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It seems that one of the most frightened ocean predators may be scared.
A new study conducted by the Monterey Bay Aquarium and published Tuesday in Nature revealed that great white sharks were leaving their "preferred hunting ground" when orcas – also known as killer whales – they entered. In fact, the researchers found that sharks would not return to these areas for about a year, even if the killer whales did not stay that long.
To reach this conclusion, the researchers "documented four encounters between the main predators of southeastern Farallon Island in the Grand Farallones National Marine Sanctuary off San Francisco, California," according to the statement. press published by the Monterey Bay Aquarium. The scientists then "analyzed the interactions using data from 165 white sharks tagged between 2006 and 2013 and compiled 27 years of records of seals, killer whales and Farallone sharks".
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Specifically, researchers determined when sharks and killer whales were present in Farallon Islands by comparing shark tag data with "field observations of killer whale observations".
"This has shown the result on the rare cases where predators have met," according to the study.
"Robust data sources" helped scientists "conclusively show how white sharks retreat from the area when killer whales manifest themselves," said Jim Tietz, co-author of the study, in a statement. communicated online.
The sharks fled the island when the orcs arrived – and did not return until the next season – in all cases studied. The electronic tag data even showed that all the great white sharks had left the area only minutes after the arrival of the killer whales. This was true even when killer whales were present less than an hour.
"It turns out that these risk effects are very important even for large predators such as the white shark – powerful enough to redirect their hunting activities to less desirable but safer areas."
"On average, we document about 40 elephant seal predation events by white sharks in the southeast of Farallon Island," said Scot Anderson, scientist at the Monterey Bay Aquarium. in a statement. "After the killer whales have come out, we do not see a single shark anymore and there are no more victims."
"They are huge white sharks, some are over 18 feet and are usually the law here," Anderson said.
It is unclear why exactly sharks leave. The researchers suspect that this could be due to the fact that sharks are prey to killer whales, or perhaps also because they are bullied for food and are eventually hunted.
Sharks that sail out of the region have an indirect benefit for the elephant seals – which are often the favorite food of sharks and killer whales – Farallones. The researchers found that there were "four to seven times fewer predation events on elephant seals over the years that white sharks have left," according to the study.
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"In general, we do not think that fear and risk aversion can play a role in hunting large predators and its influence on ocean ecosystems," added Salvador Jorgensen, lead author of the 39; study. "It turns out that these effects of risk are very powerful, even for large predators like white sharks, powerful enough to redirect their hunting activities to less desirable but safer areas."
Jorgensen explained that the study is important because it is one of the few to "demonstrate that food chains are not always linear", especially in the oceans. Interactions between predators are more difficult to document and analyze because of their low frequency.
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