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An extreme event has also years later, still negative consequences

in order To track prey, to send dolphins with their front head, high-frequency sound pulses. Again and again they'll send out clicking sounds. This will be reflected then about from the swim bladder of a fish, make use of the marine hunters of the Information immediately. "Even when visibility is poor dolphins can be found using the Echo-location yet to successfully food," says Michael Krützen of the University of Zurich, the researched for more than two decades, the behavior and the genetics of the smart marine mammals, in Shark Bay off the West Australian coast.

But now the scientists are Worried about the living there, as yet, quite a large Population of the so-called Indo-Pacific, Large bottlenose Dolphin. Because his co-worker Sonja, Wild has shown in her Dissertation that in the past few years, the survival rate of the animals, as well as the number of calves has diminished considerably. This is the Zurich-based team of researchers reported, together with colleagues from Australia, England and the USA in the current issue of the journal "Current Biology".

Due to the marine heat wave during the Australian summer at the end of 2010 and beginning of 2011, the dolphins find there today less food compared to the past. "We have for the first time, can show that such an extreme event has also mammals years later, still negative consequences for the Navy," says Krützen. Dubious that is to be expected as a result of climate change with such a devastating abnormalities in the future even more frequently.

Mass death of fish

But what had happened? Due to the weather phenomenon La Niña, the water is not heated at the time, in the Shark Bay so strong that it was during more than two months two to four degrees Celsius above the otherwise at this time, the usual average temperature. This led to the fact that in the sea, more than a third of the seagrass Bay meadows damaged. The green plant carpets are extremely important for the whole Ecosystem, because, among other things, a lot of fish grow and their food.

"such A catastrophic loss of Habitat has explained the consequences for the smallest organisms to the Top predators that are at the top of the food chain," Krützen. The damage to the seagrass die-free of a myriad of invertebrates and schools of fish led the mass. The water was so warm that it had a murky coloration.

in 1991, the legendary Shark Bay due to its natural beauty, biological diversity and fascinating Ecology, and also because of their more than 3.5 billion years old, by living organisms resulting deposition of the rocks, a Unesco world heritage site. In addition to dolphins, manatees swimming around, among other things. The enormous species richness is mainly due to the typical sea grass meadows back, no longer able to regenerate after the heat wave eight years ago until now.

Dolphin experts from Zurich to observe the Population for four months of the year. Photo: Simon Allen/Dolphin Innovation Project

From 2007 to 2017 under the group Krützen sought a total of more than 1000 dolphins in a 1500-square-kilometre area of the Bay, and documented them all. "We are able to distinguish individuals on the basis of their fin and body colouration on the page, as both an individual fingerprint," says the Zurich-based researchers. In addition, they had many animals, including genetic data, so that they knew exactly who was related to whom.

Because of the dolphins in Shark Bay are stationary, seems to be the lack of fish to have especially weaker animals, such as pregnant or lactating females and their young no harm. The researchers found that after the heat wave, the survival rate depending on the Delfin group of either six or twelve per cent had fallen. In addition, the reproductive rate of females was in General, after the heat wave is much smaller.

search for food in the deep

The special feature of Shark Bay is that there are two types of bottlenose dolphins: The a not use a sea sponge as a tool for hunting, the other. Who are carriers of the Sponge, comes out clearly compared to the other better with the changed Situation. Because their hunting grounds are meadows up to twelve meters in deeper areas without the green seaweed.

With a sea sponge as a protection in front of the muzzle you plough through the sea floor. In this way, it can't hurt to stones and shells. A in the Sand hidden platform is startled fish or a Moray eel, throws away the Dolphin the sponge and grab the loot. About 150 of more than 3,000 dolphins in Shark Bay use this clever hunting technique. "You're lucky that your main source of food was not affected by the heat wave," says Krützen.

Every year, during four months, the Dolphin experts from Zurich to observe, together with colleagues from abroad every day between three and ten groups. "We look at what you do, who is with whom on-the-go, and whether the females have calves," explains the researcher. You would almost know everyone and have you also photos in the extensive database.

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explore obtain a DNA sample from the animal is shot from another boat with a biopsy gun and an arrow directly into the fatty tissue just under his dorsal fin. Then the arrow falls out and floats in the water, so that the genetic Material can be collected and later analyzed in the laboratory.

"we are watching the dolphins with drones," says Michael Krützen. As a result, your fast interactions in the group, you can even better track. Even the researchers go never into the water. "Finally, the Bay Shark Bay is," he adds. And the approximately four-metre-long Hammer and tiger sharks come regularly to take you to the boat. (Editorial Tamedia)

Created: 01.04.2019, 17:36 PM

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