MOSCOW, Sep 2, Salma Sultanova. At the end of July, one hundred black dolphins threw themselves onto the shores of the Australian beach of Chains. Despite the efforts of volunteers, half died. The rest could not be returned to the ocean — they had to be euthanized. Similar cases were noted in the summer in many places. What pushes cetaceans to suicidal behavior was analyzed by RIA Novosti.
How dolphins navigate in space
Dolphins navigate their way through the sea with a powerful underwater «sonar» — namely, sound waves that they emit in the form of clicks. Colliding with an object, the waves are reflected from it, like an echo. The faster the sound returns, the closer the prey, obstacle, or shore. Usually such echolocation works properly, however, under certain circumstances, the sound is distorted or does not come at all. For example, when an animal enters a shallow or semi-circular bay, a sandy underwater embankment or a mudflat.
In addition to sense organs and echolocation, dolphins orient themselves along the lines of the Earth's magnetic field. Magnetite crystals were found in their skulls, acting as a compass. Migration routes often pass along the magnetic lines. However, magnetic field disturbances near the coast can sometimes confuse cetaceans. 0.595622119815668″ data-crop-width=»600″ data-crop-height=»357″ data-source-sid=»rian_infographics» class=»lazyload» lazy=»1″ />
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Sounding sonar
Every year, thousands of whales and dolphins are washed ashore and killed. Isolated cases are observed throughout the world, and mass cases are most often in Western Australia, New Zealand, on the East coast of North America and off the coast of Patagonia in Chile.
Golden Bay in the northern part of New Zealand's South Island has been dubbed by the locals as the «cemetery of the dolphins». About three thousand pilot whales, black dolphins, land there every year. According to biologists from the University of Auckland, animals, swimming up to a gently sloping shore, cannot track the depth with echolocation and, without noticing it, swim further and further into shallow water. Most often — in the area of u200bu200bFarewell Spit, a narrow sandy arc at the very top of the island, forming a natural trap.
Some scientists compare this behavior with mass suicide. This was stated in an interview with The Guardian by the founder of the Center for Veterinary Wildlife Research in Truro, Vic Simpson, who, on behalf of the Zoological Society of London, conducted a post-mortem study of 26 animals that died on a beach in Cornwall in 2008.
However, according to the leading researcher of the Kamchatka branch of the Pacific Institute of Geography, Far Eastern Branch of the Russian Academy of Sciences, Doctor of Biological Sciences Alexander Burdin, there is no such thing as «suicide» in animals.
“Only a person voluntarily leaves life. Dolphins are thrown out by pure chance. The most common reason is a failure in echolocation. These animals live in a very dense and dark environment, so they rely on ultrasound. And since all types of toothed whales, especially pilot whales and killer whales, sociality is developed, a failure in one or more individuals can lead to the fact that the entire group ends up on land. This probably explains why they are thrown out or returned back to the shore after being rescued in such large numbers, «explains Burdin.
Pilot whales are strongly attached to each other and do everything together: they rest, hunt, communicate, play, travel.
«These dolphins do not have leaders. There are animals in front, but, most likely, a failure occurs for everyone at once. As a rule, — on gently sloping or sandy shores, where there are no powerful reflective surfaces. It happens that one group confidently swims towards shallow water, and the rest follow it, unaware of the threat, «the scientist continues.
The expert adds that errors in echolocation also occur through the fault of a person. So, a dolphin can lose its orientation if it gets into the zone of action of sonar — a means of detecting underwater objects. The radiation from these devices can damage the hearing of animals, since they pick up the signal not through the ear, but through the lower jaw.
«Accordingly, the rest of the pack members rush to help her,» says the scientist. «In the end, everyone ends up on land. The chain of events is different in each case, but the mechanism is the same — sociality, audibility failure, the desire to save a partner.»
According to Bourdin, the noise from the ships is unlikely to harm the dolphin: “This sound is not so strong as to bring down the echolocation of the cetacean. disorientation. There is no way to prevent this. Unfortunately, we cannot control the ocean and know in advance that a dolphin will suddenly appear in a particular place.»
Deadly dangers
“Most often, cetaceans die from diseases or the consequences of injuries caused by fishing gear. I do not exclude that sometimes, in pursuit of fish, animals do not notice how they find themselves in shallow water. This often happens, for example, with killer whales in the Sea of Okhotsk, where the tides are very high , and the water level drops up to nine or twelve meters,” Burdin explains.
It has also been noted that dolphin releases are seasonal, which may be associated with outbreaks of infections. For example, azov and white flanks are prone to fungal diseases of the skin, which are exacerbated in the spring due to changes in water temperature. However, scientists believe that if the animal has a strong immune system, it will recover. =»0.863703703703704″ data-crop-width=»600″ data-crop-height=»518″ data-source-sid=»cc_by-sa_30″ class=»lazyload» width=»1920″ height=»1658″ decoding= «async» />
Things are worse with morbillivirus, related to human measles and distemper of ungulates. Its outbreaks have repeatedly hit the Black Sea dolphins, which washed up on the shore in dozens.
For them, this infection is very dangerous. So, in 2021, American and Canadian scientists discovered a new lethal strain of cetacean morbillivirus by studying the remains of a Malaysian dolphin, which a couple of years earlier had washed up on the coast of Maui (Hawaii). Outwardly, everything looked like the death of a healthy animal, but the internal organs were affected, and blood was found in the cerebrospinal fluid. At autopsy, researchers found traces of an unknown strain of morbillivirus in the cerebellum, lungs, kidneys, and lymph nodes. This is a bad sign, since new highly pathogenic strains often cause outbreaks of infections. They killed 250 dolphins in Australia and Brazil.
Last year, a wave of mass deaths swept along the Crimean coast of the Black Sea. Volunteers stood in the water day and night, trying to save bottlenose dolphins, common dolphins and azovok (porpoises). The infection was the culprit. Experts have calculated that no more than ten percent of dolphins wash ashore, most of the infected animals die in the sea.
Another threat is neurotoxin poisoning. Since the beginning of June, dead dolphins and sea lions have been found all over the southern coast of California. Scientists claim that this is due to the spread of Pseudo-nitzschia microalgae, which produce domoic acid, which acts as a neurotoxin. Last year, it killed dozens of marine mammals in the area. However, according to Santa Barbara Marine Mammal Rescue co-founder Sam Dover, the current crisis is unprecedented. But abrupt changes in weather and chemical conditions in the ocean provoke its rapid growth, and hence the production of pigment. It can accumulate in organisms at the bottom of the food chain and poison those who feed on them.
shore
This summer, 55 black dolphins found themselves on the shore of the Isle of Lewis (Scotland). Only one was saved. The incident was recognized as the largest in the last 70 years in this region.
The dolphin has practically no chance of returning from shallow water to depth. According to Alexander Burdin, the critical moment is drying. After it, it is extremely difficult to bring the cetacean to his senses.
«Dolphins do not deliberately throw themselves ashore. First they swim in shallow water, and then the waves push them to land. The ebb tide prevents them from going back into the sea. The water level drops significantly, and the animal finds itself on bare sand. This immobilizes him. To push the dolphin back, you have to wait for the tide. At this point, the sun begins to dry the skin. If you do not start pouring it, the dolphin may die from overheating.»
Grinds are large mammals, up to seven meters in length, weighing about a ton. Under water, such dimensions are not a problem, but on the shore, a heavy animal begins to slowly die. Blood circulation stops, the body is gradually poisoned by toxins. Therefore, time is of the essence. width=»600″ data-crop-height=»400″ data-source-sid=»ap_photo» class=»lazyload» width=»1920″ height=»1280″ decoding=»async» />
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Teams of volunteers — biologists, employees of various organizations, local residents — are involved in the rescue. When the water rises, the dolphins are pushed by hand to special boats and tied to the side to be taken to a safe depth.
Cetacean strikes cannot be predicted, much less prevented, experts warn. After all, these animals spend all the time under water, which makes it very difficult to study their behavior.