Tuesday, June 15, 2021, 7:38 p.m. – Lead author of the study said more than 70% of the world’s sharks have perished, with an even greater death toll for those who occupied the ocean rather than coastal waters.
The discovery of a massive shark disappearance millions of years ago has left scientists scratching their heads looking for the cause.
A recent study conducted by scientists at Yale University and College of the Atlantic found significant shark mortality around 19 million years ago. This happened at a time in Earth’s history when the population of sharks navigating the world’s oceans was more than 10 times what it is now, according to a press release from the University of Yale.
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But researchers still don’t know why.
“We stumbled upon this extinction almost by accident,” Elizabeth Sibert, Hutchinson postdoctoral fellow in the Department of Earth and Planetary Sciences at Yale and the Yale Institute for Biospheric Studies, said in the statement.
Sibert, the lead author of the new study published in the journal Science, said more than 70 percent of the world’s sharks have perished, with an even greater death toll for those who occupied the ocean rather than coastal waters.
The toll was double the level of eradication suffered by sharks during the Cretaceous-Paleogene mass extinction 66 million years ago, which wiped out three-quarters of all plant and animal species on Earth.
“I’m studying microfossil fish teeth and shark scales in deep sea sediments, and we decided to generate an 85 million year record of fish and shark abundance, just to get a feel for the normal variability of this long-term population, ”said Sibert.
“What we found, however, was this sudden drop in shark abundance about 19 million years ago, and we knew we needed to do more research.”
NO KNOWN DISASTER OR DISASTER
The conundrum surrounding the cause is reinforced by the fact that there is no known climate catastrophe or ecosystem disturbance that took place at the time of the shark populations’ sharp decline.
“This interval is not known for any major change in Earth’s history,” Sibert said, adding, “but it has completely transformed the nature of what it means to be a predator living in the open sea”.
Co-author Leah Rubin, a new doctoral student at the College of Environmental Sciences and Forestry at State University of New York, said in the statement that the current state of shark population decline is ” certainly worrying ”.
“This article helps put those declines in the context of shark populations over the past 40 million years,” Rubin said. “This background is a vital first step in understanding what repercussions the dramatic declines of these major marine predators could follow in modern times.”
Earlier discoveries of extinction events have given rise to dozens of new research to uncover the origins of death and whether this indicates greater, previously unknown distress in global ecosystems, the scientists noted.
As an example, further research could verify whether the disappearance led the remaining shark populations to adjust their habitat desires in order to avoid the ocean, Sibert and Rubin said. Additional research could also help explain why shark populations did not recover after death around 19 million years ago.
(Courtesy: Wikipedia / CC BY 3.0)
“Shark populations have been depleted in recent decades due to overfishing and other anthropogenic stressors. However, the long-term impacts of such changes in the abundance and diversity of marine predators are poorly limited. We present evidence of a previously unknown major extinction event in sharks that occurred in the early Miocene, (approximately) 19 million years ago, ”the authors noted in the study.
Thumbnail courtesy of Sharkdiver68 / Wikipedia
Nathan Howes can be followed on Twitter: @HowesNathan.