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The zifidos, also known as Cuvier’s calves, are incredible divers, but the sounds they emit to ecolocalize left them exposed to a dangerous predator: the killer whales. New research shows how these groups of whales have managed to coordinate their deep dives to do so in stealth and thus get rid of their predators.
These medium-sized whales, of which there are more than 20 different species, use echolocation to find their prey, a strategy that has the unfortunate side effect of alerting the orcas nearby. Killer whales, as good predators that they are, are more than happy to take full advantage of this situation.
It is understandable that Cuvier’s calves have developed a natural fear of killer whales. An article published yesterday in Scientific Reports shows how this fear has led to an effective but complex strategy that essentially makes these whales invisible to killer whales: really deep dives to feed and then a quiet and unpredictable ascent.
As their coordinated dives begin towards the bottom of the ocean, the calves enter stealth mode, ceasing to emit sounds to echolocate. Once they are at the right depth, they give free rein to their echolocation skills, and spend more than an hour hunting sea animals. When they have finished, they re-activate the stealth mode during their slow and synchronized ascent, to end up emerging in a seemingly random location.
One of the main motivations of this study, in which marine biologists Natacha Aguilar de Soto of the University of La Laguna and Mark Johnson of the University of St. Andrews participated, was to get a better idea of how underwater sonars could be affecting to these whales, which are usually stranded on the beaches in large numbers.
“When Cuvier’s calves began to be stranded after the naval sonar exercises, we knew very little about their behaviour. But when we started to learn about them, we found them more strangers, ”Johnson told Gizmodo. “Compared to other whales that also dive deep, such as sperm whales, Cuvier’s whales dive in a way that seems to make no sense of energy. We wanted to understand what made them behave like this and see if that made sense of their strong reactions to sonar. ”
The problem is that Cuvier’s whales are exceptionally difficult to study, since they live in deep waters away from the coast in waters and are difficult to detect in the open sea. The researchers had to find specimens in places relatively close to the coast, and this led them to the deep waters of the Canary Islands, the Azores and the Ligurian coast.
The next challenge was to find a way to track these animals the size of an elephant, who spend more than 90% of their time underwater.
“To do that, we design small electronic tags that record their sounds and movements and stay attached with suction cups,” Johnson said. “The labels only hold one day but record an immense amount of data on their behaviour.”
In fact, these tags that later recovered allowed the team to track the movements of the whales in detail, collecting data such as the inclination, depth and duration of their dives and even the sounds they made. In total, the researchers studied the behaviour of 26 specimens, of which 14 were Blainville’s snout whales and 12 were Cuvier’s whales.
The data showed that the whales make their fully coordinated dives to each other, up to almost a kilometer deep and spend more than 45 minutes underwater ( that’s a lot of time holding your breath!).
The whales stopped emitting echolocation sounds when they were in shallow waters, where they are more vulnerable to killer whale attacks . They only resumed them when they were almost half a kilometer of immersion , and then separated and hunted independently.
In addition to using echolocation to detect prey, it also allowed whales to find themselves in the dark waters .
The whales also made a “silent ascent coordinated in an unpredictable direction,” the authors of the paper wrote . Appearing suddenly and at a point far from the place where they had emitted their last sound, the calves made it much harder for the killer whales to track them.
When asking Johnson if this behaviour could be due to something else, he said: ” Many behaviours serve more than one purpose, so we cannot say that this diving strategy is only to prevent predation.” That said, ” the other proposed explanations make no sense, ” he added. Other scientists “have explored whether est and long ascent could help ballenatos avoid problems by decompression, as happens to divers , or save energy in some way , but have found no explanation that fits, ” Johnson said.
However, this survival tactic has a cost. The researchers calculated that these dives at such depths , reduce the time they can spend looking for food up to 35% , although at the same time, their immersion tactics “reduces the risk of killer whale interception,” the authors wrote d the study. Therefore, this evolutionary strategy must have arisen from the threat of killer whales , the researchers say.
Regarding how naval sonar could be affecting these whales , Johnson said sonar could have a negative influence on their behaviour.
“Cuvier’s calves don’t want to take a risk, so any unusual sound that may come from a predator can trigger strong evasive behaviour,” Johnson told Gizmodo. “This is a strategy that has worked for millions of years, but the invention of sonar has brought new sounds into the water that the calves cannot discriminate against that of predators.”
Unfortunately, is another sign that human activities are affecting the nature and hurting some of the most fascinating creatures that inhabit our planet.
Watch the Youtube video below …
Source: ES Gizmodo