Dolphins are attracted to magnets: Add dolphins to the list of magnetosensitive animals, French researchers say

Bottlenose dolphins

Add dolphins to the list of magnetosensitive animals, French researchers say. Dolphins are indeed sensitive to magnetic stimuli, as they behave differently when swimming near magnetized objects. So says Dorothee Kremers and her colleagues at Ethos unit of the Université de Rennes in France, in a study in Springer's journal Naturwissenschaften -- The Science of Nature. Their research, conducted in the delphinarium of Planète Sauvage in France, provides experimental behavioral proof that these marine animals are magnetoreceptive.

Magnetoreception implies the ability to perceive a magnetic field. It is supposed to play an important role in how some land and aquatic species orientate and navigate themselves. Some observations of the migration routes of free-ranging cetaceans, such as whales, dolphins and porpoises, and their stranding sites suggested that they may also be sensitive to geomagnetic fields.

Because experimental evidence in this regard has been lacking, Kremers and her colleagues set out to study the behavior of six bottlenose dolphins in the delphinarium of Planète Sauvage in Port-Saint-Père. This outdoor facility consists of four pools, covering 2,000 m² of water surface. They watched the animals' spontaneous reaction to a barrel containing a strongly magnetized block or a demagnetized one. Except from this characteristic, the blocks were identical in form and density. The barrels were therefore indistinguishable as far as echolocation was concerned, the method by which dolphins locate objects by bouncing sound waves off them.

During the experimental sessions, the animals were free to swim in and out of the pool where the barrel was installed. All six dolphins were studied simultaneously, while all group members were free to interact at any time with the barrel during a given session. The person who was assigned the job to place the barrels in the pools did not know whether it was magnetized or not. This was also true for the person who analyzed the videos showing how the various dolphins reacted to the barrels.

The analyses of Ethos team revealed that the dolphins approached the barrel much faster when it contained a strongly magnetized block than when it contained a similar not magnetized one. However, the dolphins did not interact with both types of barrels differently. They may therefore have been more intrigued than physically drawn to the barrel with the magnetized block.

"Dolphins are able to discriminate between objects based on their magnetic properties, which is a prerequisite for magnetoreception-based navigation," says Kremers. "Our results provide new, experimentally obtained evidence that cetaceans have a magenetic sense, and should therefore be added to the list of magnetosensitive species."

Source: Springer Science+Business Media

The science behind swimming: From whales to larvae, common principles at work in swimming

Whale and diver (stock illustration). Using simple hydrodynamics, researchers were able to show that a handful of principles govern how virtually every animal -- from the tiniest fish to birds to gigantic whales propel themselves though the water. Credit: © James Thew / Fotolia

At nearly 100 feet long and weighing as much as 170 tons, the blue whale is the largest creature on the planet, and by far the heaviest living thing ever seen on Earth. So there's no way it could have anything in common with the tiniest fish larvae, which measure millimeters in length and tip the scales at a fraction of a gram, right?

Not so fast, says L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics.

Using simple hydrodynamics, a team of researchers led by Mahadevan was able to show that a handful of principles govern how virtually every animal -- from the tiniest fish to birds to gigantic whales propel themselves though the water. The study is described in a September 14 paper in Nature Physics.

"What we wanted to investigate was how the speed of an organism changes as a function of how large it is, how quickly it moves and how much it moves," Mahadevan said. "To resolve that in detail, however, is very complex, because there is a great deal of differences in morphology and what parts of the body different creatures use to swim. The question is: Is there anything in common across all these organisms? The answer, we found, is yes."

In an effort to uncover those common principles, Mahadevan working with a postdoctoral fellow in his group , Mattia Gazzola, and a colleague Mederic Argentina from the University of Nice, began by trying to unpack the physics of how different creatures swim.

"The traditional approach to swimming phenomena is to take a certain specimen and accurately characterize it via experiments and/or simulations, and try to generalize from there, but it is very hard to strip out specific biological effects from general principles," Gazzola said. "We instead thought that while swimmers exhibit a huge diversity in shapes and kinematics, at the end of the day they all live in the same media, water.

"Therefore we thought that if a unifying mechanistic principle existed, it had to lie in the constraints that the flow environment poses to all its inhabitants," he continued. "And this is a purely physical problem, much easier to solve since it is not affected by biological vagaries. What I like about this paper is that in one line of algebra we derived a compact formula that accounts for 50 years of experiments. This is an example of how powerful minimal modeling can be."

"The basic relationship we wanted to understand was how the input variables -- namely the size of the organism, the amount an organism moves and how quickly it moves -- control the output variable, which is effectively the speed at which it moves," Mahadevan explained. "What we found is that there is a specific relationship, which can be described by in terms of a simple scaling law with two limits."

The first, which corresponds to creatures moving at intermediate speeds, describes situations where the bulk of the resistance is caused by skin friction, because water "sticks" to the organism's body. At faster speeds, Mahadevan said, the resistance organisms face largely comes from pressure that builds up in front of and around them, which is described by the second limit.

"While it wasn't a surprise that the resistance changed at organisms moved faster, the fact that those challenges could be so simply described was interesting and provocative, because we are talking about organisms that range in size from a few millimeters to the size of a blue whale," Mahadevan said.

Armed with those observations, Mahadevan and colleagues turned to a host of empirical observations that had been made over the past 50-plus years. When those data were plotted on a graph, the researchers found that the swimming speed of virtually every organism, from fish larvae to frogs to birds, amphibians and even whales, could be described by one of the two equations.

The same also held true, Mahadevan said, when Gazzola created complex computer models to solve the governing equations of fluid dynamics to describe how different organisms swim.

"What is particularly interesting is that all the organisms essentially reach the hydrodynamic limits of performance," he said. "Our simple theory, which doesn't distinguish in any detailed way between something like a blue whale and fish larvae, except in the parameters of how large you are, much you move and how quickly you move, can describe all this diversity. That suggests there are general principles at work here."


Source: Harvard University

Biologist reveals how whales may 'sing' for their supper

Humpback whales.
Credit: Susan Parks

Humpback whales have a trick or two when it comes to finding a quick snack at the bottom of the ocean. But how they pinpoint that meal at night, with little or no available light, remains a mystery.

Susan Parks, assistant professor of biology in the College of Arts and Sciences, in collaboration with a consortium of other researchers, has been studying these unique feeding behaviors. Her research emphasizes the importance of specific auditory cues that these mammoth creatures emit as they search the deep ocean for their prey.

Her findings are the subject of an article in the December issue of Scientific Reports ("Evidence for acoustic communication among bottom foraging humpback whales," 2014), co-authored by researchers at Moss Landing Marine Laboratories, Oregon State University, Gerry E. Studds Stellwagen Bank National Marine Sanctuary and the Whale Center of New England.

"Humpback whales are known to cooperate with others to corral prey near the surface," says Parks, who studies marine science and acoustic communication. "Recent studies suggest they may cooperate [with each other], when feeding on bottom prey, as well."

Parks was part of a collaborative multi-institutional consortium that has spent a decade monitoring humpback feeding behaviors in the Gerry E. Studds Stellwagen Bank National Marine Sanctuary, off the coast of Massachusetts. Whales were tagged with special underwater recording devices so Parks could determine how specific acoustic sounds correlated with successful seafloor feeding.

The investigation revealed that whales make "tick-tock" noises while hunting together at night in deep, pitch-black water, but are silent when hunting alone.

On the menu? Mostly sand lance -- eel-like fish known to bury themselves in the sand of the ocean floor. Parks suggests that whales' vocal sounds may help flush the sand lance out of hiding to where they're scooped up and eaten.

The clock-like sounds created by whales may also serve as a dinner bell of sorts for other nearby whales during late-night feedings.

"Hints of behavior suggest that other whales who overhear the sounds are attracted to them and may eavesdrop on other whales hunting for food," Parks adds.

Prior to joining Syracuse's faculty in 2011, Parks held various appointments at Pennsylvania State University, Cornell University and the Woods Hole Oceanographic Institution. She is the recipient of numerous honors and awards, including the Presidential Early Career Award for Scientists and Engineers, the U.S. government's highest honor for scientists and engineers.

Source:  Syracuse University

Scientists test hearing in Bristol Bay beluga whale population

Side profile of a resting beluga whale. Credit: Photo courtesy of Alaska Dept. of Fish and Game

The ocean is an increasingly industrialized space. Shipping, fishing, and recreational vessels, oil and gas exploration and other human activities all increase noise levels in the ocean and make it more difficult for marine mammals to hear and potentially diminish their range of hearing.

"Hearing is the main way marine mammals find their way around the ocean," said Aran Mooney, a biologist at Woods Hole Oceanographic Institution (WHOI). It's important to know whether and to what extent human activity is negatively impacting them.

But how can we get marine mammals living in the wild to tell us what they're able to hear?
"Same way we do it with human infants," said Mooney. "You play a sound, then you measure the brain's response to the sound."

Though Mooney makes it sound easy enough, he and his colleagues are the first to publish a study of hearing in wild marine mammals with multiple marine mammals. The paper, "Baseline Hearing Abilities and Variability in Wild Beluga Whales (Delphinapterus leucas)" was published today in The Journal of Experimental Biology.

In addition to Mooney, the research team included the paper's lead author Manuel Castellote, from the Alaska Fisheries Science Center, which is part of the National Marine Fisheries Service, and the North Gulf Oceanic Society, and their colleagues from Alaska Department of Fish and Game, Alaska SeaLife Center, and the Georgia Aquarium.

The researchers worked over a two week period in southwest Alaska during the summer of 2012, capturing and testing seven Bristol Bay beluga whales, one of six subpopulations of beluga whales in the U.S. Enabling this study are recent advances in portable field testing equipment, rugged enough for field work. To conduct their hearing tests, the team temporarily maintained the individual animals as part of physical health exams. They used suction cups to attach a small speaker to its jaw -- which in whales and dolphins conducts sound to both ears -- and placed sensors on the animal's head and back.

"The advantage is that it's really fast," said Mooney. "You can get one of these data points in about two or three minutes. A whole hearing range takes about half an hour."
In human populations, there is variability in our hearing ability: older people don't hear as well as younger people; males don't hear high frequencies as well as females. But in the tested beluga population, there was surprisingly little variation.

"The bottom line is they all hear pretty well," said Mooney. "Limitations to our study were that we had just seven animals who live in a pretty quiet environment without a lot of noise exposure. These might conserve their high-frequency better than humans, which makes sense; they need it for echolocation, and if they lose that, then they could lose of their abilities to find food and communicate."

That this kind of study has never been reported before is an indication of the challenge of capturing and testing wild marine mammals.

"It's a bit of a project. It takes a lot of people and the right environment. But we've also shown that if you have the right setup it's easy to do," said Mooney.

The team used three or four small inflatable boats and worked with Alaskan natives expert in spotting belugas, which have no dorsal fin and make only the smallest of ripples at the surface when they breathe. The guide the beluga into shallow water -- shallow enough to stand in -- until they can gently capture the 8- 12-foot animals with a hoop and net.

"Then the animal won't try and swim away, once they feel contained, they're not going to fight," said Mooney. "They will hang out there. Then you put a belly band stretcher underneath them which has little holes for the flippers. Then it goes over the belly, and that holds the animal during the test."
The team caught and measure three females and four males and essentially gave them all physicals. In addition to the hearing test, they did ultrasounds on each of the animals and collected saliva or mucous from the blow hole to look for stress hormones and took a core of the blubber to look for PCBs and other organic compounds that may build up in the fats. Together, the data gives researchers a baseline of the animals' health and a way to measure change in the population's health over time and as environmental conditions change.

While hearing in the tested animals was good, the researchers note that human-caused ocean noise is believed to be a chronic stressor and has been identified as a threat to other populations of belugas. The increase in human activities in Arctic ecosystems as a result of sea ice loss is creating a special concern about increasing ocean noise in the Arctic and its potential impacts on whales and dolphins. They note that "expanding our knowledge of beluga hearing is key to an appropriate conservation management effort."

Another driver for understanding their health and hearing now is a proposed mineral exploration and mining project in the area. The Pebble Mine project would exploit large deposits of copper, gold and molybdenum in the region. "It's not clear if it will directly affect the hearing of the belugas, but it will affect the ecology of what's up there, so the baseline health information is key," said Mooney.
The results of this hearing study may also help validate studies of hearing in belugas in captivity .
The team hopes to return to the field this summer to test a larger number of animals and attach temporary data-logging tags to learn more about their foraging, diving, and social behaviors.

Source:  Woods Hole Oceanographic Institution