Strange animal behavior: find sharks "slaughtered" by swordfish

Strange animal behavior: find sharks "slaughtered" by swordfish
Strange animal behavior: find sharks "slaughtered" by swordfish
Anonim

The corpse washed ashore last week near Benidorm, eastern Spain, is another example of an increasingly widespread phenomenon that has baffled scientists.

Last week, the appearance of the blue shark forced the evacuation of a beach in Benidorm, in eastern Spain. A shark about two meters long and weighing about 60 kilograms got disoriented and ended up in an area where there were many swimmers. Rescuers from the Oceanogràfic of Valencia managed to catch the shark, after being tested it was found healthy and returned to the sea.

On Saturday, August 21, the same specimen was found in the municipality of El Campello, 30 kilometers south, where it was caught dead the next day. According to a necropsy performed by Jaime Penades, a researcher in the Marine Zoology Department of the University of Valencia, the cause of death appears to have been a small wound near the eyelid, which was already visible in videos taken a few days earlier by the local maritime police; a wound that is compatible with a swordfish attack. Until recently, this type of aggression was a complete mystery to scientists, but a series of cases prompted research into the relationship between these two marine animals.

The first scientifically documented case of a deadly swordfish attack on a shark occurred in Valencia in 2016. The specimen was found dying on a nearby beach. Subsequent analyzes revealed an 18-centimeter fragment of a swordfish's blade that had dug into her brain. "The sword completely pierced and split the shark's brain in two," explains Penades, co-author of the study.

"Aggressive interaction between juvenile swordfish and blue sharks in the Western Mediterranean is widespread."

"At the time, we were amazed. We didn't expect to find anything like this." This first recorded case has been a wake-up call for the scientific community to see if there are any other signs of this type of attack. Since then, similar cases have been recorded in Italy and Libya.

By June 2019, Penades' team had managed to document five more attacks. Since then, new cases have been discovered and will be documented shortly. All cases of killing sharks by swordfish follow the same pattern.

“The blows are to the head, so the swordfish works with intent,” says Penades. "This is not a random attack. It is also very accurate because it hits the eyes or the brain, which are vital organs of sharks."

Due to the limited data available, it is difficult to tell if attacks are common to other areas of the body. Researchers are also unsure if this is active swordfish aggression or self-defense, although Penades suspects that due to the smaller size of the swordfish, they are most likely trying to defend themselves.

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The main obstacle to finding new examples of such attacks is that dead sharks do not swim. "It's very difficult for a shark to get broke," says Penades. "Dolphins are easier because they swim, but sharks usually drown." In addition, the tests required to locate the swordfish fragments are not routinely performed.

“The blows are to the head, so the swordfish is acting with intent,” says Penades. "This is not a random attack. It is also very accurate because it hits the eyes or the brain, which are vital structures."

Due to the limited data available, it is difficult to tell if attacks are common to other areas of the body. Researchers are also unsure if this is active swordfish aggression or self-defense, although Penades suspects that due to the smaller size of the swordfish, they are most likely trying to defend themselves.

The main obstacle to finding new examples of such attacks is that sharks do not swim. "It's very difficult for a shark to get broke," says Penades. "Dolphins are easier because they swim, but sharks usually drown." In addition, the analyzes required to locate swordfish blade fragments are not routinely performed. "Usually, with necropsy, the cerebrospinal fluid is removed, but the skull is not opened and there is no full autopsy," says Penades.

Fortunately for the researchers, the Valencian Community Beach Network has records of specimens found in the waters of the region, allowing them to analyze their physical condition upon arrival. “We were able to look back and see sharks with similar injuries - ones that we didn't know where they came from,” says Penades. With the help of the Oceanogràfic Foundation, they were able to perform several CT scans and X-rays. “We found a shark that had a sword fragment inside its skull, but it had already healed; it was an animal that survived the attack of a swordfish,” he says.

The reason this type of aggression is being detected more and more often may be because until now no one has paid attention to it, as Penades notes. However, he also believes that something, such as global warming, could be the cause of the attacks, although he admits that there is currently no evidence to support this.

“We are all very quick to mention climate change these days, which is certainly a reality,” he says. "But in this case, I think this is most likely due to the fact that we did not take it into account as an opportunity; we did not even check it."

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