The latest find is surprising because shark skeletons are made of cartilage—a rubbery tissue that doesn't preserve as well as bone.
The president retweeted the post just before midday amid a series of other retweets praising conservative radio personality Mark Levin's argument with Fox News host Ed Henry.
This isn't the first shark attack to occur in the waters of northeast Florida and southeast Georgia in recent months.
Photographer Joe Malt of Orleans, Massachusetts captured a surfer's close encounter with a shark on Nauset Beach this morning.
Blue sharks are considered "near threatened" globally, though there is no limit on catching them in the United Kingdom.
"I hope you enjoy your moment of glory," wrote one commenter, "and I hope for your sake karma doesn't come bite you hard the next time your out fishing for sharks."
"We simply believe that human life must be prioritised over the lives of sharks," head of the state government of Queensland, Australia, said.
At least three people were bitten in just a two-day period, including a surfer who landed on a shark.
"I was freaking out. I was like, 'He has no idea there's a shark right next to them," said photographer Matt Larmand.
"Obviously it was the most intense moment of my life," fishing guide Rob Gorta said.
The seal attack on Saturday marked the fourth time a shark has been spotted at Nauset Beach, leading to the closure.
About a half-a-dozen sharks were captured enjoying a feeding frenzy in North Carolina waters.
New Smyrna Beach on the state's central east coast is considered to be the shark attack capital of the world, according to the International Shark Attack File.
Blacktip sharks can grow up to eight feet long and nearly 300 pounds in weight.
Researchers say they were stunned by the close encounter.
The bluntnose sixgill is one of the largest sharks in the world and it has not changed much in around 180 million years.
"In the history of fisheries science, only two pocket sharks have ever been captured or reported," Henry Bart, director of the Tulane Biodiversity Research Institute, said in a statement.
The oldest embryo kills and consumes its siblings, causing it to grow exponentially bigger and stronger.
Jeff Weakley was bitten by an unidentified shark while surfing in the waters off Flagler Beach in 1994.
"Selfiecides" account for more than five times the number of fatalities, and the numbers are only rising.
Shark attacks 19-year-old surfer off the coast of North Carolina as he swam in the water with his brothers.
One-hundred percent of the profits go to saving the sharks.
The men were fired from their jobs over the violent incident.
A marine biologist says the footage of the sharks hunting is the best his team has ever captured.