Humpback whales are making a comeback – here’s one reason why

University of Southern Denmark

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Humpback in the Senyavin Strait in far eastern Russia.

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Credit: Olga Filatova/University of Southern Denmark

When University of Southern Denmark whale researcher Olga Filatova set off on her first field trip in 2000, she spent five years looking for whales before she saw a humpback.

“It was incredibly rare to spot one back then. Today, we see them almost every day when we’re in the field,” she says. “We don’t know exactly how many humpbacks there are now, but definitely many more than when I started.”

A cautious estimate from the Endangered Species Coalition puts today’s population at around 80,000—up from just 10,000 at their lowest point. That makes humpbacks one of the great success stories of conservation.

One major reason is that commercial whaling was banned in 1986. But according to Olga Filatova, their willingness to switch between different food sources also matters.

“Unlike several other whale species, humpback whales prefer to stay in an area, even if one food source runs out – as long as there is something else to eat. We’ve seen humpback whales hunt cod in an area, and when the cod disappeared, they switched to krill,” says Olga Filatova.

She and colleagues observed this between 2017 and 2021 during summers and autumns in the Senyavin Strait east of the Chukotka Peninsula in far eastern Russia, north of the Bering Sea. In 2017, they saw a group of about 100 humpback whales hunting polar cod. The following year, there was no cod, but the whales had stayed in the area and switched to hunting krill. 

“This showed us that whales can change hunting behavior and food preference when conditions change. That’s a high degree of flexibility and likely one of the reasons for their evolutionary success,” explains Olga Filatova.

Other species of fin whales tend to burn more energy searching for their favorite foods and are more likely to leave an area when prey vanishes. Humpbacks, however, are not built for speed. In fact, they have a reputation for being the laziest hunters of all whales. They invent many methods to trick prey and capture it with as low energy expenditure as possible.

For example, one of their techniques called “trap feeding” involve simply floating on the surface with their mouths open in areas where sea gulls are catching fish. As the fish try to escape the gulls, they swim straight into the whale’s mouth, thinking that it is a good safe shelter.

Moving into new habitats

“They’re not fast, and they’ve got these big, clumsy flippers—but what they lack in speed, they make up for in creativity and willingness to eat whatever’s available,” Filatova says.

Filatova is optimistic about humpbacks’ future. Not only are they resourceful eaters with relatively low energy demands, but they’re also one of the few species actually benefiting from climate change. As sea ice melts, new habitats open up—and they’re already moving in.

“We are getting more and more reports of humpbacks in Arctic waters where they have never been seen before,” she says.

Humpback whales migrate yearly from tropical to polar seas, spending winter in warm waters and feeding in rich cold waters of high latitudes in summer.

“I’m not worried about them. I’m more worried about whales that can only live in Arctic waters – that’s the bowhead whale, the beluga whale, and the narwhal,” says Olga Filatova.

The study behind this article was published in the journal Marine Mammal Science. The field trips between 2017 and 2021 were supported by the Russian Science Foundation. You can read the study here.

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How to know what humpbacks eat:

You might spot a humpback whale snatching a fish from the water’s surface if you’re lucky enough to be out on a boat. But most of their hunting takes place out of sight, below the surface. To figure out what they’re eating, researchers need different tools—and in this study, one of those tools was stable isotope analysis of whale skin samples. By analyzing nitrogen stable isotope in whale skin, scientists can tell what the whales had been eating. Lower values of 15N stable isotope indicate a diet rich in krill, while higher ratio of this isotope point to fish like cod. That’s because animals higher up the food chain tend to accumulate heavier nitrogen isotopes.

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Humpback whales are 11–19 meters long (females are the largest), weigh up to 35 tons, and can live 50–60 years. A female carries her calf for about 11.5 months and gives birth every two to three years. Humpbacks are found in oceans all over the world and travel up to 25,000 km each year.

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Olga Filatova is a postdo and research leader at the Department of Biology and the SDU Climate Cluster at University of Southern Denmark. Supporters of her research include Aaage V. Jensens Naturfonde. 

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Journal

Marine Mammal Science

DOI

10.1111/mms.70071 

Method of Research

Observational study

Subject of Research

Animals

Article Title

Changing the Menu: Humpback Whale (Megaptera novaeangliae) Diet Switching in Senyavin Strait, Chukotka

Humpbacks in the Senyavin Strait in far eastern Russia

Humpback in the Senyavin Strait in far eastern Russia.

Humpback in the Senyavin Strait in far eastern Russia.

Credit

Olga Filatova/University of Southern Denmark

 

Team investigates significance of newly discovered hydrothermal fields off the island of Milos

MARUM - Center for Marine Environmental Sciences, University of Bremen

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Sampling fluids of 180 degree Celsius at the White Sealhound structure. Photo: MARUM – Center for Marine Environmental Sciences, University of Bremen

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Credit: MARUM – Center for Marine Environmental Sciences, University of Bremen

The study identifies three major vent areas — Aghia Kiriaki, Paleochori–Thiorychia, and Vani — all located along active fault zones that run across the Milos shelf. These faults belong to a large tectonic depression, the Milos Gulf–Fyriplaka graben, which has lowered the seafloor to depths of up to 230 meters. The close alignment of vents with these geological structures shows that tectonic activity plays a key role in determining where hydrothermal venting occurs.

“We never expected to find such a large field of gas flares off Milos,” says Solveig I. Bühring, senior author of the study and scientist at the MARUM – Center for Marine Environmental Sciences, University of Bremen, who led the expedition M192 during which the vents were discovered. “When we first observed the vents through the ROV cameras, we were stunned by their diversity and beauty — from shimmering, boiling fluids to thick microbial mats covering the chimneys.”

According to first author Paraskevi Nomikou of the National and Kapodistrian University of Athens, the spatial pattern of these vent clusters is closely controlled by the island’s tectonic fabric:

“Our data clearly show that the gas flares follow the patterns of the major fault systems around Milos,” Nomikou explains. “Different fault zones influence different vent clusters, especially where several faults meet. These tectonic structures strongly control how and where hydrothermal fluids reach the seafloor.”

The findings demonstrate how active faulting and ongoing geological processes have shaped the evolution of these vent fields. This discovery establishes Milos as one of the most significant natural laboratories in the Mediterranean for studying the interplay between tectonics, volcanism, and hydrothermal activity.

The results are also relevant for the MARUM-based Cluster of Excellence “The Ocean Floor – Earth's Uncharted Interface.” A follow-up expedition to Milos, the Kolumbo submarine volcano off Santorini, and Nisyros is planned. The research is the result of close collaboration between Greek and German institutions, including the National and Kapodistrian University of Athens, MARUM – University of Bremen, Friedrich-Alexander-Universität Erlangen-Nürnberg, ICBM – Institute for Chemistry and Biology of the Marine Environment Oldenburg, and Constructor University Bremen.

Original publication:

Paraskevi Nomikou, Konstantina Bejelou, Andrea Koschinsky, Christian dos Santos Ferreira, Dimitrios Papanikolaou, Danai Lampridou, Stephanos P. Kilias, Eirini Anagnostou, Marcus Elvert, Clemens Röttgen, Joely M. Maak, Alissa Bach, Wolfgang Bach, Areti Belka, Evgenia Bazhenova, Karsten Haase, Charlotte Kleint, Effrosyni Varotsou, Palash Kumawat, Erika Kurahashi, Jianlin Liao, Eva-Maria Meckel, Ignacio Pedre, Wiebke Lehmann, Enno Schefuß, Michael Seidel, Sotiria Kothri & Solveig I. Bühring: Structural control and depth clustering of extensive hydrothermal venting on the shelf of Milos Island. Scientific Reports volume 15 (2025). DOI: https://doi.org/10.1038/s41598-025-26398-y

Contact:

Dr. Solveig I. Bühring
Petrology of the Ocean Crust
MARUM – Center for Maine Environmental Sciences, University of Bremen
Email: sbuehring@marum.de

 

Participating institutions:

• Department of Geology and Geoenvironment, National and Kapodistrian University of Athens (Greece)
• School of Science, Physics & Earth Sciences, Constructor University Bremen, Germany
• Faculty of Geosciences, University of Bremen
• MARUM – Center for Marine Environmental Sciences, University of Bremen
• GeoZentrum Nordbayern, Friedrich-Alexander-University Erlangen-Nuernberg
• ICBM – Institute for Chemistry and Biology of the Marine Environment, Carl Von Ossietzky University of Oldenburg

 

MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations. It publishes its quality-assured scientific data to make it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperation with companies and industrial partners is carried out in accordance with its goal of protecting the marine environment.

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Journal

Scientific Reports

DOI

10.1038/s41598-025-26398-y 

Article Title

Structural control and depth clustering of extensive hydrothermal venting on the shelf of Milos Island

 

The mystery of the missing deep ocean carbon fixers

UCSB study reshapes understanding of deep-ocean carbon storage with implications for long-term climate stability

University of California - Santa Barbara

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(Santa Barbara, Calif.) — In a step toward better understanding how the ocean sequesters carbon, new findings from UC Santa Barbara researchers and collaborators challenge the current view of how carbon dioxide is “fixed” in the sunless ocean depths. UCSB microbial oceanographer Alyson Santoro and colleagues, publishing in the journal Nature Geoscience, present results that help to reconcile discrepancies in accounting for nitrogen supply and dissolved inorganic carbon (DIC) fixation at depth.

“Something that we’ve been trying to get a better handle on is how much of the carbon in the ocean is getting fixed,” Santoro said. “The numbers work out now, which is great.”  

This project was supported in part by the National Science Foundation.

Who’s doing the fixing?
The ocean is the Earth’s largest carbon sink, buffering us from the worst that climate change can throw at us by absorbing a third of our carbon dioxide emissions, which in turn regulates global temperatures. We rely heavily on the ocean for this phenomenon, which is why it’s important to  fully understand the complex processes that enable it.

“We want to know how carbon moves around the deep ocean, because in order for the ocean to impact the climate, carbon has to make it from the atmosphere to the deep ocean,” Santoro said.

In the ocean, the majority of this inorganic carbon fixing work is conducted by microbes. Phytoplankton, a group of single-celled organisms that take up inorganic carbon dioxide (including dissolved carbon dioxide gas) at the ocean’s surface, are known as autotrophs. They produce their own food in the same way plants on land photosynthesize carbon dioxide and water, producing organic matter (sugars) and oxygen.

The prevailing idea has been that while most DIC fixation happens in the upper, sunlit layer thanks to photosynthetic phytoplankton, a significant amount of non-photosynthetic DIC fixation also occurs in the “dark” layers of the ocean, an assimilation dominated mainly by autotrophic archaea that evolved to oxidize ammonia (a nitrogen-containing compound) for energy rather than sunlight.

However, when tracking these carbon fixing microbes’ nitrogen energy budget through water column sampling, researchers soon found that the numbers weren’t matching up.

“There was a discrepancy between what people would measure when they went out on a ship to measure carbon fixation and what was understood to be the energy sources for microbes,” Santoro said. “We basically couldn’t get the budget to work out for the organisms that are fixing carbon.” They needed energy to do that, she explained, but there didn’t seem to be enough available nitrogen-based energy to go around in the deep ocean for the rates of carbon fixation being reported throughout the water column.

This mystery has long been on the minds of Santoro and the paper’s lead author Barbara Bayer, who have been working to fill this gap in our understanding of the ocean’s carbon cycle for almost a decade. Previous work has explored the hypothesis that maybe these carbon-fixing archaea were more efficient at their jobs than assumed, requiring less nitrogen to fix carbon, though their results indicated that was not the case.

For this paper, the team took a different approach, asking instead how big the contribution of these ammonia oxidizers was to the total dissolved inorganic carbon fixation rates in the dark ocean. To find out, Bayer devised a clever experiment.

“She came up with a way to specifically inhibit their activity in the deep ocean,” Santoro explained. By restricting the oxidizers with a special chemical, she continued, the rate of carbon fixing should be drastically reduced. The inhibitor, phenylacetylene, was confirmed to have no other measurable effects on other community processes.

Their results indicated that despite inhibiting these ammonia oxidizers — mostly archaea that are abundant in the dark ocean — the rate of carbon fixation in the study areas didn’t drop as much as expected.

So if not the ammonia-oxidizing archaea, then who could be doing the carbon fixing in the depths? The list of suspects has grown to include other microbes in the neighborhood, particularly bacteria and some archaea.

“We think that what this means is that the heterotrophs — microorganisms that feed on organic carbon from decomposing microbes and other marine life — are taking up a lot of inorganic carbon in addition to the organic carbon that they usually consume,” Santoro said, “meaning that they’re also responsible for fixing some carbon dioxide.

“And that’s really interesting because even though we know this to be a theoretical possibility, we didn’t really have a quantitative number on what fraction of the carbon in the deep ocean was getting fixed by these heterotrophs versus autotrophs. And now we do.”

These findings also help to paint a clearer picture of how the deep ocean’s food web works.

“There are basic aspects of how the food web works in the deep ocean that we don’t understand,” Santoro said, “and I think of this as figuring out how the very base of the food web in the deep ocean works.”

More mysteries of the deep

Further work in this realm for Santoro and her collaborators will dive into the finer aspects of carbon fixation in the ocean, such as how the nitrogen cycle and carbon cycle interact with other elemental cycles in the ocean, including for iron and copper.

“The other thing we’re trying to figure out is once these organisms fix the carbon into their cells, how does it become available to the rest of the food web?” she noted. “What kinds of organic compounds might they be leaking out of their cells that could be feeding the rest of the food web with?”

Research in this paper was also conducted by Nicola L. Paul, Justine B. Albers and Craig A. Carlson at UCSB; Katharina Kitzinger and Michael Wagner at the University of Vienna as well as Mak A. Saito at Woods Hole Oceanographic Institution.

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Journal

Nature Geoscience

Article Title

Minor contribution of ammonia oxidizers to inorganic carbon fixation in the ocean