For several decades dolphins and fishermen have been hunting together on the beaches of southern Brazil. A new international study reveals how this cooperation contributes to the marine mammals' chances of survival and what we must do so that it does not disappear from the world
Two groups of predators meet; One swims in the sea and the other stands on land: dolphins and humans. The land group enters the shallow water and waits for a sign of an assault. Then, the dolphins dive and the skilled fishermen cast the heavy fishing nets in front of them, and in no time the nets - and jaws - are filled with fluttering mullets.
This scene is taken from the beach of the city of Laguna (Laguna) in southern Brazil - where the cooperation between the local fishermen and the dolphins is part of the local culture. But while the humans are quick to locate fish by the marine predators - and the human interest in this cooperation is quite clear - for many years the dolphin's profit in the described relationship remained undeciphered. Why do untamed dolphins cooperate with humans?
A new international study Reveals the dolphins' interest in coordinated hunting: The researchers found that human-dolphin cooperation contributes to the survival chances of these marine mammals. In addition, the researchers discovered that the coordinated hunt is fading and disappearing, mainly due to the dwindling of the mullet fish in the area. Will one of the fruitful collaborations - and the last - between humans and wild animals disappear completely and be left only in the pages of history?
animals with IQ High
The marine mammal described in the previous paragraphs is The common dolphin (Tursiops truncates), a common species that also swims on the shores of our country - and which is characterized by high intelligence and adaptability. Today, dolphins and humans cooperate in Brazil, in India, in Myanmar and in Mauritania.
"In some characteristics that indicate intelligence in animals, such as the size of the brain in relation to the body, the learning abilities and the complexity of the social structures - the dolphins are second only to humans," explains Dr. Aviad Shainin, director of the super carnivore field at the Maurice Kahn Marine Research Station of the School of Marine Sciences at the University Haifa and the director of the Dolphin and Sea Center of Delphis Association. "Here in Israel, the dolphins, and especially dolphins nursing their pups - have realized that the trawlers that drag a net behind them produce a collection of fish that is easy to hunt; This is how they use the vessels to make it easier for them to obtain food."
Due to the dolphin being a particularly smart animal that works for itself, researchers believed that the marine mammal benefits greatly from cooperation with the fishermen - but only the new study attacks this claim and reveals the variety of direct and indirect profits that the dolphins receive.
The researchers used documentation, some of which spanned 15 years, and observations that included the use of drones, underwater cameras, sonars, hydrophones (marine microphones) and GPS bracelets (which were worn by the fishermen).
interests of dolphins
The scientists discovered that dolphins who participate in the joint hunt have a 13 percent higher chance of survival than their brothers who did not get the "trick". This impressive figure has direct and indirect reasons.
The first and direct way in which the dolphins benefit from the cooperation with the fishermen is - you guessed it - guaranteed meals: when the dolphins attack from one side and the fishermen throw nets from the other side - the fish have nowhere to run, so it is easier for both predators to hunt them (and the study indeed found that the fishermen also get more prey when they cooperate with the dolphins).
The researchers found 3 signs that they say indicate that the dolphins are indeed benefiting from the cooperation with the humans: First, the fishermen indicate that they feel the tugs in the nets when the dolphins remove fish caught in them. Second, according to the researchers, the dolphins' long diving time indicates active hunting. Third, through underwater sound recordings, the researchers discovered that the sonar mechanism by which dolphins locate their prey goes into "hunting mode". "The sonar is used by the dolphins when they dive into dark areas: they send a sound wave and receive a return with which they build an image in their head," explains Sheinin. "Often the mullet fish, which they eat, swim in murky water, so the sonar gives them an advantage in catching them." According to Shainin, the "hunting mode" in question is activated when the dolphins approach their prey - then they raise the frequency of the waves to get a more accurate return.
In addition to securing their meals, the researchers found an indirect reason for the dolphins' benefit from cooperation with humans: the coordinated hunting prevents these mammals from foraging in other areas of the southern Brazilian coast, where fishermen use fishing methods that are dangerous to them. "The main cause of death for dolphins near the coast, even in Israel, is entanglement in fishing equipment," explains Sheinin. "The standing nets, which the fishermen throw into the water and wait for the fish to pass by and get caught in it - sometimes they also catch dolphins who recognize a fish in the net, get entangled in it and drown."
And if you were wondering about the way humans use the dolphins' abilities to leverage human fishing, the researchers looked into this aspect as well: the study found that the presence of dolphins in the interaction zones increases the more mullet are near the shore, and thus the fishermen recognize that they should enter the water. The dolphins "herd" the fish towards the fishermen, who throw their nets in. In this way, the dolphins improve the fishermen's chances of success by 17 times and the scope of their prey by 4 times. By the way, the fishermen must react in time and reach the exact place where the dolphins are in order to gain optimal success, but they do not always do so - but only in about 50 percent of the cases .
Tracking for years - maybe the last few years
And now that you've imagined dolphins and humans together, shoulder to fin, here's the less-than-harmonious side of the study: this mutual human-dolphin relationship is in danger. According to the researchers, this is a phenomenon in decline, which will disappear in the coming decades. The main reason for this is the dwindling of mullet fish in the southern region of Brazil overfishing - A situation where the amount of fish caught is greater than the regeneration capacity of the natural population. This decline is also happening in the rest of the world, and the common fishing culture has already disappeared from places where it existed; For example from Australia, China, Eastern Russia, Canada and various European countries.
therefore, The researchers recommend on two measures that will help preserve the cooperation in question: managing the fishing industry in the area in a more sustainable way (for example, setting seasonal fishing quotas and enforcement against illegal fishing) that will allow for the recovery of the mullet population, and granting economic incentives to the local fishermen who are skilled in cooperating with the dolphins - so that they do not will move to other and harmful fishing methods. In addition, the researchers also emphasize the uniqueness of this relationship in the 21st century - where man is hardly ever in mutual interaction with nature. "We are part of nature - and influence it perhaps more than all the other elements," says Sheinin. "And therefore we have a responsibility towards him - from which we must not avoid", he concludes.
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