(majestic music) (water splashing) - [narrator] Humpback whales.

These charismatic mammals occur throughout the world's oceans (water spraying) and they have long fascinated those lucky enough to observe them.

(camera shutter clicking) (whales calling) - [anke] They have this really complex social system.

- [andy] They're quite intelligent critters.

- [rachel] The whale gives a feeling of the wildness of the world.

(whale thumping) (somber music) - [narrator] Once nearly hunted to extinction, these awe-inspiring animals have made a remarkable comeback since 1966, when the International Whaling Commission completed the global ban on commercial whaling of humpback whales.

- [martin] The North Pacific humpbacks, they were hunted quite heavily down to about 5% of the original population size.

- [andy] Some have estimated that there was about 1,200 to 1,400 individuals in the entire North Pacific.

- [marc] Humpback whale populations really were severely depleted, and it wasn't until they became protected through acts like the Marine Mammal Protection Act and the Endangered Species Act that we started to see a recovery of these populations.

(cheerful music) - [narrator] Since the 1970s, researchers have been studying the distinct humpback whale population that migrates between feeding grounds in southeast Alaska and breeding grounds in Hawai i.

With time, the numbers of animals steadily increased, and in 2004, a multi-year research effort involving more than 50 research groups got underway to determine the abundance of humpbacks throughout the North Pacific.

- [adam] It was estimated that there was a little over 10,000 whales now visiting Hawai i.

Now from less than a thousand in the 1970s to over 10,000 in 2006, and that was from a population North Pacific wide of about 21,000 whales.

That's an incredible recovery story.

The rate of annual abundance increase was about 6 to 7%.

(low urgent music) - [narrator] Based on this assessment and others, the National Oceanic and Atmospheric Administration removed the Hawai i distinct population segment of humpback whales from the U.S. endangered species list in 2016.

- [lars] It's not very often that we see these conservation successes.

So that's an example of us doing something right in nature.

(water spraying) - [joe] So people are breathing a sigh of relief thinking they're out of the woods.

- [narrator] But the celebration of this incredible conservation success story was short-lived.

- [eden] In the 2015/2016 whale season here in Hawai i, we started to get anecdotal reports that whale numbers were lower than usual.

So initially we thought maybe there's just a late arrival, could be patchy distribution, not really sure, but that trend continued for the next three seasons.

(camera shutter clicking) - [andy] We started seeing fewer whales here in Alaska, far fewer calves than we had seen in previous years, we're seeing more whales apparently that and we're seeing a lot more skinny and emaciated whales.

- [marc] It came as a big shock because the humpback whale population had been recovering so steadily.

All of us really were caught off guard and we just didn't know what to think.

- [adam] It was a major concern.

You can't help but be impacted emotionally.

(water spraying) (plane engine whirring) - [joe] People think of scientists as being kind of all head and no heart, but no, it's quite different.

(fin thuds) After you've been studying the species for a while, it becomes a personal involvement.

- [adam] If they're missing, it's like losing a family member.

(water spraying) - [eden] Cetaceans, you know, whales, dolphins, porpoises, are really canaries in the coal mine.

(water spraying) They tell us the health of our oceans.

And so when they're not doing that well, we really need to listen.

(wistful music) - [narrator] What had happened to the humpbacks?

And how did the scientific community mobilize to answer this question?

(dramatic music) - [announcer] Major funding for this program was provided by the Batchelor Foundation, encouraging people to preserve and protect America's underwater resources.

Additional funding was provided by the Parrot Family Endowment for Environmental Education.

(wistful music) - [narrator] For decades, scientists in southeast Alaska and the main Hawaiian Islands have been studying the humpback whales that frequent their waters.

(whale calling) - [andy] The whales are in Alaska They definitely start to drop off in November through December with a very low point in January, and then they start coming back up in abundance across the late winter and early spring.

(camera shutter clicking) (whimsical music) - [narrator] The vast majority of whales that feed in southeast Alaska will migrate thousands of miles to the main Hawaiian Islands to breed in late winter and early spring.

- [andy] I think we estimate now it's probably 88%.

What seems to drive the areas that the animals travel to, seems to be where they went with their moms.

(gentle music) If you were born in Hawai i and your mom brings you up to Alaska in your first year, you're gonna come back to Alaska and the odds are, you're gonna go back to Hawai i as well.

- [narrator] Experts in both locations are used to seeing many of the same whales year after year.

So when the animals stopped showing up in their usual numbers, people became concerned.

(regal music) - [eden] In 2018, the Hawaiian Islands Humpback Whale National Marine Sanctuary, helped to convene over 30 researchers and I think it was over 17 institutions, to come together and try to figure out what's going on with our North Pacific stock of humpback whales.

And so this involves people from all the different islands here in Hawai i and Alaska, and we're really trying to work together to figure out what is going on.

(water spraying) - [marc] It's very important, I think, to have these discussions and these collaborations, because we have a lot of knowledge gaps.

- [joe] The consensus of the meeting was that we needed to, you know, figure out, you know, what their status was now, using different methods.

(regal music) - (Sanctuary Employee) Sighting!

9-2-0-9-2-3.

- [narrator] Researchers at the Hawaiian Islands Humpback Whale National Marine Sanctuary came up with a three-pronged approach to determine how many whales are coming to the winter breeding grounds each season.

- [eden] The hope is that if we combine each one of these data that we'll get a better understanding of how many animals are really in our waters here in Maui.

(upbeat music) (air hissing) - [marc] We have a number of acoustic recorders out in various parts of the Hawaiian Islands.

- [narrator] While on the breeding grounds, the male humpbacks perform elaborate songs, which become the dominant source of sound underwater.

(whales calling) - [marc] The acoustic recorders help us determine when whales are in Hawaiian waters, because the acoustic energy increases, so we can measure the arrival of the whales in the December timeframe.

The acoustic levels go up rapidly.

They usually peak around February or March, and then decrease in the April timeframe.

(thoughtful music) Now, that allows us to track the whale season itself, but then we can also use that information to compare the whale seasons between years.

- [narrator] The scientists discovered that between 2015 and 2018 the acoustic energy recorded at six sites off Maui dropped by 50% during the peak whale season.

- [marc] Not only was the peak of the chorusing was lower during those three years, but we could tell that the season changed and the whales started to leave Hawaiian waters earlier and earlier.

(boat engine whirring) (majestic music) - [narrator] Knowing this, the experts decided to count the actual numbers of whales in the area.

Sanctuary staff began regular boat surveys in the leeward waters off west Maui.

This is an area where whales tend to occur in large numbers, and it overlaps with the coverage area of the acoustic recorders.

- [eden] We conduct roughly about 10 to 12 vessel in a whale season.

- [narrator] Surveys are scheduled between December and April of each year to capture the beginning, peak, and tail end of the humpback whale breeding season.

- [eden] Each survey is a full day and we follow a systematic transect line.

- [narrator] While the boat surveys are underway, (low urgent music) Ph.D.

Candidate Anke K gler counts whales from an elevated shore station overlooking the same area.

- [anke] So we try to schedule the boat and land days at the same time, and I'm also doing additional land surveys.

I come up here like once a week and I scan the entire area for any humpback whale presence from about eight o'clock to 2:30, and then I do scans for 30 minutes every hour and basically try to get the location of every whale I see.

- [narrator] Once Anke spots a whale, she uses a surveyor's instrument called a theodolite to measure the horizontal and vertical angle of its position.

- [anke] And we can use those angles the actual GPS position of the whale.

It gives us a spatial distribution of the whales at a given time in the area.

- [marc] By combining these efforts, is show that between 2015 and 2018, there was approximately a 50% decrease in the number of whales that were occupying the area that we've been monitoring.

- [narrator] In the three years that followed, the numbers of whales generally increased again, though scientists say there were some fluctuations in the lengths of the seasons.

- [anke] I've seen for example, like shifts in the peak of the season.

The numbers I'm seeing drop like earlier in some years.

- [rachel] No, I think there Yeah, there was, yeah.

So just head down towards that way.

- [rachel] Fine.

- Yeah.

- [narrator] Researchers with the Keiki Kohola Project, who focus on mothers and calves, also recorded a drastic decline in whale numbers over a three-year period.

(thoughtful music) - [rachel] Our long-term study is a transect-based study, which encompasses one of the main areas that's favored by mother and calf pairs when they're in Hawai i, and that's been underway since 2008 and we do it three times a season.

Mid-January, mid-February, and mid-March surveys.

2016 is when we first saw a really clear decline in the numbers of whales we were seeing in Hawaiian waters, and then over the next two years that played out.

When we compared 2013 and 14 to 2017 and 18, those two-year periods, we were seeing a 76% decrease in the numbers of mothers and calves that we encountered on those transect lines.

Related to that, we also started to see a change in seasonality.

2019 was when we first saw our numbers coming back up quite healthily in Hawai i and we were getting back to maybe where we were at the start of the demise.

(plane engine whirring) - [narrator] Another team of experts saw similar improvements when in 2019 and 2020, they conducted aerial surveys to estimate the whales' density.

(gentle music) (radio chattering) This group focused its efforts on the entire Maui Nui region, where humpbacks are known to aggregate in the relatively shallow water.

- [joe] The highest densities of humpbacks are here between those four islands.

- [adam] What we've been doing is three aerial surveys, one prior to the peak of the season, one at the peak, and one post peak.

(radio chattering) - [narrator] The scientists used the same survey methods as they did during aerial surveys conducted between 1993 and 2003 to ensure that results would be comparable.

At that time, they discovered that the whale population was increasing at an average rate of 7% per year.

The 2019 and 2020 surveys, which covered a smaller area, didn't show the same annual increase, but the findings suggest that the population of humpbacks that winter in Hawai i appears to be relatively stable.

- [joe] That's one of the most promising statistics that we picked up in 2019.

There's 9% of the pods that we saw had calves and that's higher than it had been in the past.

(thoughtful music) (radio beeping) - [narrator] Like all their colleagues in Hawai i, a network of research partners in southeast Alaska observed similar trends.

- [andy] We were finding far fewer animals in 2016, 2017, and than we had in previous years, we're seeing record low numbers of calves, and we're were finding a large number of skinny and emaciated whales.

- [john] By the time 2019 came around, things were looking a little bit better.

We started seeing calves again, the whales seemed a little bit healthier, looked fatter, and we saw numbers increase in the southeast.

In the Prince William Sound, the numbers have not quite bounced back yet, we're still seeing really low, low numbers.

- [martin] Glacier Bay National Park, they have this incredible data set dating back 30 plus years of the same individuals coming back with incredibly high consistent site fidelity.

And unfortunately, some of their main animals just vanished and they still have not come back there.

- [narrator] So what had happened to the whales during that three-year period?

- [adam] There seemed to be three different phenomenon that were converging at the same time.

One was a strong El Nino and that's a normal phenomenon that sometimes occurs, of course.

- [narrator] In addition, a shift occurred in the Pacific Decadal Oscillation, a longer-lived pattern of climate variability.

- [adam] Which is also a normal kind of warming event, but on a longer-term scale.

- [narrator] These two warming events coincided with the worst marine heatwave ever recorded in the North Pacific.

- [rachel] And that created a lens of warm water that became known as the blob, mainly because it crept very slowly and expanded across the waters of the North Pacific.

- [martin] Putting them all together, - [rachel] At that point, you had three levels of warming that were all going to amplify each other.

And once those waters are warm, the problem is that they don't turn over at the same rate, and so nutrients don't cycle through the water.

- [marc] Which then, of course, effect the life that depends on those nutrients.

- [john] It will change the composition of the plankton.

A lot more warm water species can show up.

They don't have as much fat in them, so that in turn means less fatty food for things like krill and herring, which makes it harder for those those animals to make it.

- [narrator] In essence, the food the whales depend on while in Alaska had been drastically reduced in the areas they're known to frequent.

- [john] They're feeding on krill, little shrimp-like creature that get really dense aggregations, and, small schooling fish.

So things like herring, capelin, sand lance, sometimes they eat juvenile salmon.

So it's, fish and krill is the main diet.

- [marc] The first year that we noticed these changes, there were an unusually high number of reports of dead whales, both here in Hawai i, but also in Alaska, but we didn't think that it was enough to explain the decrease in whale numbers.

- [martin] These whales follow food.

So if we're seeing less sightings of animals in areas that are really well-researched, there's a good chance that these whales have been moved elsewhere.

They could be utilizing offshore areas a little bit more.

There's certainly far less research effort out in these rough open waters.

- [marc] And during the breeding season, it could well be that a certain number of whales just didn't have enough fuel in their tank, so to speak, to make the migration to the breeding grounds, and so it would be a wasted effort.

- [narrator] Scientists say it's also possible that some of the whales migrated to one of the other known feeding grounds in the North Pacific, or possibly went to the northwestern Hawaiian Islands where there is no monitoring.

- [martin] As the climate changes, a that these sorts of events are becoming more frequent, and if this was a reaction to this sort of event, now what happens when this becomes the norm?

- [adam] I think that this really or the tip of the iceberg.

- [narrator] Knowing the impact the severe marine heatwave had on the whales made scientists want to learn more about the animals' health and body condition, and how that changes over the course of a year as well as between years.

- [martin] Unfortunately, we still what a healthy humpback whale looks like.

So for us to be able to figure out when a population is impacted, we need to know what the baseline is.

(water spraying) (low urgent music) - [narrator] To do so, scientists from the Marine Mammal Research Program at the University of Hawai i at Manoa are collaborating closely with other experts in Hawai i and Alaska.

Ph.D. student Martin van Aswegen spends each April through October in southeast Alaska conducting research with the Alaska Whale Foundation.

- [andy] We're studying the distribution of the animals, the abundance of the animals, looking at the numbers of calves they're producing, and how that changes across the season.

(drone whirring) - [martin] Three, two, one.

- [narrator] In addition, Martin is collecting regular measurements of the animals from the air.

- [martin] We're using these drones to noninvasively get over the top of the whales as they're surfacing.

And as they surface, we can get a video, a high-resolution image of their body contours so we can see how long the whale is, but also how wide the animal is, and using some software that we have, we can measure the total length of the animal, as well as the width, across 20 different points on the body.

We can do this again and again and again, with the same animals and different animals, and this allows us to see how quickly these whales are gaining mass.

Their job up here is essentially just to gain as much mass and weight as they can in preparation for when they start to migrate south when they're fasting.

- [lars] So we're trying to estimate how much they need to feed up in their foraging grounds, so Alaska, and what is the cost of the migration down here to Hawai i?

- [martin] In addition to our we're sampling in Hawaii as well.

We're sampling January, February, March.

Some of the measurements that we're getting are quite surprising, things like adults losing up to 28 inches of their body width while on the breeding grounds, for example, and that's without a calf, that's just a regular mature adult.

- [narrator] Between 2018 and 2021, Martin captured approximately 4,100 measurements of over 3,200 humpbacks in Hawai i and Alaska.

This includes repeat sightings of more than 80 individual animals in both locations within six months of each other.

- [andy] The way you recognize an individual whale is by looking at the underside of its tail, its fluke.

Every whale has unique black and white pigmentation patterns and the shape of the trailing edge of the fluke.

(low urgent music) - [narrator] Whale experts from all over have long used photographs of the flukes as a way to identify the individual animals they're studying.

New technology has revolutionized this - [lars] Very recently, a research group has started an initiative called Happy Whale, which is a software that allows automatic detection and matching of fluke shots, which is very time-consuming with with the naked eye.

- [narrator] Now whale researchers everywhere can not only upload their images for faster identification within their database, but they're also able to see if any of their colleagues have seen the same whale elsewhere.

(water splashing) - [lars] This new Happy Whale initiative is really helpful for all of us as a research community to try to understand the movement patterns (water spraying) (gentle music) - [narrator] In addition, the scientists collect small tissue biopsies of some of the whales they measure.

This allows them to study the animals' diet, look at their fat stores, and determine if females are pregnant.

- [lars] The biopsy samples also tell us about different stress levels in these animals as well.

- [adam] As a whale is fasting and losing its body mass, it should be increasing in its stress levels.

This part was.

What we're interested in is kind of measuring a baseline for that, so that when climate events occur, we have something to compare it with.

(regal music) - [martin] Coming up.

Take off.

(drone whirring) One o'clock.

- [narrator] Whale experts in Alaska and Hawai i are relieved to see that the humpbacks seem to be recovering from the impacts of the recent marine heatwave.

But, they say, they are also keenly aware that they need to be prepared for the future.

- [andy] People who study these warm water events predict that they're gonna happen more frequently and they're gonna be more persistent and last for longer moving forward as a result of climate change, and so that gives us a lot of concern that what we saw in those years, 2016 to 2018, will almost certainly happen again.

- [adam] It makes us aware of being and how we need to really use these different tools that we're using right now to continue to monitor the population.

And collectively being able to monitor not just the whales, but the environmental factors as well is going to be critical.

(regal music) (whale calling) (inspiring music) (water rushing) (drone whirring) (water spraying) - [announcer] Major funding for this program was provided by The Batchelor Foundation, encouraging people to preserve and protect America's underwater resources.

Additional funding was provided by the Parrot Family Endowment for Environmental Education.

(upbeat music)