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Researchers not likely to find cause of Wrightsville Beach shark’s death

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Sometime last fall, a great white shark in the Atlantic Ocean took a tremendous bite out of a 50-pound black drum, swallowing nearly two-thirds of the 4-foot-long fish.

It was the last meal of the shark that on Dec. 7 would wash ashore on Wrightsville Beach, a University of North Carolina Wilmington biology professor studying the animal said this week.

And while it looks likely that scientists will never be able to determine exactly how the female shark died, she is nonetheless revealing new details about her mysterious species and will help researchers across the country learn more about the species that the World Wildlife Foundation lists as vulnerable.

“We learned that black drum is on the menu,” said Thomas Lankford, associate professor at the school’s biology and marine biology department. “We know very little about the food habits of white sharks in the western Atlantic. What are their common prey? What sorts of actions we take as humans might have consequences for the shark. Knowing that black drum is a prey item for our local white sharks is important to know.”

Supplied photo courtesy of UNCW marine biology department. A UNCW student helps document the bite marks on the great white shark that washed ashore on Wrightsville Beach on Dec. 7, 2015. Recent tests show that the bite marks were a result of sharks scavenging the carcass after it had already died and didn’t play a role in the animal’s still unknown death.
Supplied photo courtesy of UNCW marine biology department.
A UNCW student helps document the bite marks on the great white shark that washed ashore on Wrightsville Beach on Dec. 7, 2015. Recent tests show that the bite marks were a result of sharks scavenging the carcass after it had already died and didn’t play a role in the animal’s still unknown death.

The latest tests were returned in early May, where histopathologies conducted on tissue from bite wounds found that the bite wounds on the shark occurred after its death, eliminating questions of whether the bites killed the animal.

“This test showed that there’s no smoking gun,” Lankford said on the shark’s demise.

Led by UNCW biology and marine biology research associate William McLellan and Lankford, a team of UNCW undergraduate and graduate students conducted a series of tests on the animal, beginning with the Dec. 8, 2015, necropsy that drew more than 100 spectators.

Some remaining mysteries include the female shark’s age and where it died. However, researchers determined that the shark had not yet reached sexual maturity, and their estimates put the animal’s age at between 15 and 20 years old, said Lankford, adding that recent research put the white shark’s average lifespan at 70 years. It weighed 688 pounds and measured 10.9 feet long.

In searching the animal’s stomach, the researchers found two unique bones that are present in the ears of fish, identifying them as from the black drum. Researchers also found the remnants of 141 fisheye lenses, with the largest being those of the black drum. The wounds found on the inside of the animal’s esophagus likely came from the spiney bones of the black drum.

The shark died seven to eight days before it washed ashore, but Lankford said they don’t know where the shark was, though the UNCW team did have an idea on how to research the question.

By working with oceanographers to plot the wind and currents of that period, they may be able to get a general idea of which direction the shark floated from.

UNCW’s researchers made other interesting discoveries in their dissection and testing and she still stands to make an impact in future research, as her remains will be utilized by scientists across the country for a variety of studies.

For example, the tissue from the shark’s brain was sent to Florida for mercury testing. While the results likely won’t reveal much about this specific shark, her tissue will go toward a larger study that will show whether the animal is at risk for mercury poisoning over its long lifespan.

Likewise, the shark’s DNA will be entered into a worldwide database that will seek to analyze the differences between the animal’s geographic populations between its distinct habitats in Pacific, Atlantic, African, Australian and other waters. The shark was also tested against a database of Atlantic white sharks observed by Massachusetts researchers, which showed no prior record of the shark.

The shark’s tissues and bones were cataloged for future studies and the university has received inquiries from researchers in Texas, Rhode Island, Florida, Massachusetts and other East Coast shark researchers.

Lankford said even the shark’s skin can reveal new clues as to its nature.

A UNCW student is researching the unique patterns of the shark’s scales with a powerful electron scanning microscope. The study will look at whether the scales change over different parts of the shark’s body.

“Shark scales are actually engineering the environment,” Lankford said. “They’re converting water flow into a linear pattern that reduces drag.”

And while the shark offered Lankford a unique opportunity to study the species, he still lamented that the animal died.

“It is really a magnificent creature. When you think about white sharks and what they do, it’s quite amazing,” Lankford said. “It’s sad to lose a member of the Atlantic population.”

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