What are the shifts like?

0:08:37.4 DL: A typical shift is about three hours long, and we work in teams of two, which is important because, you know, we're counting whales, and of course, everybody gets distracted at some point. So if you have two people out there watching and counting, you're much less likely to miss a group as it migrates past. And so we're basically, umm, for one of the surveys, we actually are sitting in a, a trailer that's on the coast because it's based up in the Carmel area, so it's... And it's in the winter. So it's a little windy, it's a little chilly. You know, you can get a little cold. So we're sitting in a trailer for a little bit of protection, counting the whales by eye or by handheld binoculars. So the whales are coming close enough to shore that we don't need any real specialized equipment to see them. And then we're logging those sightings into a computer program and keeping track of the whales as they migrate through.

0:09:24.5 JS: Got it. Are you taking like a snapshot of them, too, so you can sort of match them up later?

0:09:29.0 DL: We are not. And the reason we don't need to do that is because the gray whales are migrating for both these surveys. In the case of this survey near Carmel, they're consistently moving south. And so you can kind of track the groups as they move through the area without having to do some sort of individual identification. But that is a little tricky. It requires some expertise to kind of understand how fast gray whales move, how often they breathe, kind of what those patterns are. So it does take some expertise to kind of track that in your head that, you know, you see a group at the northernmost extent of the study area and then you're watching it as it moves south and to know which group you've already counted and which group you haven't. So that does require some expertise and we try and watch the whales through, you know, multiple sightings so we get a better idea of how many are in a group.

0:10:12.5 JS: And you must be pretty familiar with the groups now, too, and the individual whales. Like, "Oh, there's Jerry."

0:10:18.6 DL: That is true of other groups of gray whales. So there's two smaller groups of gray whales that feed, one in an area between northern California and southeastern Alaska, and the other in the western North Pacific, where... Those groups contain only about 200 to 300 whales. And we do know a lot of those whales by sight because you can see them over and over again. But when you think about this eastern North Pacific population, you know, in sort of normal years, that's about 20,000 whales. That's a lot to recognize by sight. So you might pick up on, "Hey, this group has a whale that's got a big white spot," or a white head. So you might be able to pick up on those little cues, but you don't necessarily know to the individual level.

0:11:00.0 JS: And we've kind of talked about how great it is that because they move so close to shore, you're able to gather so much information on them. You're able to track them consistently year over year. Can you talk about why it's so important to track them? What is the importance of keeping track of these gray whales?

0:11:18.2 DL: Well, I think the results of both these surveys of kind of tracking the abundance and the calf production in the population really plays into our understanding of the health of gray whales in the North Pacific. And so I think, I guess at the most basic level, the more we understand about gray whales and what impacts their population's health, the better job we can do to manage populations and, you know, where needed, put in place conservation actions to preserve them essentially so that future generations can, like I can, can go out to the coast of California and see the whales migrating past. So I think at the kind of basic level, that's really important. At a broader level, gray whales are considered to be a sentinel species for the Arctic. And that means that gray whale population health is essentially an indicator of the health of the environment in which they feed. So, you know, we have these long-term data series on gray whale abundance and calf production.

0:12:10.7 DL: And we've been able to put those into models that also include measures of environmental variability up in the Arctic, specifically sea ice and benthic prey availability. And those models have shown that they're linked, you know, that gray whale abundance and reproduction is correlated with sea ice and prey availability. So, kind of the cool thing about that is that we can sit, you know, onshore in California counting gray whales as they migrate past and get some indication of how healthy the Arctic environment is. So it doesn't mean that it's not important and critical to do, you know, more direct studies of environmental variation up in the Arctic, but it does mean that we have this really unique opportunity to get an idea of what's going on up in the Arctic by sitting in California counting whales.

0:12:49.4 JS: So given the recent status of the population abundance and reproduction for the gray whales, what is that telling you about the Arctic?

0:12:58.2 DL: I think it's telling us that it's changing, but gray whales in general, I would say, seem to be pretty flexible in adapting to those changes. So this recent UME is not the first time we've seen gray whales go through these cycles of decline and increase. So there was a similar decline in the mid-1980s. We don't have... Is good of records from back in that time. So we don't know if that was really associated with an increase in strandings, but it was a decline in abundance. Following that, the population increased and got back up to more normal numbers. Similarly, the previous UME, which was 1999 and 2000, population declined pretty markedly and then following it increased to more normal numbers until we hit this most recent UME And I think the concerning thing about the recent UME is that it was longer in duration than the previous event. So that was a little concerning and I think, you know, could have longer-term implications for the population. But in general, I think knowing what we know of gray whales' past recoveries from these events, I think there's reason to be cautiously optimistic they're going to recover from this event, both in terms of overall numbers and calf production.

0:14:06.6 DL: But, you know, it may take some time and we may be finding in the future that, you know, the Arctic may not be able to support as many gray whales as it used to. So that may be something we're going to end up finding out in the future, but it really... To me, it really highlights the value of doing these surveys and keeping track of the abundance in calf production in this population because we're learning a lot about how gray whales respond. And I think that provides information, like we discussed, about the health of the Arctic environment. But it also probably tells us a little bit about... On how other baleen whale populations are going to respond. And a lot of those populations are a lot harder to study. So it's kind of helping us understand this process of recovery and resilience to the changing environment and baleen whales more generally.

0:14:50.1 JS: Dr. Aimée Lang, thanks so much for talking with me.

0:14:52.5 DL: Thanks for having me. It was a really great discussion.

0:14:55.6 JS: Dr. Aimée Lang is a research biologist at NOAA's Southwest Fisheries Science Center and the lead author of a recent report of the annual calf count of the eastern North Pacific gray whale. You can find out more about gray whales, and learn how NOAA scientists are monitoring them now using advanced technologies such as infrared and unmanned systems in addition to visual observers; it’s all at our website, fisheries.noaa.gov. While you're there, you can even sign up for newsletters on any number of topics and really stay up to date. I'm John Sheehan, and this has been Dive In with NOAA Fisheries.