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An extinction event around 19 million years ago decimated shark populations by up to 90%, researchers say.
In an article published Thursday in Science magazine, oceanographer and paleontologist Elizabeth Sibert and Leah Rubin of Yale University, then a student at the College of the Atlantic at Bar Harbor, report, Maine, wrote that shark populations have still not recovered from the abrupt death.
LARGE WHITE SHARK POPULATION ALONG CALIFORNIAN COAST IS BOOMING
By studying shark teeth and other marine microfossils buried in sediments of the deep-sea Pacific, the two reports reportedly found that current shark diversity was only a “small remnant of a much wider range of forms” created by the Extinctions in the Miocene were eliminated.
Sibert emailed Fox News on Saturday that she and Rubin discovered the event “completely by accident”.
“I study microfossil fish teeth and shark scales – a special niche group of microfossils in the already small field of micropalaeontology – so not much is known about them,” she said. “We decided to make a long record of fish and shark fossil abundance going back many millions of years in the same location just to see what the normal background variability is. … We found that the ratio of fish teeth to shark rubber (teeth) in the sediments was constant for over 40 million years (from ~ 60 million years ago to 19 million years ago), with about 1 shark fossil for every 5 fish fossils.
“But 19 million years ago that changed suddenly and dramatically, and that ratio dropped to about one shark fossil for every 100 fish teeth or more,” said Sibert. “Nineteen million years ago wasn’t really known in geological history as a time of rapid environmental change – so we didn’t expect any change in the vertebrate community, let alone a huge shark extinction!”
However, its cause remains in the dark, notes the paper, since “there are no known climatic and / or environmental causes for this extinction”.
“Modern shark shapes began to diversify within two to five million years of extinction, but they are only a small fraction of what sharks once were,” the researchers found.
The study also posits that the early Miocene was a time of “rapid, transformative change for open ocean ecosystems”.
“Like most research, this first paper poses more questions than it can answer, and we plan to explore the breadth of data supply from denticles through a variety of lenses, from hydrodynamics to ecology,” Rubin said in a quote to Fox News.
The results of Sibert and Rubin – who are now PhD students at the State University of New York College of Environmental Science and Forestry – confirm those of an earlier study using the same dataset.
In 2018, a separate group of scientists analyzing shark teeth from fossil debris reported in the journal Current Biology that the asteroid that wiped out dinosaurs 66 million years ago also killed up to 34% of prehistoric shark species.
However, sharks were able to survive millions of years later without major disturbance.
While the numbers of pelagic predators have declined in recent years, largely due to overfishing and other anthropogenic stressors such as climate change, recent reports from both Pacific and Atlantic waters show that great white shark populations are booming.
Although the 2021 “shark season” is just beginning, more than 100 young whites were recently tagged off the coast of Southern California and a study did published in the journal Biological Conservation found that between 2011 and 2018, the number of white whites in Pacific waters increased significantly.
The report’s authors also suggested that there had been “a similar regional increase in great white shark numbers” in the US Exclusive economic zone of the Northwest Atlantic “, citing a 2014 study that predicts an optimistic outlook for the great white shark recovery in the Atlantic.
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Still, a January report in the journal Nature found that the global abundance of sharks and rays has decreased by 71% since 1970.
According to Smithsonian’s Ocean Portal, there are more than 500 species of shark, with an estimated 100 million deaths from fishing each year.