Southern right whale migration, new research


This 2011 video says about itself:

National Geographic photographer Brian Skerry describes a magical but risky experience photographing an enormous right whale off the coast of New Zealand.

From the British Antarctic Survey:

Migratory secrets of recovering whale species

May 19, 2020

Scientists have discovered where a whale species that feeds around the sub-Antarctic island of South Georgia breeds during the winter months. This understanding of where the animals migrate from will enable conservation efforts for their recovery from years of whaling. The results are published this week (20 May 2020) in the Journal of Heredity.

Southern right whales were hunted to near extinction after centuries of whaling. In the most comprehensive study of its kind, 30 researchers from 11 countries studied 15 skin samples from whales feeding around the sub-Antarctic island of South Georgia and compared them to 149 samples collected from around Argentina and Brazil and South Africa where the whales breed and give birth to their calves. New samples were collected from South Georgia during an expedition led by the British Antarctic Survey in 2018 and were combined with samples held by a network of collaborators across the globe.

Using a new genetic tool, the team discovered that most of the animals visiting South Georgia were calved around South America and not South Africa. This had previously been suspected, but not confirmed.

Lead author Dr Emma Carroll, from University of Auckland says: “Genetic methods are important in linking whale breeding grounds, areas that are closely monitored for population recovery, with feeding areas that are being and will be impacted by climate change. It is only by understanding these links that we can understand how whale populations will fare in a changing world.”

Collaborating with Chilean colleagues, the team also analysed the first-ever DNA sample from the Critically Endangered Chile-Peru southern right whale population. They found genetically, the Chile-Peru whale is a mixture between Indo-Pacific and Atlantic calving grounds, suggesting Chile-Peru has acted as a ‘stepping stone’ between these two areas.

Whale ecologist and senior author Dr Jennifer Jackson, at British Antarctic Survey, who led the project, says: “This is an important part of the jigsaw in understanding the geographical range of southern right whales. Identifying the migratory links of recovering whale populations is crucial to build accurate assessments of how well whale populations are recovering, and to understand how vulnerable these populations are to anthropogenic threats through their life cycle.

“There have been unexplained high whale calf mortalities around Argentina in the Península Valdéz region over the last 17 years, so there is a lot of work to be done to protect this species throughout their migratory range.”

The team are also tracking the movements of two South Georgia right whales in real time using satellite tags. One whale is already migrating towards the South American coast, providing further evidence of the migratory connection. Follow these whales here.

Notes

  • Southern right whales were so named because they were the ‘right’ whale to hunt, and in the South Atlantic they have been heavily exploited for over 350 years, with catches peaking in the mid 1800s. Only in the past three decades, have southern right whales again become regular winter visitors to Argentina, Brazil and South Africa, where they use sheltered bays to calve. Another population to the west, in Chile and Peru, has not fared so well, and the lack of recovery from whaling has led this population to be declared ‘Critically Endangered’ by the IUCN.
  • In 2009, the global estimate of southern right whales was estimated as 13,611 and the calving grounds in Argentina and Brazil was 4,029.
  • The Wild Water Whales project has been running since December 2016, and focusses on studying the population recovery and health of southern right whales in South Georgia waters. The project involves sightings surveys, using acoustic methods to find whales, collecting photo-identifications and skin samples to identify individuals, tracking whales to find out where they feed, and studying the health condition of right whales using drone technology.
  • Historically, the seas around South Georgia are a key feeding ground for multiple whale species, including the southern right, humpback, blue and fin whales. The area is abundant with food in summer, namely krill, a shrimp-like crustacean, which provides a key part of their diet.
  • Led by British Antarctic Survey, the South Georgia Wild Water Whales project has been funded by an EU BEST Medium grant, the Darwin Initiative, South Georgia Heritage Trust, Friends of South Georgia Island and the World Wildlife Fund.
  • The project used a new genetic tool for population visualisation and assignment (GENEPLOT) which estimated how well for example samples from South Georgia could be assigned to wintering ground datasets from Brazil, Argentina and South Africa.

How prehistoric whales died, video


This 29 April 2020 video says axbout Chile about itself:

How the Andes Mountains Might Have Killed a Bunch of Whales

At a site known as Cerro Ballena or Whale Hill, there are more than 40 skeletons of marine mammals — a graveyard of ocean life dating back 6.5 million to 9 million years ago, in the Late Miocene Epoch. But the identity of the killer that they finally settled on might surprise you.

Oregon, USA gray whales’ health research


This 2017 video is called Drone Footage Over Whales / Depoe Bay, Oregon.

From Oregon State University in the USA:

Three years of monitoring of Oregon’s gray whales shows changes in health

April 27, 2020

Three years of “health check-ups” on Oregon’s summer resident gray whales shows a compelling relationship between whales’ overall body condition and changing ocean conditions that likely limited availability of prey for the mammals, a new study from Oregon State University indicates.

Researchers from the Geospatial Ecology of Marine Megafauna Laboratory at OSU’s Marine Mammal Institute used drones to monitor 171 whales off the Oregon Coast during the foraging season between June and October in 2016, 2017 and 2018.

They found that the whales’ health declined following a period of relatively poor upwelling — an ocean condition that brings colder, nutrient-rich water closer to the surface — compared to previous years.

“What we see is this compelling relationship between the oceanographic processes that control the quality and quantity of available prey and whale health,” said Leigh Torres, an assistant professor with the Marine Mammal Institute and the lab’s director. “This research gives us an inclination that changes in ocean conditions might be causing skinny whales.”

The findings may also provide insight into the unusual gray whale die-off event that occurred in 2019 along the Pacific Coast, Torres said. More than 200 gray whales were reported dead between Mexico and Alaska last year, including six in Oregon. Many of the deceased whales appeared to be in poor body condition, meaning they looked skinny.

The study was just published in the journal Ecosphere. The paper’s lead author is Leila Soledade Lemos, who recently completed her doctorate at Oregon State and worked with Torres in the GEMM Lab.

Most gray whales migrate from breeding grounds in Mexico to feeding grounds in the Bering and Chukchi seas between Alaska and Russia, where they spend the summer. The Pacific Coast Feeding Group, as Oregon’s gray whales are known, spend the summer months feeding in coastal waters of Oregon, as well as northern California, Washington and southern Canada.

Torres and her team conduct “health check-ups” on the whales using drones to capture images and nets to capture fecal samples — two methods that provide researchers a lot of information in a noninvasive way, reducing stress on the whales.

Lemos used images captured by the drones to calculate the whales’ Body Area Index. The BAI is similar to the Body Mass Index, or BMI, in humans, because both allow for comparisons among individuals despite differences in length and height.

The Body Area Index is a measurement that allows researchers to compare changes in individual whales as well as the population as a whole during the course of the feeding season and from year to year. The fecal samples help researchers determine a whale’s hormones, sex and diet.

Gray whales typically arrive on the foraging grounds on the skinny side, then in ideal conditions will bulk up over the course of the summer in preparation for migration and breeding.

“With this research, we’re trying to understand more about the health of the whales and how it varies throughout the foraging season and from year to year,” Torres said. “Once we establish a baseline for whale body condition, we can start to see what is healthy and what is not and why.”

The researchers often encounter the same whales multiple times in a season, or from one year to another, and have gotten to know their markings and features well enough to spot the whales by the names they’ve been assigned, such as Spray, Knife and Clouds.

“The first year the whales looked really fat and healthy. But after 2016, the whales were really skinny. You could see their skeletons,” Lemos said. “For these whales, body condition is strongly related to food availability. It is also related to when they invest in reproduction.”

The researchers noted nine pairs of mothers and calves in 2016, but only one pair each in the two following years. Calves had the highest Body Area Index numbers, followed by pregnant females. Lactating females had the lowest BAI and the most depleted body condition.

Overall, the whales’ body condition deteriorated after poor upwelling conditions between 2016 and mid-2018. In 2016, the whales’ mean BAI was 40.82, while in 2017 it was 38.67; 2018 was similar to 2017, at 38.62.

The poor upwelling may have caused a shift in the availability or quality of zooplankton, the whales’ primary prey. But the impact of the changing food supply really became noticeable a year after the poor upwelling condition began.

“There was a one-year lag, or carry-over, between the lack of prey in 2016 and the whales’ body condition the next year,” Torres said.

One of the whales that died during the 2019 event had been observed and catalogued in previous years by Oregon State researchers.

The study highlights the value of monitoring whale health over time, Torres said. The researchers now have four years of data on Oregon’s resident whales and hope to continue monitoring them to better understand health patterns in the population and how they connect to changing ocean conditions.

Northern and Southern right whales, new research


This 4 September 2016 video says about itself:

A Rare White Southern Right Whale Calf Has Been Filmed For The First Time

Researchers from Murdoch University’s Cetacean Research Unit (MUCRU) have recorded extraordinary video footage of a rare white southern right whale calf off the coast of Western Australia. The research team used a suite of innovative technologies including suction cup tags and drones to assess fine-scale movements, acoustic communications, ambient noise, calf suckling rates and body condition of southern right whales.

From the Woods Hole Oceanographic Institution in the USA:

North Atlantic right whales are in much poorer condition than Southern right whales

April 23, 2020

New research by an international team of scientists reveals that endangered North Atlantic right whales are in much poorer body condition than their counterparts in the southern hemisphere.

This alarming research, led by Dr. Fredrik Christiansen from Aarhus University in Denmark, was published this week in the journal Marine Ecology Progress Series. The study is the result of a collaborative effort by scientists from 12 institutions across 5 nations. Among the coauthors are Senior Scientist Peter Corkeron and Associate Scientist Heather Pettis of the Anderson Cabot Center for Ocean Life at the New England Aquarium and Michael Moore and Carolyn Miller of the Woods Hole Oceanographic Institution.

The analyses revealed that individual North Atlantic right whales — juveniles, adults and mothers — were all in poorer body condition than individual whales from the three populations of Southern right whales. This is alarming, since poor body condition for North Atlantic right whales helps explain why too many of them are dying and why they are not giving birth to enough calves. It could also be affecting their growth and delaying juveniles reaching sexual maturity. These combined impacts on individuals help explain why the species is in decline.

Since the cessation of large-scale commercial whaling in the last century, most populations of southern right whales have recovered well. Now there are about 10,000-15,000 southern right whales. Unfortunately, the same cannot be said for the North Atlantic right whales, found today mostly off the east coast of North America. There are now around 410 individuals left, and the species is heading to extinction. Lethal vessel strikes and entanglement in fishing gear continue to kill these whales. Individual North Atlantic right whales also have to cope with the energetic expense and other costs that are caused by frequent entanglements in fishing gear, in particular lobster and crab pots. These burdens, along with a change in the abundance and distribution of the rice-sized plankton that they eat, have left these whales thin and unhealthy, which makes them less likely to have a calf. This, in turn, contributes to the current overall decline of the species. To quantify “thin and unhealthy”, Dr. Christiansen and his colleagues investigated the body condition of individual North Atlantic right whales and compared their condition with individuals from three increasing populations of Southern right whales: off Argentina, Australia and New Zealand.

“Good body condition and abundant fat reserves are crucial for the reproduction of large whales, including right whales, as the animals rely on these energy stores during the breeding season when they are mostly fasting,” said Dr. Christiansen. Stored fat reserves are particularly important for mothers, who need the extra energy to support the growth of their newly born calf while they are nursing.

The study is the largest assessment of the body condition of baleen whales in the world. The international research team used drones and a method called aerial photogrammetry to measure the body length and width of individual right whales in these four regions around the world. From aerial photographs, the researchers estimated the body volume of individual whales, which they then used to derive an index of body condition or relative fatness.

“This started out as a conversation between a few of us over dinner at a conference in 2015. Now that the results are out, they’re quite shocking,” said Peter Corkeron of the Anderson Cabot Center for Ocean Life at the New England Aquarium. “We know that North Atlantic right whales as a species are doing poorly, but this work brings home that as individuals, they’re also doing poorly. Their decline has been so rapid that we know it’s not simply because not enough calves are being born — too many whales are also dying from human-caused injuries. But this study also shows that their decline isn’t solely due to these deaths. Their problems are more insidious, and we need to find a way to ensure that the health of all individual whales improves.”

“For North Atlantic right whales as individuals, and as a species, things are going terribly wrong. This comparison with their southern hemisphere relatives shows that most individual North Atlantic right whales are in much worse condition than they should be,” said Michael Moore from the Woods Hole Oceanographic Institution. “As a veterinarian, I’ve long been concerned about how entanglements affect the welfare of these whales. Now we are starting to draw the linkages from welfare to this species’ decline. Sub-lethal entanglement trauma, along with changing food supplies is making them too skinny to reproduce well, and lethal entanglement and vessel trauma are killing them. To reverse these changes, we must: redirect vessels away from, and reduce their speed in, right whale habitat; retrieve crab and lobster traps without rope in the water column using available technologies; and minimize ocean noise from its many sources.”

This work was supported by funding from NOAA, US Office of Naval Research Marine Mammals Program, World Wildlife Fund for Nature Australia, Murdoch University School of Veterinary and Life Sciences, New Zealand Antarctic Research institute, Otago University and New Zealand Whale and Dolphin Trust and Argentina National Geographic Society.

For 40 years, the New England Aquarium’s right whale team has extensively researched and tracked individual right whales and curates the North Atlantic Right Whale Catalog. The scientific team monitors the whales’ arrival at breeding and feeding grounds, registering new calves, death rates, and also measuring changes in stress and reproductive hormones.

The Woods Hole Oceanographic Institution is dedicated to advancing knowledge of the ocean and its connection with the Earth system through a sustained commitment to excellence in science, engineering and education, and to the application of this knowledge to problems facing society.

New Zealand blue whales feeding, new research


This 2017 video from New Zealand is called See Blue Whales Lunge For Dinner in Beautiful Drone Footage | National Geographic.

From Oregon State University in the USA:

Surface feeding could provide more than just snacks for New Zealand blue whales

April 22, 2020

Feeding at the ocean’s surface appears to play an important role in New Zealand blue whales’ foraging strategy, allowing them to optimize their energy use, Oregon State University researchers suggest in a new study.

Blue whales are the largest mammals on Earth. Because of their enormous size, the whales must carefully balance the energy gained through their food intake with the energetic costs of feeding, such as diving, holding their breath or opening their mouths, which slows their movement in the water. Adding to the challenge: their prey are tiny krill and they must find and eat large volumes of them to make any energetic headway.

“People think about whales having to dive deep to get to the densest prey patches, but if they can find their prey in shallow waters, it’s actually more energetically profitable to feed near the surface,” said Leigh Torres, an assistant professor and director of the Geospatial Ecology of Marine Megafauna Laboratory at OSU’s Marine Mammal Institute. “In this population of whales in New Zealand, they foraged more in areas where their prey was dense and shallow.

“Their dives were relatively short, and they were feeding more at the surface, which requires less energy.”

The findings were published today in the journal PeerJ. Co-authors of the study include Dawn Barlow, a doctoral student in Torres’ lab; Todd Chandler, who captured drone footage used in the study; and Jonathan Burnett of OSU’s Aerial Information Systems Laboratory.

Much of what researchers know about blue whale foraging comes from tags placed on whales, which can record travel and diving patterns, including acceleration, or lunging, toward patches of food. But surface feeding is not as well understood, in part because it is harder to analyze tag data and quantify the size of prey patches at the water’s surface, Barlow said.

During a field research trip to study blue whales off the coast of New Zealand in 2017, Torres and her team observed surface feeding from their boat on multiple occasions. They also noted that the density of krill patches was greater closer to the water’s surface.

The researchers collected data that showed blue whales had relatively short dive times overall, about 2.5 minutes, compared to other blue whale populations, such as those off the coast of California, which average dives of about 10 minutes. When surface foraging was observed, the dive time of New Zealand blue whales dropped even more, to 1.75 minutes.

Using a drone, the researchers captured video of a blue whale surface feeding on a patch of krill. The footage illustrates a blue whale’s feeding process, including decision-making about whether or not to eat patches of krill near the ocean’s surface. The video, which was first shared publicly shortly after the research trip, went viral online. It also gave researchers another source of data to describe surface feeding behavior.

“The drone footage fills a gap in our understanding of surface feeding,” Barlow said.

Through the footage, the researchers were able to see how the whale used its right eye to target the prey. They were able to quantify the recognition distance from the whale to the prey and could measure how widely the whale opened its mouth to feed. The footage also showed the whale’s decision to rotate from one side to the other to better capture the krill.

“The video allows us to describe a lot of really cool kinematics and body movement coordination by the whale that we haven’t been able to see before,” Torres said.

“The footage also allowed us to see the prey response in new way. We can see when the krill begin to flee as the whale approaches, which is really amazing. At the whale’s fastest speed and acceleration, the krill begin to jump away just eight-tenths of a second before the whale strikes at the krill patch.”

Though the researchers had surface feeding footage from just one whale, the footage included four encounters between that whale and surface prey patches, providing insight into decision-making processes by the whale in response to the size and orientation of the prey patches, Torres said.

“This footage highlights the value of using drones for study and observation of whales,” she said. “Drone footage could be a good complement to data collected from tags for studying surface behaviors of whales.”

Humpback whales off Chile


This 21 March 2020 video says about itself:

Humpback whales thrive off the tip of Chile

Humpback whales have found a safe haven on the tip of Chile. Bad weather means the region is relatively untouched by humans. Humpback whale populations have grown five-fold in Francisco Coloane Marine Park. Almost 20 years ago biologists only counted 40 individuals in the park. Now, they’ve counted 190.

Globally there are around 87 cetacean species, and conservation efforts to protect humpback whales have been among the most successful. Hunting humpback whales has been banned since the ‘60s.

Read more here.

Researchers recommend new guidelines for noise levels from whale-watching boats after having carried out experiments with humpback whales. They exposed the whales to different levels of boat-engine noises while observing the current guidelines for whale-watching — keeping 100 meters distance, for instance — while monitoring the whales’ behavior closely with a drone camera. The researchers concluded that the noise level from a boat’s engine should stay below 150 decibels: here.

Narwhal tusks and sexuality, new research


This 2018 video says about itself:

There’s a lot of mystery that surrounds narwhals. We here to set the record straight on these fascinating creatures.

From Arizona State University in the USA:

For narwhals, the ‘unicorn of the seas’, size matters for sexual selection

March 17, 2020

Showy peacock feathers, extravagant elk antlers and powerful crayfish claws are just a few examples of the ostentatious animal extremes used to compete for and attract mates, a process called sexual selection.

Now, thanks to Arizona State University researcher Zackary Graham and his colleagues, we can add the “unicorn of the seas, the narwhal, to the list.

“Broadly, I’m interested in sexual selection, which is responsible for creating some of the craziest traits in biology. As an evolutionary biologist, I try to understand why some animals have these bizarre traits, and why some don’t”, said Graham, a doctoral student at ASU’s School of Life Sciences.

“One way we try to understand these traits is by looking at the morphology, or the size and shape of them. I immediately became obsessed with trying to think of some interesting animals to study. I was Googling everything; maybe I can find a dinosaur in a museum. Eventually, I found the narwhal tusk.”

Graham is the lead author of a new study which demonstrates the best evidence to date that the narwhal tusk functions as a sexual trait, published online in the journal Biology Letters.

A tusk among us

Like walruses and elephants, male narwhals (Monodon monoceros) grow tusks; these are modified teeth. In narwhals, the left tooth erupts from their head, reaching more than 8-feet-long in some individuals. The tusk grows out in a spiral pattern, giving the appearance of a sea-dwelling unicorn.

Since narwhals spend most of their lives hidden under the Arctic ice, there has been much speculation on what exactly the tusk is used for: hunting, fighting or perhaps something more amorous in nature?

Graham mentions that there have been reports of head scarring, broken tusks and tusks impaled in the sides of males, who may have been on the receiving end of some aggression. Other scattered observations include a behavior of “tusking”, where two narwhals cross and rub their tusks together, suggests that the tusk is used for communication during intra- or intersexual interactions.

Graham has studied sexual selection in all sorts of species, including the crayfish he studies for his PhD dissertation. He realized, that to demonstrate that the tusk is sexually selected, he could use the relationship between tusk size with body size to understand this mysterious trait. To do so, his team collected morphology data on 245 adult male narwhals over the course of 35 years.

With colleagues Alexandre V. Palaoro of the LUTA do Departamento de Ecologia e Biologia Evolutiva, UNIFESP, Brazil, and Mads Peter Heide-Jørgensen and Eva Garde, from the Greenland Institute of Natural Resources, they created a large dataset from the carefully curated narwhal field data.

When comparing individuals of the same age, sexually selected traits often exhibit disproportional growth — that is, for a given body size, sexually selected traits are often larger than expected in the largest individuals. Importantly, they compared the growth (or scaling) of the tusk to the scaling relationship between body size and a trait that is unlikely to have sexual functions. To do so, they used the tail of the narwhals, called the fluke.

“We also predicted that if the narwhal tusk is sexually selected, we expect greater variation in tusk length compared to the variation in fluke width,” said Graham. This is because many sexual traits are highly sensitive to nutrient and body condition, such that only the biggest and strongest individuals can afford the energy to produce extremely large traits.

According to Graham, they found that male tusks can have over 4-fold variation in tusk length (the same body size males can have tusks ranging from 1.5-feet to 8.2-feet) long. However, the fluke hardly varies at all, ranging from 1.5-feet to 3-feet long within individuals of the same body size. They also found disproportional growth in the tusk compared to the fluke. Based on the disproportional growth and large variation in tusk length they found, they have provided the best evidence to date that narwhal tusks are indeed sexually selected.

“By combining our results on tusk scaling with known material properties of the tusk, we suggest that the narwhal tusk is a sexually selected signal that is used during the male-male tusking contests,” said Graham. “The information that the tusk communicates is simple: “I am bigger than you.””

And if only the highest quality males produce and adorn the largest tusks, then the tusk likely serves as an honest signal of quality to females or males.

Under the Ice

Graham hopes that future researchers will use aerial and aquatic drones to provide concrete evidence of the tusk function in nature and elucidate the tusks exact role as either an aggressive weapon, a sexual signal or both.

Perhaps one day, we can look forward to a “Big Love: Narwhals Under the Ice” nature documentary coming to an IMAX near you.

“Overall, our evidence supports the hypothesis that the tusk functions both as a sexually selected weapon and sexually selected signal during male-male contests,” said Graham. “However, further evaluations of the narwhal’s ecology are warranted.”

Why whales, dolphins swim so well


This 2015 video says about itself:

DOLPHINS & WHALES

Ute Margreff lives on Ireland’s Atlantic coast, Florian Graner in the Puget Sound in the Northwest of the USA. Both Germans share a deep passion for the sea and its creatures. About 10 years ago Ute Margreff got to know the female solitary dolphin Mara – it was the start of an unusual friendship. Florian Graner found its private paradise close to Seattle. Right in front of his doorstep he dives into a world inhabited by sea lions, giant octopus and orca whales. Both Ute and Florian fight for the protection of marine habitats, each one in a different and very unique way.

From Lehigh University in the USA:

Secrets to swimming efficiency of whales, dolphins

March 19, 2020

Summary: Recent work has examined the fluid mechanics of cetacean propulsion by numerically simulating their oscillating tail fins. A team developed a model that, for the first time, could quantitatively predict how the motions of the fin should be tailored to its shape in order to maximize its efficiency. The research could influence the design of next-gen underwater robots.

Someday, underwater robots may so closely mimic creatures like fish that they’ll fool not only the real animals themselves but humans as well. That ability could yield information ranging from the health of fish stocks to the location of foreign watercraft.

Such robots would need to be fast, efficient, highly maneuverable, and acoustically stealthy. In other words, they would have to be very much like bottlenose dolphins or killer whales.

“We’re interested in developing the next generation of underwater vehicles so we’re trying to understand how dolphins and whales swim as efficiently as they do,” says Keith W. Moored, an assistant professor of mechanical engineering and mechanics in Lehigh University’s P.C. Rossin College of Engineering and Applied Science. “We’re studying how these animals are designed and what’s beneficial about that design in terms of their swimming performance, or the fluid mechanics of how they swim.”

Moored is the principal investigator on a paper recently published in the Journal of the Royal Society Interface that examined the fluid mechanics of cetacean propulsion by numerically simulating their oscillating tail fins. For the first time, Moore and his team were able to develop a model that could quantitatively predict how the motions of the fin should be tailored to its shape to maximize its efficiency. The research was part of a larger project supported by the Office of Naval Research under its Multidisciplinary University Research Initiative program. The project, which received more than $7 million in funding (with $1 million going to Lehigh) over more than five years, also included the University of Virginia, West Chester University, Princeton University, and Harvard University.

The tail fins of cetaceans (whales and dolphins) come in a wide variety of shapes. The way these animals move their fins, or their kinematics, also varies. Some cetaceans may flap their fins at a greater amplitude, or pitch them at a steeper angle. Moored and his team wanted to better understand this interplay between the two variables to determine if tail fin shape was tailored to a specific set of kinematics.

Using the shape and kinematic data for five cetacean species (with common names of bottlenose dolphin, spotted dolphin, killer whale, false killer whale, and beluga whale), they ran simulations on each of the species to determine its propulsive efficiency. Then they swapped the data around, for example, running a simulation on the fin shape of a killer whale attached to the kinematics of a dolphin.

“We ran 25 of these swapped simulations, and we were really surprised,” says Moored. “The pseudo orca fin shape was always the best, meaning it was the most efficient. It didn’t matter what kinematics we gave it. And the beluga whale kinematics were always the best, regardless of which shape it was attached to. We didn’t expect that, so we started digging into it more and developed this relatively simplistic model of how efficiency scales with different kinematic and shape variables.”

The model worked well to capture the data that Moored and his team had already generated, so they extended their data set to examine any resulting trends. They found that their model not only predicted efficiency beyond their data set but also revealed that specific shapes were tailored to specific kinematics.

One interesting revelation, says Moored, was the fundamental interplay between circulatory forces and added mass forces that contribute to an animal’s movement. Circulatory forces are those that generate lift, like with aircraft.

“A tail that’s flapping up and down generates forces just like an aircraft, but it also generates added mass forces that have to do with how fast the fluid is being accelerated,” says Moored. “In the past, people didn’t think those added mass forces were that relevant in cetacean swimming. It’s not acknowledged at all in the previous literature. But we found that the accelerations of the fin are integral to predicting the trends of efficiency, and that was fascinating to us. It ultimately gives us a predictive model that’s accurate. Without it, we’d basically be saying that fin shape doesn’t change the efficiency, and that’s not true.”

Having a model that can predict performance based on shape and kinematics provides a basic design equation of sorts for building an underwater robot that performs like a cetacean. To date, these equations haven’t existed. And the potential for these machines is huge. Fast, efficient, and highly maneuverable fish-shaped robots could help researchers test hypotheses about how the animals swim, and better understand the behavior of fish schools. They could be used to detect submarines and other submersibles. They could also be used to monitor the impact of climate change on fish stock populations.

Moored and his team have already moved on and expanded their scaling model to account for a larger range of variables they then validated with experimental data. Ultimately, they want to build a far more predictive model. One that captures the effects of these variables, and can then predict performance for a range of applications.

“This fish swimming problem is a really exciting problem because it’s so complicated,” he says. “It’s fascinating to take this chaos of variables and see order in it, to see the structure in it, and to understand what’s fundamentally happening.”

Sharks and whales, video


This 3 March 2020 video says about itself:

A Deep Dive Into the Lives of Sharks and Whales

Join us for a deep dive into the world of sharks and orcas. In this reel, we meet people who study, swim with and photograph these fascinating mammals, from the warm waters of Bimini to the frigid Arctic Ocean.