Long-distance relationship revealed in the seemingly random behavior of bowhead whales

Applying chaos theory to the movement of iconic arctic whales uncovered a 24-hour diving cycle and a long-range (~100 km) synchronization.

Bowhead whales are among the largest and longest-lived mammals in the world.

They play a vital role in the marine ecosystems of the Arctic Ocean, yet relatively little is known about their foraging and diving behaviors.

Now, in a paper to be published in the journal Physical Review Research, a team of scientists from Japan, Greenland and Denmark have detected patterns in the whales' behavior that could offer clues into how they forage and socialize.

Associate Professor Evgeny A. Podolskiy at the Arctic Research Center, Hokkaido University, Professor Jonas Teilmann at the Department of Ecoscience, Aarhus University, and Professor Mads Peter Heide-Jørgensen at the Department of Birds and Mammals, Greenland Institute of Natural Resources, studied 144 days of diving records of 12 bowhead whales tagged in Disko Bay, West Greenland.

Because whale diving behavior can be seen as a chaotic, self-sustained oscillation that balances the need for food at depths with the need for oxygen at the surface, the researchers used a dynamical systems chaos approach to uncover patterns within the apparently disorderly collective behavior.

Their analysis detected a 24-hour cycle of diving during the spring, with the whales swimming deepest in the afternoon to track the daily movement of their prey towards the surface, a phenomenon known as the diel vertical migration.

"We find that foraging whales dive deeper during the daytime in spring, with this diving behavior being in apparent synchrony with their vertically migrating prey," said Heide-Jørgensen.

"Until now, this hasn't been shown for spring, and remained contradictory for autumn."

The research team also made the surprising discovery of two bowhead whales diving in synchrony over the course of a week at a time, even when they were around one hundred kilometers apart.

The pair -- one female and one of unknown sex -- were sometimes as close as five kilometers and sometimes hundreds of kilometers apart, yet they would closely time their diving bouts for durations of up to a week, although to different depths.

The synchronization was observed when they were within acoustic range of each other, which can exceed 100 kilometers, although the researchers didn't record the whales' sounds to determine whether they were interacting, as it remains a technically challenging task.

"Without direct observations, such as recordings of the two whales, it isn't possible to determine that the individuals were exchanging calls," said Teilmann, nevertheless, "the observed subsurface behavior might be the first evidence supporting the acoustic herd theory of long-range signaling in baleen whales proposed by Payne and Webb back in 1971."

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Toothed whale echolocation organs evolved from jaw muscles

Genetic analysis finds evidence suggesting that acoustic fat bodies in the heads of toothed whales were once the muscles and bone marrow of the jaw.

Dolphins and whales use sound to communicate, navigate and hunt.

New research suggests that the collections of fatty tissue that enable toothed whales to do so may have evolved from their skull muscles and bone marrow.

Scientists at Hokkaido University determined DNA sequences of genes which were expressed in acoustic fat bodies -- collections of fat around the head that toothed whales use for echolocation.

They measured gene expression in the harbor porpoise (Phocoena phocoena) and Pacific white-sided dolphin (Lagenorhynchus obliquidens). Their findings were published in the journal Gene.

The evolution of acoustic fat bodies in the head -- the melon in the whale forehead, extramandibular fat bodies (EMFB) alongside the jawbone, and intramandibular fat bodies (IMFB) within the jawbone -- was essential for sound use such as echolocation.

However, little is known about the genetic origins of those fatty tissues.

"Toothed whales have undergone significant degenerations and adaptations to their aquatic lifestyle," said Hayate Takeuchi, a PhD student at Hokkaido University's Hayakawa Lab and first author of the study.

One adaptation was the partial loss of their sense of smell and taste, along with the gain of echolocation to enable them to navigate in the underwater environment.

The researchers found that genes which are normally associated with muscle function and development were active in the melon and EMFBs.

There was also evidence of an evolutionary connection between the extramandibular fat and the masseter muscle, which in humans connects the lower jawbone to the cheekbones and is a key muscle involved in chewing.

"This study has revealed that the evolutionary tradeoff of masticatory muscles for the EMFB -- between auditory and feeding ecology -- was crucial in the aquatic adaptation of toothed whales," said Assistant Professor Takashi Hayakawa of the Faculty of Environmental Earth Science, who led the study.

"It was part of the evolutionary shift away from chewing to simply swallowing food, which meant the chewing muscles were no longer needed."

Analysis of gene expression in the intramandibular fat detected activity of genes related to immune functions, such as the activation of some elements of the immune response and regulation of T cell formation.

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Menopause explains why some female whales live so long

Females of some whale species have evolved to live drastically longer lives so they can care for their families, new research shows.

The study focussed on five whale species that -- along with humans -- are the only mammals known to go through menopause.

The findings show that females of these whale species that experience menopause live around 40 years longer than other female whales of a similar size.

By living longer without extending their "reproductive lifespan" (the years in which they breed), these females have more years to help their children and grandchildren, without increasing the "overlap" period when they compete with their daughters by breeding and raising calves at the same time.

This new research shows that -- despite being separated by 90 million years of evolution -- whales and humans show remarkably similar life histories, which have evolved independently.

The study was carried out by the universities of Exeter and York, and the Center for Whale Research.

"The process of evolution favours traits and behaviours by which an animal passes its genes to future generations," said lead author Dr Sam Ellis, from the University of Exeter.

"The most obvious way for a female to do this is to breed for the entire lifespan -- and this is what happens in almost all animal species. There are more than 5,000 mammal species, and only six are known to go through menopause.

"So the question is: how and why did menopause evolve? Our study provides some of the answers to this fascinating puzzle."

Menopause is known to exist in five species of toothed whale: short-finned pilot whales, false killer whales, killer whales, narwhals and beluga whales.

As well as outliving females of other similar-sized species, females in these five species outlive the males of their own species. For example, female killer whales can live into their 80s, while males are typically dead by 40.

"The evolution of menopause and a long post-reproductive life could only happen in very specific circumstances," said Professor Darren Croft, of the University of Exeter and Executive Director at the Center for Whale Research

"Firstly, a species must have a social structure in which females spend their lives in close contact with their offspring and grand-offspring.

"Secondly, the females must have an opportunity to help in ways that improve the survival chances of their family. For example, female toothed whales are known to share food and use their knowledge to guide the group to find food when it is in short supply."

Professor Dan Franks, from the University of York, said: "Previous research on menopause evolution has tended to focus on single species, typically humans or killer whales.

"This study is the first to cross several species, enabled by the recent discovery of menopause in multiple species of toothed whales.

"Our study provides evidence that menopause evolved by expanding female lifespan beyond their reproductive years, rather than from reduced reproductive lifespan.

"This is a question that has long been asked in anthropology, but can only be directly answered with a comparative study."

Commenting on parallels with the evolution of menopause in humans, Professor Croft added: "It's fascinating that we share this life history with a taxonomic group we're so different from.

"Despite these differences, our results show that humans and toothed whales show convergent life history -- just like in humans, menopause in toothed whales evolved by selection to increase the total lifespan without also extending their reproductive lifespan."

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Slimming down a colossal fossil whale

A 30 million year-old fossil whale may not be the heaviest animal of all time after all, according to a new analysis by paleontologists at UC Davis and the Smithsonian Institution. The new analysis puts Perucetus colossus back in the same weight range as modern whales and smaller than the largest blue whales ever recorded. The work is published Feb. 29 in PeerJ.

A fossil skeleton of Perucetus was discovered in Peru and described in a paper in Nature last year.

The animal lived about 39 million years ago and belonged to an extinct group of early whales called the basilosaurids.

Perucetus' bones are unusually dense. Mammal bones usually have a solid exterior and are spongy or hollow in the center.

Some animals have more of the center filled in with solid bone, making them dense and heavy.

In aquatic animals, heavy bones can offset buoyancy from body fat and blubber, allowing the animal to maintain neutral buoyancy in water or -- in the case of the hippopotamus -- to walk on river beds.

The fossil whale bones have both extensive in-filling and extra growth of bone on the outside as well, a condition called pachyostosis also seen in some modern aquatic mammals, such as manatees.

Based on a series of assumptions, the original authors (Giovanni Bianucci at the University of Pisa, Italy and colleagues) estimated a body mass for Perucetus of 180 metric tons (ranging from 85 to 340 metric tons). This would make Perucetus as heavy as, or heavier than the biggest blue whales known, even though it is considerably shorter at 17 meters long compared to a blue whale at about 30 meters.

How to weigh a whale?

Professor Ryosuke Motani, a paleobiologist at the UC Davis Department of Earth and Planetary Sciences, said that these estimates would make Perucetus impossibly dense.

"It would have been a job for the whale to stay at the surface, or even to leave the sea bottom -- it would have required continuous swimming against the gravity to do anything in the water," Motani said.

Motani and Nick Pyenson at the Smithsonian Institute National Museum of Natural History reexamined the assumptions used to make those estimates.

The first problem is that Bianucci et al used the fossil bones to estimate the weight of the skeleton, then extrapolated to the weight of the entire animal, assuming that the skeletal and non-skeletal mass would scale at the same rate with increasing body size.

But measurements of other animals show this is not the case, Motani and Pyenson argue.

The original estimates also overestimated how much overall body mass increases as a result of pachyostosis.

But evidence from manatees shows that their bodies are relatively light relative to their skeletal mass.

Motani and Pyenson estimate that the 17-meter long Perucetus weighed in at 60 to 70 tons, considerably less than the known weights of blue whales.

A Perucetus that grew to 20 meters could weigh over 110 tons, still well short of the largest blue whales at 270 tons.

"The new weight allows the whale to come to the surface and stay there while breathing and recovering from a dive, like most whales do," Motani said.

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Baleen whales evolved a unique larynx to communicate but cannot escape human noise

Baleen whales are the largest animals to have ever roamed our planet and as top predators play a vital role in marine ecosystems. To communicate across vast distances and find each other, baleen whales depend critically on the production of sounds that travels far in murky and dark oceans.

However, since whale songs were first discovered more than 50 years ago, it remained unknown how baleen whales produce their complex vocalizations -- until now.

A new study in the journal Nature reports that baleen whales evolved unique structures in their larynx that enable their low-frequency vocalizations, but also limit their communication range.

The study was led by voice scientists Professor Coen Elemans, at the Department of Biology, University of Southern Denmark and Professor Tecumseh Fitch at the Department of Behavioral and Cognitive Biology, University of Vienna in Austria.

"The toothed and baleen whales evolved from land mammals that had a larynx serving two functions: protecting the airways and sound production. However, their transition to aquatic life placed new and strict demands on the larynx to prevent choking underwater," says Tecumseh Fitch.

The study shows that baleen whales nevertheless can still produce sound with their larynx, but they have evolved novel structures to do so, that only exists in baleen whales. First, the tiny cartilages in the human larynx -- called the arytenoids -- that change the position of our vocal folds, have changed dramatically in whales.

"The arytenoids changed into large, long cylinders fused at the base to form a large U-shaped rigid structure that extends nearly the full length of the larynx," Elemans says.

"This is probably to keep a rigid open airway when they have to move huge amounts of air in and out during explosive surface breathing," states Fitch.

"We found that this U-shaped structure pushes against a big fatty cushion on the inside of the larynx. When the whales push air from their lungs past this cushion, it starts to vibrate and this generates very low frequency underwater sounds," says Elemans.

Trying to work on the biology and particularly physiology of whales is very challenging.

"Even though humans hunted whales close to the brink of extinction, they made very little effort in trying to learn about their physiology," says Magnus Wahlberg, whale expert at University of Southern Denmark and co-author on the study.

"Strandings are unique and rare opportunities to learn about these amazing animals, but even then, it is very hard to study physiology, because the tissue decays so fast. Whales are known to explode on the beach," adds Wahlberg.

Thanks to Danish and Scottish Marine Mammal Stranding Networks, the researchers could quickly extract the larynx of a sei, minke and humpback whale for close investigation in the lab.

"Our experiments showed for the first time how the whales make their very low frequency vocalizations," says Elemans.

To understand how muscle activity could change the calls, the researchers built a computational model of the entire whale larynx.

"Our model includes accurate 3D shapes of the larynx and its muscles, which made it possible to simulate, for example, how the frequency is controlled through muscle modulation," say Qian Xue and Xudong Zheng, professors at the Mechanical Engineering Department at Rochester Institute of Technology, USA, co-authors on the study.

"Our model accurately predicted the results of our experiments, but we could also calculate acoustic features we could not measure in the lab, such as the frequency range," says Weili Jiang, postdoc at Rochester Institute of Technology, USA, co-author on the study.

The models predicted the natural vocalizations of the whales very well.

However, these newly discovered anatomical features that allowed whales to successfully communicate in the vast oceans also poses unsurmountable physiological limits for many baleen whales.

Combining experiments and models, the researchers provide the first evidence that baleen whales are physiologically incapable of escaping anthropogenic noise, because it masks their voices, and thus limits their communication range.

"Regrettably, the frequency range and maximum communication depth of 100 meters we predict, overlaps completely with the dominant frequency range and depth of human-made noise caused by shipping traffic," Elemans says.

"The first acoustic recordings of humpback whale song by Roger and Katy Payne in 1970 resonated with humanity profoundly, started the flourishing field of marine bioacoustics, and sparked global interest in marine conservation efforts." says Coen Elemans.

"These recordings were so politically important then that they are aboard the Voyager space missions," he continues.

The Payne's made people aware how quiet the seas were before humans started the widespread use of propeller ships and continuously running shipboard generators. Those were the seas whales evolved in.

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Surprising behavior in one of the least studied mammals in the world

Some animals live in such remote and inaccessible regions of the globe that it is nearly impossible to study them in their natural habitats. Beaked whales, of which 24 species have been found so far, are among them: They live far from land and in deep oceanic waters, where they search for food at depths of 500 meters and more.

The record holder for the deepest dive by a mammal is a Cuvier's beaked whale, which in 2014 was measured to dive at least 2992 meters. A beaked whale also holds the mammalian record for the longest dive; 222 minutes.

Now, the world gets a new and surprising insight into the world of distant beaked whales through a scientific study of a population of Baird's beaked whales. The population has unexpectedly been found near the coast and in shallower waters than previously observed.

The study is led by whale biologists Olga Filatova and Ivan Fedutin from the University of Southern Denmark/Fjord&Bælt, and it is published in the journal Animal Behaviour.

Filatova and Fedutin have many years of whale studies in the northern Pacific behind them, and it was during an expedition to the Commander Islands in 2008 that they first saw a group of Baird's beaked whales near the coast.

"We were there to look for killer whales and humpback whales, so we just noted that we had seen a group of Baird's beaked whales and didn't do much about it. But we also saw them in the following years, and after five years, we suspected that it was a stable community frequently visiting the same area. We saw them every year until 2020, when Covid 19 prevented us from going back to the Commander Islands," explains Olga Filatova, a whale expert and postdoc at Department of Biology and SDU Climate Cluster, University of Southern Denmark.

The studied population of Baird's beaked whales came close to the coast -- within four km from land, and they were observed in shallow water; less than 300 meters.

"It is uncharacteristic for this species," says Olga Filatova, who also points out that the population likely has adapted to this particular habitat and thus deviates from the established perception that all beaked whales roam far out at sea and in deep waters.

"It means that you cannot expect all individuals within a specific species to behave the same way. This makes it difficult to plan species protection -- in this case, for example, you cannot plan based on the assumption that beaked whales only live far out in deep sea. We have shown that they can also live in shallow and coastal waters. There may be other different habitats that we are not aware of yet," says Olga Filatova.

There are many examples of individuals from the same whale species not behaving the same. In the whale world, it is common to find groups of the same species living in different places, eating different prey, communicating differently, and not liking to mingle with fellow species in other groups.

Some killer whale groups only hunt marine mammals like seals and porpoises, others only herring. Some humpback whales migrate between the tropics and the Arctic, others are residents in certain areas. Some sperm whale groups develop their own dialects for internal communication and do not like to communicate with others outside the group.

According to Olga Filatova, social learning is at play when groups develop preferences for, for example, habitats and prey.

There are many forms of social learning in the animal world. Imitation is the most complex form; the animal sees what others do and understands the motivation and reasoning behind it. Then there is "local enhancement," where an animal sees another animal heading to a specific place, follows, and learns that the place has value. This has been observed in many animals, including fish.

Olga Filatova believes that the population of Baird's beaked whales at the Commander Islands learns through "local enhancement": They see that some peers go to the shallow water near the coast, follow, and discover that it is a good place, probably because there are many fish.

"It becomes a cultural tradition, and it is the first time a cultural tradition has been observed among beaked whales," she says.

Other examples of cultural traditions in whales include when they develop specific hunting traditions: some slap their tails to stun fish, some generate waves to wash seals off ice floes, some chase fish onto the beach.

The researchers observed a total of 186 individuals of the Baird's beaked whale species at the Commander Islands from 2008-2019. 107 were only observed once and thus assessed to be transient whales. 79 individuals were spotted for more than one year and were thus assessed to be residents.

61 of the transient whales were seen interacting with the residents, and seven of them were seen in shallow water.

"The transients are not as familiar with local conditions as the residents, and therefore, they usually seek food at the depths that are normal for their species. But we actually observed some transients in the shallow area. These were individuals who had some form of social contact with the residents. It must be in that contact that they learned about the shallow water and its advantages," says Olga Filatova.

It is unclear how many Baird's beaked whales exist in the world.

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Global warming puts whales in the Southern Ocean on a diet

In the month of June, when winter bites in the southern hemisphere and the sea around the Antarctic freezes over, right whales swim north. Many of them gather in the bay outside the town of Hermanus in South Africa.

Here, the warmer South African water is perfect for mating or raising newborn calves. However, there is no food for the whales, and all winter long the right whale mothers use up their fat reserves to produce milk for their calves.

It is therefore extremely important that the whales eat a lot and fatten up in the cold waters around the Antarctic throughout the summer. But it seems there is not enough food. The whales arriving at the coasts of South Africa are thinner than they used to be.

This is the result of new research from Aarhus University. Since the researchers started to measure right whales in the 1980s, the whales have become increasingly thinner. This is explained by Fredrik Christiansen, a senior researcher at the Department of Ecoscience at Aarhus University, who is behind the new results.

"Right whales are 25 per cent thinner than they were in the 1980s. This is bad for the whale population, because it means that the newborn whale calves have a higher risk of dying. Fortunately, the right whales in the Southern Ocean are not endangered, but if this continues, they could become so," he says.

When the ice melts, food disappears

When winter comes, and the cows leave the Antarctic and swim north, they have to cope for several months without food. Several months in which they eat into the fat reserves they have built up through the warm and light summer season.

Throughout the summer, right whales swim around beneath the sea ice, open their mouths to take in seawater, krill and water fleas. The baleen inside their mouth is a sort of a giant filter and it filters the small animals from the salt water. This allows the whales to eat huge amounts of food without using a lot of energy.

But the large shoals of krill are shrinking -- and this means that the whales can't fatten up before winter as they used to," explains Fredrik Christiansen.

"The shoals of krill live on phytoplankton, which thrive best in the cold waters around the Antarctic. Here -- like plants on land -- they transform sunlight into energy. Rising sea temperatures mean there is less phytoplankton, fewer krill and thus less food for the whales.

Instead, the whales forage for food further north, where there is another and less energy-rich form of krill.

"Further north, there's less food for these small crustaceans. Therefore, they're not as big and fat as the animals living beneath the Antarctic sea ice," he says.

How to weigh a whale

How exactly do scientists know that the whales have become thinner? Do Fredrik Christiansen and his colleagues lift the huge animals out of the water with oversized weighing scales? No, he explains. Instead, the researchers have invented a method to work out the weight of the whales based on photographs taken by drones.

"Right whales like to lie flat on the sea surface. This makes them easy to photograph from above. When the drone has taken some photographs -- and we know the height of the drone -- we can calculate the size of the animal," he explains.

However, in order to know the weight of the whale, it is necessary to know the volume of the whale -- not just the length and width. But because scientists like Fredrik Christiansen have observed many right whales rolling around on the sea surface over the years -- and thereby have been able to measure their size -- the scientists now know the relationship between length, width and volume of the whales.

"We calculate the volume using the drone photographs -- and when we know the volume, we more or less know the weight. In this way, we can see that the whales have become thinner over the past 30 years -- and that's serious. The weight of the mothers has a huge impact on their calves," he says.

Small and weak whale calves

Thirty to forty years ago, the southern right whale had calves every three years on average. But this is no longer true, explains Fredrik Oscar Christiansen.

"In the 1980s, researchers observed that the right whales off the coast of South Africa gave birth to a new calf every three years. But because it's now difficult for them to fatten up during summer, this has fallen to every five years. This means that the population is growing significantly more slowly.

And not only do the whale calves come more rarely. The calves born today are smaller and grow more slowly.

"The amount of fat on the whale mother is directly linked to how much energy she can give to her calf through her milk. When the mother is thin, the calf gets less energy and grows more slowly," he says.

The researchers have discovered that the northern right whales in the waters off Canada and the northern US are not growing quite as big as before. This is possibly because the calves are born smaller. According to the researchers' calculations, a whale born in 2019 will be one metre shorter on average when it is fully grown than a whale born in 1981.

"Small calves have a higher risk of dying. They're more vulnerable if a killer whale attacks."

Hunted close to extinction

Right whales were given their name because they were considered the "right" whales to catch. People began hunting the large whales as early as in the 14th century, and for hundreds of years, they were hunted fiercely in both northern and southern parts of the Atlantic.

Oil from the whales' fat was one of the most important sources of energy. Train oil, which the oil used to be called, became a fuel in lamps -- both for indoors and for street lights. The demand for train oil was also one of the most important reasons why Denmark colonised Greenland in the 18th century.

Around 1900, train oil was replaced by another more efficient energy source: crude oil. The black gold pumped up from the underground meant that whale hunting was no longer profitable.

The southern right whale is one of the species that benefitted from the end of whaling. For more than 100 years, the population has been allowed to grow large and healthy again. And this is not just good for the whales, but also for the entire Southern Ocean ecosystem.

Because the whales bring nourishment to areas of the sea with little food.

Extremely important for the marine ecosystem

The sea around the Antarctic where the right whales come to eat has more life than any other sea on the planet. Despite the fact that the area only contains five per cent of the Earth's sea water, 20 per cent of all marine life lives in the area.

The many hours of sunshine in the summer, turbulent sea currents and the low temperature are perfect for teeming life.

The light makes marine algae grow explosively. The sea currents swirl the algae and nourishment around so that krill and plankton can gorge themselves. When full, the small crustaceans reproduce and form gigantic swarms. In some places, there may be as many as 35,000 krill in one cubic metre of water.

The right whales -- and many other animals -- stuff themselves with the abundance of krill, but unlike many other species, the whales migrate thousands of kilometres north to overwinter.

"The whales are extremely important for the parts of the sea where there is not much food. When the whales die, their huge bodies sink to the bottom. In the depths, they become food for a whole ecosystem of eel, sharks, crabs, lobsters, worms and microorganisms," says Fredrik Christiansen.

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Minke whales are as small as a lunge-feeding baleen whale can be

A new study of Antarctic minke whales reveals a minimum size limit for whales employing the highly efficient "lunge-feeding" strategy that enabled the blue whale to become the largest animal on Earth.

Lunge feeding whales accelerate toward a patch of prey, engulf a huge volume of water, and then filter out the prey through the baleen plates in their mouths. This strategy is used by the largest group of baleen whales, known as rorquals, which includes blue, fin, humpback, and minke whales.

The ability to engulf large amounts of prey-laden water is essential to making this feeding strategy pay off, and the energy efficiency increases with larger body size. An 80-ton blue whale, for example, can engulf a water volume equivalent to 135% of its body mass, whereas a 5-ton minke whale can engulf a volume equal to 42% of its body mass.

In the new study, published March 13 in Nature Ecology & Evolution, researchers used noninvasive suction tags to observe 23 Antarctic minke whales in the waters off the West Antarctic Peninsula, tracking their daytime and nighttime foraging behavior as they fed on Antarctic krill. Data from previous studies of krill-feeding humpback whales and blue whales were used for comparison.

"When we calculate how much energy they use in foraging and what their overall intake should be based on their size, we find that minke whales are right at the threshold," said first author David Cade, who led the study as a postdoctoral researcher at UC Santa Cruz and is now at Stanford's Hopkins Marine Station. "Anything smaller than a minke could not achieve the foraging rates necessary to survive."

Minke whales are not as well studied as other species of baleen whales, in part because they can be harder to find and tag.

"The data in this study represent more information on a poorly studied species than has ever been published previously and is helping us to better understand not only the species, but the role of baleen whales in marine ecosystems," said coauthor Ari Friedlaender, professor of ocean sciences at UC Santa Cruz. "With so little known about this species that is being impacted by climate change, the more we understand their ecology and behavior the better we can protect them."

The researchers observed remarkably high feeding rates for minke whales, especially at night, when they were often lunging every 15 seconds or so. Krill come to the surface at night and stay in the depths during the day, so daytime feeding requires deep dives, which are less efficient for smaller animals.

"During the day they feed at depths comparable to humpbacks and blue whales, but their foraging rates aren't as high because they're smaller," Cade said. "Their nighttime feeding rates are two to five times the day rate."

At night, the smaller, more maneuverable minke whales are well suited for pursuing small, scattered patches of krill at the surface. "When they're surface feeding, they don't have to hold their breath during dives and they can do lunges over and over again," Cade said. "Only at night can they get the really high feeding rates they need."

The study also addresses questions about the evolution of baleen whales and the origins of a feeding strategy that depends on large body size. Lunge feeding is thought to have arisen first in whales about the size of today's Antarctic minke whales. This enabled the evolution of whales with gigantic body sizes, such as blue whales, during the past 5 million years when changing ocean conditions led to the formation of predictable regions with large prey patches that could be efficiently exploited by lunge-feeding whales.

"Minke whales represent one extreme, at the small end of the spectrum, for how filter feeding in ocean predators evolved," Friedlaender said. "Understanding both the maximum and minimum size constraints on baleen whale size really helps us understand how this group of animals has evolved and how they affect and are impacted by marine ecosystems."

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Whales could be a valuable carbon sink, say scientists

Nature-based solutions to fight climate change take a holistic approach that promotes biodiversity and ecosystem preservation. While many efforts have focused on planting trees or restoring wetlands, researchers publishing in Trends in Ecology and Evolution on December 15 advocate for the importance of understanding the carbon sequestration potential of the planet's largest animals -- whales. In their paper, the researchers explore how these marine giants can influence the amount of carbon in our air and waters and potentially contribute to the overall reduction of atmospheric carbon dioxide.

"Understanding the role of whales in the carbon cycle is a dynamic and emerging field that may benefit both marine conservation and climate-change strategies," write the authors, led by Heidi Pearson, a biologist from the University of Alaska Southeast. "This will require interdisciplinary collaboration between marine ecologists, oceanographers, biogeochemists, carbon-cycle modelers, and economists."

Whales can weigh up to 150 tons, live over 100 years, and be the size of large airplanes. Like all living things, their hefty biomass is composed largely of carbon and they make up one of the largest living carbon pools in the pelagic ocean, part of the marine system that is responsible for storing 22% of Earth's total carbon.

"Their size and longevity allow whales to exert strong effects on the carbon cycle by storing carbon more effectively than small animals, ingesting extreme quantities of prey, and producing large volumes of waste products," write the authors. "Considering that baleen whales have some of the longest migrations on the planet, they potentially influence nutrient dynamics and carbon cycling over ocean-basin scales."

Whales consume up to 4% of their massive body weight in krill and photosynthetic plankton every day. For the blue whale, this equates to nearly 8,000 pounds. When they finish digesting their food, their excrement is rich in important nutrients that help these krill and plankton flourish, aiding in increased photosynthesis and carbon storage from the atmosphere.

A blue whale can live up to 90 years. When they die and their bodies fall to the seafloor, the carbon they contain is transferred to the deep sea as they decay. This supplements the biological carbon pump, where nutrients and chemicals are exchanged between the ocean and the atmosphere through complex biogeochemical pathways. Commercial hunting, the largest source of population decline, has decreased whale populations by 81%, with unknown effects on biological carbon pump.

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Sound reveals giant blue whales dance with the wind to find food

A study by MBARI researchers and their collaborators published today in Ecology Letters sheds new light on the movements of mysterious, endangered blue whales. The research team used a directional hydrophone on MBARI's underwater observatory, integrated with other advanced technologies, to listen for the booming vocalizations of blue whales. They used these sounds to track the movements of blue whales and learned that these ocean giants respond to changes in the wind.

Along California's Central Coast, spring and summer bring coastal upwelling. From March through July, seasonal winds push the top layer of water out to sea, allowing the cold water below to rise to the surface. The cooler, nutrient-rich water fuels blooms of tiny phytoplankton, jumpstarting the food web in Monterey Bay, from small shrimp-like krill all the way to giant whales. When the winds create an upwelling event, blue whales seek out the plumes of cooler water, where krill are most abundant. When upwelling stops, the whales move offshore into habitat that is transected by shipping lanes.

"This research and its underlying technologies are opening new windows into the complex, and beautiful, ecology of these endangered whales," said John Ryan, a biological oceanographer at MBARI and lead author of this study. "These findings demonstrate a new resource for managers seeking ways to better protect blue whales and other species."

The directional hydrophone is a specialized underwater microphone that records sounds and identifies the direction from which they originate. To use this technology to study blue whale movements, researchers needed to confirm that the hydrophone reliably tracked whales. This meant matching the acoustic bearings to a calling whale that was being tracked by GPS. With confidence in the acoustic methods established, the research team examined two years of acoustic tracking of the regional blue whale population.

This study built upon previous research led by MBARI Senior Scientist Kelly Benoit-Bird, which revealed that swarms of forage species -- anchovies and krill -- reacted to coastal upwelling. This time, researchers combined satellite and mooring data of upwelling conditions and echosounder data on krill aggregations with the acoustic tracks of foraging blue whales logged by the directional hydrophone.

"Previous work by the MBARI team found that when coastal upwelling was strongest, anchovies and krill formed dense swarms within upwelling plumes. Now, we've learned that blue whales track these dynamic plumes, where abundant food resources are available," explained Ryan.

Blue whales recognize when the wind is changing their habitat and identify places where upwelling aggregates their essential food -- krill. For a massive animal weighing up to 150 tonnes (165 tons), finding these dense aggregations is a matter of survival.

While scientists have long recognized that blue whales seasonally occupy Monterey Bay during the upwelling season, this research has revealed that the whales closely track the upwelling process on a very fine scale of both space (kilometers) and time (days to weeks).

"Tracking many individual wild animals simultaneously is challenging in any ecosystem. This is especially difficult in the open ocean, which is often opaque to us as human observers," said William Oestreich, previously a graduate student at Stanford University's Hopkins Marine Station and now a postdoctoral fellow at MBARI. "Integration of technologies to measure these whales' sounds enabled this important discovery about how groups of predators find food in a dynamic ocean. We're excited about the future discoveries we can make by eavesdropping on blue whales and other noisy ocean animals."

Background

Blue whales (Balaenoptera musculus) are the largest animals on Earth, but despite their large size, scientists still have many unanswered questions about their biology and ecology. These gentle giants seasonally gather in the Monterey Bay region to feed on small shrimp-like crustaceans called krill.

Blue whales are elusive animals. They can travel large distances underwater very quickly, making them challenging to track. MBARI researchers and collaborators employed a novel technique for tracking blue whales -- sound.

MBARI's MARS (Monterey Accelerated Research System) observatory offers a platform for studying the ocean in new ways. Funded by the National Science Foundation, the cabled observatory provides continuous power and data connectivity to support a variety of instruments for scientific experiments.

In 2015, MBARI researchers installed a hydrophone, or underwater microphone, on the observatory. The trove of acoustic data from the hydrophone has provided important insights into the ocean soundscape, from the migratory and feeding behaviors of blue whales to the impact of noise from human activities.

In 2019, MBARI and the Naval Postgraduate School installed a second hydrophone on the observatory. The directional hydrophone gives the direction from which a sound originated. This information can reveal spatial patterns for sounds underwater, identifying where sounds came from. By tracking the blue whales' B call -- the most powerful and prevalent vocalization among the regional blue whale population -- researchers could follow the movements of individual whales as they foraged within the region.

Researchers compared the directional hydrophone's recordings to data logged by tags that scientists from Stanford University had previously deployed on blue whales. Validating this new acoustic tracking method opens new opportunities for simultaneously logging the movements of multiple whales. It may also enable animal-borne tag research by helping researchers find whales to tag. "The integrated suite of technologies demonstrated in this paper represents a transformative tool kit for interdisciplinary research and mesoscale ecosystem monitoring that can be deployed at scale throughout protected marine habitats. This is a game changer and brings both cetacean biology and biological oceanography to the next level," said Jeremy Goldbogen, an associate professor at Stanford University's Hopkins Marine Station and a coauthor of the study.

This new methodology has implications not only for understanding how whales interact with their environment and one another but also for advancing management and conservation.

Despite protections, blue whales remain endangered, primarily from the risk of collisions with ships. This study showed that blue whales in Monterey Bay National Marine Sanctuary regularly occupy habitat transected by shipping lanes. Acoustic tracking of whales may provide real-time information for resource managers to mitigate risk, for example, through vessel speed reduction or rerouting during critical periods. "These kinds of integrated tools could allow us to spatially and temporally monitor, and eventually even predict, ephemeral biological hotspots. This promises to be a watershed advancement in the adaptive management of risks for protected and endangered species," said Brandon Southall, president and senior scientist for Southall Environmental Associates Inc. and a coauthor of the research study.

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Why whales don't get brain damage when they swim

Special blood vessels in whale brains may protect them from pulses, caused by swimming, in their blood that would damage the brain, new UBC research has suggested.

There are many theories as to the exact use of these networks of blood vessels cradling a whale's brain and spine, known as 'retia mirabilia', or 'wonderful net', but now UBC zoologists believe they've solved the mystery, with computer modeling backing their predictions.

Land mammals such as horses experience 'pulses' in their blood when galloping, where blood pressures inside the body go up and down on every stride. In a new study, lead author Dr. Margo Lillie and her team have suggested for the first time that the same phenomenon occurs in marine mammals that swim with dorso-ventral movements; in other words, whales. And, they may have found out just why whales avoid long-term damage to the brain for this.

In all mammals, average blood pressure is higher in arteries, or the blood exiting the heart, than in veins. This difference in pressure drives the blood flow in the body, including through the brain, says Dr. Lillie, a research associate emerita in the UBC department of zoology. However, locomotion can forcefully move blood, causing spikes in pressure, or 'pulses' to the brain. The difference in pressure between the blood entering and exiting the brain for these pulses can cause damage.

Long-term damage of this kind can lead to dementia in human beings, says Dr. Lillie. But while horses deal with the pulses by breathing in and out, whales hold their breath when diving and swimming. "So if cetaceans can't use their respiratory system to moderate pressure pulses, they must have found another way to deal with the problem," says Dr. Lillie.

Dr. Lillie and colleagues theorized that the retia use a 'pulse-transfer' mechanism to ensure there is no difference in blood pressure in the cetacean's brain during movement, on top of the average difference. Essentially, rather than dampening the pulses that occur in the blood, the retia transfer the pulse in the arterial blood entering the brain to the venous blood exiting, keeping the same 'amplitude' or strength of pulse, and so, avoiding any difference in pressure in the brain itself.

The researchers collected biomechanic parameters from 11 cetacean species, including, fluking frequency, and input these data into a computer model.

"Our hypothesis that swimming generates internal pressure pulses is new, and our model supports our prediction that locomotion-generated pressure pulses can be synchronized by a pulse transfer mechanism that reduces the pulsatility of resulting flow by up to 97 per cent,"says senior author Dr. Robert Shadwick, professor emeritus in the UBC department of zoology.

The model could potentially be used to ask questions about other animals and what's happening with their blood pressure pulses when they move, including humans, says Dr. Shadwick. And while the researchers say the hypothesis still needs to be tested directly by measuring blood pressures and flow in the brain of swimming cetaceans, this is currently not ethically and technically possible, as it would involve putting a probe in a live whale.

"As interesting as they are, they're essentially inaccessible," he says. "They are the biggest animals on the planet, possibly ever, and understanding how they manage to survive and live and do what they do is a fascinating piece of basic biology."

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New 3D model shows: Megalodon could eat prey the size of entire killer whales

Megalodon, the largest shark that ever lived, is famous for its huge, human-hand-sized teeth. However, there is little fossil evidence of its whole body. International researchers in collaboration with UZH used an exceptionally preserved specimen to create a 3D computer model of its full body. Their results suggest that the megalodon could fully consume prey the size of today's killer whales and then roam the seas without more food for two months.

The reconstructed megadolon (Otodus megalodon)was 16 meters long and weighed over 61 tons. It was estimated that it could swim at around 1.4 meters per second, require over 98,000 kilo calories every day and have stomach volume of almost 10,000 liters. These results suggest that the megalodon could travel long distances and was capable of eating whole prey of up to 8 meters long. This is notably the size of modern killer whales, today's top ocean predator. An ability to eat large apex predators of comparable size millions of years ago places megalodon at a higher trophic level than modern top predators.

Well-preserved spine enables reconstruction

These are the findings of an international study carried out in collaboration with the University of Zurich. The research was only possible thanks to the 3D modelling of one individual megalodon which was discovered in the 1860s. Against all odds, a sizeable portion of its vertebral column was left behind in the fossil record after the creature died in the Miocene oceans of Belgium at the age of 46 about 18 million years ago.

"Shark teeth are common fossils because of their hard composition which allows them to remain well preserved," says first author Jack Cooper, PhD student at Swansea University. "However, their skeletons are made of cartilage, so they rarely fossilize. The megalodon vertebral column from the Royal Belgian Institute of Natural Sciences is therefore a one-of-a-kind fossil."

From single vertebra to whole body mass

The research team, which includes researchers from Switzerland, UK, USA, Australia and South Africa, first measured and scanned every single vertebra, before reconstructing the entire column. They then attached the column to a 3D scan of a megalodon's dentition from the United States. They completed the model by adding "flesh" around the skeleton using a 3D-scan of the body of a great white shark from South Africa.

"Weight is one of the most important traits of any animal. For extinct animals we can estimate the body mass with modern 3D digital modelling methods and then establish the relationship between mass and other biological properties such as speed and energy usage," says co-author John Hutchinson, professor at the Royal Veterinary College in the UK.

A trans-oceanic super-apex predator

The high energetic demand would have been met by feeding on calorie-rich blubber of whales, in which megalodon bite marks have previously been found in the fossil record. An optimal foraging model of potential megalodon prey encounters found that eating a single 8-meter-long whale may have allowed the shark to swim thousands of miles across oceans without eating again for two months. "These results suggest that this giant shark was a trans-oceanic super-apex predator," says Catalina Pimiento, Professor at the University of Zurich and senior author of the study. "The extinction of this iconic giant shark likely impacted global nutrient transport and released large cetaceans from a strong predatory pressure."

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After thousands of years, an iconic whale confronts a new enemy

For millennia, vast expanses of the Arctic Ocean have been untouched by humans, ocean where narwhals and other marine mammals lived undisturbed. Now that climate change is causing sea ice to melt, there has been an uptick of human activity in the Arctic. This has resulted in significantly more noise from an array of human sources, including seismic surveys, mine blasts, port projects and cruise ships.

Although the noise is not violently loud when it comes a from a fair distance, for narwhals, the noise is disturbing and triggers stress -- even many kilometers away. These are the results of unique experiments conducted with the iconic whale. The University of Copenhagen has helped the Greenland Institute of Natural Resources (Pinngortitaleriffik) to analyse the data collected during the research.

Narwhals are notoriously difficult to study because they only live in the hard-to-reach High Arctic, which is often covered by ice. But the research team managed to tag a herd of narwhals in the Scoresby Sound fjord system of East Greenland using a variety of measurement equipment. They then positioned a ship in the fjord, which exposed the animals to noise -- both from the ship's engine and from a seismic airgun used for oil exploration.

"The narwhals' reactions indicate that they are frightened and stressed. They stop emitting the click sounds that they need to feed, they stop diving deep and they swim close to shore, a behaviour that they usually only display when feeling threatened by killer whales. This behavior means that they have no chance of finding food for as long as the noise persists," explains marine biologist Outi Tervo of the Greenland Institute of Natural Resources, who is one of the researchers behind the study.

Researchers can also see that the whales make an uncommon number of strokes with their tails when fleeing from a vessel. This may pose a danger to them because it vastly depletes their energy reserves. Constant energy conservation is important for narwhals as they need a great deal of oxygen to dive several hundred meters below the surface for food and return to the surface for air.

Everything in a narwhal's life is sound

Narwhals spend much of their time in the dark -- partly because the Arctic is dark for half of the year, and partly because these unicorns of the sea hunt at depths of up to 1800 meters, where there is no light. Thus, everything in a narwhal's life is based on sound. And like bats, they orient themselves by echolocation -- which includes emitting click sounds as they hunt.

"Our data shows that narwhals react to noise 20-30 kilometers away from a noise source by completely stopping their clicking sounds. And in one case, we could measure this from a source 40 kilometers away. It is quite surprising that we can measure how something so far away can influence whale behaviour," says Professor Susanne Ditlevsen of the University of Copenhagen's Department of Mathematical Sciences.

Professor Ditlevsen was responsible for the statistical analyses of the enormous and extremely complicated data sets that emerged from the experiments, where data was collected via underwater microphone, GPS, accelerometer (an apparatus that measures movement in three directions) and heart rate monitors. She continues:

"Even when a ship's noise is lower than the background noise in the ocean and we can no longer hear it with our advanced equipment, the whales can hear and distinguish it from other sounds in their midst. And so, to a degree, their behavior is clearly affected. This demonstrates how incredibly sensitive narwhals are."

Following a week of sonic tests, the researchers observed the whales' behavior return to normal again.

"But if they are exposed to noise for a long period of time -- for example, if a port is built nearby that leads to regular shipping traffic, the whales' success in hunting could be affected for a longer period of time, which could become quite serious for them. In this case, we fear that it could have physiological consequences for them and impair their fitness," says Outi Tervo.

Calling upon to authorities

The researchers' hope is that the authorities and other decision-makers will ensure for better management of the activities that create noise pollution in narwhal habitats.

"For the most part, narwhals live around Greenland, Canada and Svalbard in Norway. As such, these countries have the main responsibility for looking after them. Because narwhals are so well-adapted to the Arctic environment, they can't just choose to go to the Caribbean instead. It is being pressured both by warmer water temperatures and in some places, by fish catch. Now, noise enters the equation," says Susanne Ditlevsen.

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How do humpback whales rest?

An international research collaboration has used an omnidirectional camera attached to humpback whale to reveal how these creatures rest underwater. These findings demonstrate how wide-angle lens cameras can be useful tools for illuminating the ecology of difficult-to-observe animals in detail.

The research group consisted of Assistant Professor Takashi Iwata of Kobe University's Graduate School of Maritime Sciences, Researcher Martin Biuw of the Norwegian Institute of Marine Research, Assistant Professor Kagari Aoki and Professor Katsufumi Sato of the Atmosphere and Ocean Research Institute, the University of Tokyo, and Professor Patrick Miller of the University of St. Andrews.

These research results were published online in Behavioural Processes on February 25, 2021.

Main Points
 

• The researchers attached an omnidirectional (360°) camera to a humpback whale and discovered that these animals rest while drifting underwater. Whales can rest either on the surface or underwater, and it is believed that they choose which of these different environments to rest in depending on the situation.
• The omnidirectional camera recorded a wide range of information on the environment surrounding the tagged whale, revealing that humpback whales rest in groups rather than on their own.
• These results have demonstrated that animal-borne omnidirectional cameras are useful for learning more about animals that are difficult to observe.

Research Background

It is difficult to observe the ecology of marine animals directly as they spend the majority of their lives underwater. However, studies on the ecology of difficult-to-observe marine animals have been recently conducted using a method called bio-logging. This method involves attaching a camera to an animal and recording environmental information related to their behavior and surroundings. Various kinds of data can be recorded and measured, and this information can be used to understand aspects such as animal behavior and diving physiology. Such data includes depth, swimming speed, acceleration (which can be used to understand the animal's posture and detailed movements), vocalizations, heart rate and GPS (Global Positioning System) location data.

Cameras in particular are a powerful tool as they enable researchers to view the individual animal's surroundings, which in turn helps them to understand the animal's behavior. However, the camera's limited field of view has been an issue with animal-borne cameras up until now. For example, research using a camera attached to a humpback whale (Megaptera novaeangliae) revealed that the whale would quickly move away from foraging sites if a competitor was present. However, the competitor was not visible due to the limited scope of the camera, therefore its presence was merely assumed. A camera with a wide-angle lens is therefore necessary to film the animal's entire surroundings.

This research focused on the humpback whale, a species of baleen whale that is found in oceans around the globe. Using bio-logging, researchers have learned more about humpback whales' foraging habits, however little is known about their resting behaviors. Foraging events can be identified from the recorded depth, swimming speed and acceleration (movement) of the whale that are characteristic signs that it is chasing prey. However, researchers have not identified the characteristic signs of resting, and it is not understood what the differences are between resting and swimming slowly. Information about an animal's resting behavior is necessary in order to understand their ecology. For example, if we consider animal behaviors in terms of their time budget, the percentage of time for other activities such as foraging decreases if their resting periods increase. Even though information about resting behaviors is essential for understanding animal ecology, hardly anything is known about baleen whales' resting habits.

This research group used an omnidirectional camera (with a 360° field-of-view on land and a 270° field-of-view underwater) and a behavioral data logger in order to illuminate the resting behavior of humpback whales.

Research Methodology and Findings

RICOH supplied the basic THETA camera module for this research, which was made pressure-resistant and waterproofed using epoxy glue by Little Leonardo Corp., leading to the development of a new type of animal-borne omnidirectional camera. A suction cup tag was made out of buoyant materials that could be attached to the whale. The tag contained an omnidirectional camera, a behavioral data logger and a radio transmitter.

The field study was conducted in January 2016, off the Tromsø coast in Norway. To tag the whale, the researchers approached it in a small vessel (5-6m) and used a 6m pole to attach the tag to the animal. The tag was designed so that it would fall off naturally after several hours and float up to the surface. The tag was then recovered by determining its location via the signal from the transmitter.

The research team were able to tag one individual, obtaining around one hour of video data and approximately eleven hours of behavioral data. From the behavioral data, the researchers discovered that the whale was inactive during the first half of the recorded period and demonstrated active behavior in the latter half.

Based on past research, it was assumed that this active movement in the latter half was foraging activity. The video data was captured during the first half of the behavioral data recording period when the whale did not move much. In this videoed period, the tagged whale's deepest dive was 11m on average and its average swimming speed (cruising speed) was 0.75m/s-1. It has been reported that humpback whales' regular swimming speed is 1.45m/s-1, however the tagged whale was moving much more slowly during this period. Whales usually move their flukes (tails) when they swim but there were no signs that the individual whale moved its fluke in the behavioral data recorded during the videoed period. In the footage, two other whales that are drifting underwater without moving their flukes are visible. It was determined that the tagged individual was also drifting underwater from its slow swimming speed, lack of fluke movement and the continued presence in the video footage of other individuals that were drifting. Seal species, sperm whales and loggerhead turtles are known to drift underwater while they are resting. Therefore, it is believed that the tagged humpback whale in this study was also resting. Previous research has reported that baleen whale species rest on the surface but this study has revealed that they also rest while drifting underwater. It is thought that whales consider factors such as marine conditions and their own physical condition when choosing from the two different resting environments: on the surface or underwater. In addition, the footage from the omnidirectional camera shows that whales rest underwater in a group rather than on their own.

Further Research

Researchers have been using animal-borne cameras as a tool to investigate the ecology of marine animals. For example, a backwards-facing camera attached to a mother seal recorded images of a pup swimming behind her. However, to ascertain the significance of these images (for example, whether or not the mother was teaching the pup how to hunt) it is necessary to use a camera with a wide field of view so that we can obtain knowledge about the surrounding environment. Still camera images of touching behaviors between whales have also been recorded; however, a wide-lens camera would aid researchers in determining the frequency at which this behavior occurs. These examples show how necessary wide-lens cameras, such as omnidirectional cameras, are for investigating the ecology of marine animals. Such cameras enable researchers to record the environment surrounding the tagged animal, enabling them to determine whether other individuals (such as competitors, collaborators, or predators) are present or not, and understand the frequency and distribution of food sources.

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Killer whale grandmothers boost survival of calves

Pod of killer whales

Post-menopausal killer whale grandmothers improve the chances of survival for their grand-calves, new research has found.

The study found that grandmothers who were no longer able to reproduce had the biggest beneficial impact on the survival chances of their grand-offspring. This may be because grandmothers without calves of their own are free to focus time and resources on the latest generation, the researchers suggest.

The research team also found that grandmothers had a particularly important role in times of food scarcity, as the impact on a calf of losing a post-menopausal grandmother was highest in years when salmon was scarce.

Previous research has shown that post-reproductive female killer whales are the most knowledgeable and provide an important leadership role for the group when foraging in salmon grounds.

These benefits to the group may help to solve the long-standing mystery of why the menopause has evolved in some species of whales and in humans, the authors of the study say.

Senior author of the study, Dr Dan Franks from the Department of Biology, at the University of York, said: "The study suggests that breeding grandmothers are not able to provide the same level of support as grandmothers who no longer breed. This means that the evolution of menopause has increased a grandmother's capacity to help her grand-offspring.

"The death of a post-menopausal grandmother can have important repercussions for her family group, and this could prove to be an important consideration when assessing the future of these populations. As salmon populations continue to decline, grandmothers are likely to become even more important in these killer whale populations."

The study involved an international research team from the Universities of York and Exeter (UK), the Centre for Whale Research (USA) and Fisheries and Oceans Canada.

The scientists analysed 36 years of data gathered by the Center for Whale Research and Fisheries and Oceans Canada on two populations of resident killer whales. The populations (which include several pods, made up of multiple family groups) live off the North West Pacific Coast of Canada and the US and feed on Chinook salmon.

In resident killer whales, both sons and daughters stay with their mothers for life, but they mate with individuals from a different family group. Male killer whales typically have a shorter lifespan than females with many not surviving beyond 30 years. Females usually stop reproducing in their 30s-40s, but just like humans they can live for many decades following menopause.

Lead author, Dr Stuart Nattrass, from the University of York, added: "The findings help to explain factors that are driving the whales' survival and reproductive success, which is essential information given that the Southern Resident killer whales -- one of the whale populations under study -- is listed as endangered and at risk of extinction.

"We suspect when breeding grandmothers are supporting their own calves, their movement and activity patterns are constrained and they are not able to provide support and leadership in the same way as post-menopausal females. Also, grandmothers with their own calves will be busy caring for their own calves, and be able to invest less in their grand-offspring, compared to post-menopausal grandmothers.

We are currently conducting observational studies with drones to directly study helping behaviour between family members in these killer whales."

Co-author of the study, Prof Darren Croft from the University of Exeter, said "The menopause has only evolved in humans, killer whales and three other species of toothed whales and understanding why females of these species stop reproduction well before the end of life is a long standing evolutionary puzzle.

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