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Why Do Whales and Dolphins Strand?

Animals
Rescuers assist beached long-fin pilot whales at Hamelin Bay, Australia on March 23, 2009. Tony Ashby / AFP / Getty Images

Alexander Freund

Pilot whales, sperm whales, beaked whales and deep-sea dolphins are the marine mammals most commonly involved in mass strandings. Baleen whales, on the other hand, a group to which all big whales except the sperm whale belong, strand very rarely.


If these mammals become stranded, they can dry out, overheat, suffocate or suffer severe inner injuries because of their enormous dead weight.

Individual strandings have been observed at many locations, while most mass strandings have been registered in Western Australia, New Zealand (with up to 300 stranded whales annually), and on the east coast of North America and Patagonia (Chile). Occasionally, however, there are also mass strandings in the North Sea.

How Do Whales and Dolphins Navigate?

Like migratory birds, some whale species travel great distances every year. In winter, whales migrate from the cold northern seas to warmer waters in the south, and whales from southern waters move to the north in the same season. Months later, they then begin to travel back home.

The smaller toothed whales, such as dolphins, have a powerful underwater sonar. They orient themselves on their journeys by emitting sound waves in the form of clicking noises. When these sound waves collide with an object, they are reflected back as echoes to the animals' ears, which in the case of whales are shielded from the skull in foam-filled chambers inside the body to enable spatial hearing. The faster the sound returns, the closer the prey, an obstacle or the coast.

However, in the case of the large baleen whales, which have horn plates (baleen) instead of teeth in their upper jaws for filtering krill, animal plankton and small fish from the water, this underwater sonar is not very highly developed.

This echolocation works very well as a rule. However, sound reflection does not function reliably in certain circumstances, particularly when there are shallow or semicircular bays, sandy underwater embankments or silt banks. These types of coasts and obstacles do not produce an unambiguous echo from any particular direction, so the warning system fails.

What Influence Does the Earth's Magnetic Field Have?

Whales such as the pilot whale do not use just underwater sonar to orient themselves, but — again, like migratory birds — seem to rely on the lines of the earth's magnetic field, as their migration routes often run parallel to those lines. The slight fluctuations of the earth's magnetic field appear to function like a kind of map.

Magnetite crystals have been found in the skulls of these animals. The whales could be confused by disturbances of the geomagnetic field near the coast. Magnetic fields running perpendicular to the mainland are also thought to play a role in mass strandings of whales in certain coastal regions.

Every few years, solar storms and sunspots that occur amid heightened activity on the sun's surface also cause fairly large changes in the Earth's magnetic field. It is at such times that sperm whales, for example, which also use geomagnetism as a natural navigation system, get lost and become stranded in the North Sea.

Why Do Whales and Dolphins Become Stranded?

Navigational errors are thus believed to be the main cause of whale strandings, but all the reasons have not yet been conclusively investigated.

One of them is certainly the social behavior of many whale species, which travel in groups, so-called pods, and are guided by a leader. For example, in the case of sperm whales, a male leads the way from the Arctic Ocean back into warmer waters. By contrast, when orcas are on their travels, a mother or grandmother leads the group.

If leaders lose their orientation, perhaps because they are confused or because parasites have attacked their ears, rendering them incapable of hearing the echoes of the clicking sounds that have been sent, the accompanying animals will follow them in the wrong direction. If a leader is stuck in shallow waters, the rest of the group stays with it, even if this means their certain doom.

Sometimes, as has been observed, for example, with orcas on the South African coast, this group cohesion can go so far that whales who have already been saved after a mass stranding return to the beach if another stranded whale calls for help.

But strandings can also have other natural causes. Sometimes, smaller dolphins become beached because they have taken refuge from orcas and other predators in shallower waters or because they have ventured too far into shallow areas when hunting shoals of fish.

Occasionally, individual animals are also washed ashore dead after being previously injured by collisions with ships, fishing nets or shark attacks or becoming ill from infections or parasite infestation.

Which Human Influences Exacerbate the Situation?

In addition to natural factors, man-made underwater noise from ships, icebreakers, drilling platforms or military sonar equipment can also massively impair the orientation and communication of marine mammals. They flee the strong sound waves in a state of confusion. And since the density of water is much higher than that of air, sound propagates underwater about five times faster than in the air.

Military sonar operations employing very loud sounds have particularly drastic effects. After NATO maneuvers, for example, beaked whales have washed up dead on the coasts of Cyprus, the Canary Islands and the Bahamas. The sonars, which are louder than 200 decibels, triggered the formation of gas bubbles in the blood vessels and organs of marine mammals (as happens with diving sickness), obstructing the blood supply and leading to their death.

How Can You Help Stranded Whales and Dolphins?

When a whale stranding is discovered, there is usually not much time left. Teams of helpers can do little more than try to cool the stranded animals, keep them moist and combine forces to get the heavy animals back into the sea as quickly and gently as possible.

In some countries, hotlines have been set up so that as many helpers as possible can be mobilized quickly. For many exhausted animals, however, even these immediate measures often come too late.

Reposted with permission from Deutsche Welle.

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A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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