What may have caused a mighty great white shark, one of the ocean’s greatest predators, to end up on our shores? That’s what marine biologists at UNC-Wilmington are still trying to figure out after a necropsy performed on the animal Tuesday showed no obvious signs of life-threatening trauma.
According to Dr. Thomas Lankford, an ichthyologist and associate professor in the university’s marine biology program, a cause of death could not be determined based on an initial examination of the shark.
“Our first concern was whether this animal had contact with humans or fishing equipment,” Lankford said. “We found no evidence of entanglement in fishing nets or of any hooking injuries.”
Lankford said that injuries to the great white’s exterior, which included bite marks, lacerations and a missing fin, were not implicated in the cause of death.
“It appears damage to the left pectoral fin was a result of post-mortem scavenging by other sharks,” said Lankford, who estimates that the shark had been dead for three or four days before it washed up Monday on the south end of Wrightsville Beach.
An internal probe, which included the removal of the great white’s liver, heart and intestines, also showed no obvious cause of death.
“There was no evidence of disease,” Lankford said, noting that this specimen’s large liver was a sign of good nutritional condition. “All the animal’s internal organs appeared healthy.”
While further testing of the samples taken from the shark are needed to determine a cause of death, Lankford said other conclusions were made. The digested remains of a large black drum fish, which Lankford said can be found in local waters, were found in the animal’s stomach and indicated that it had been a week since its last meal. The female was also determined to be a juvenile based on its reproductive organs.
“Its ovaries were consistent with immature status,” said Lankford, who said that great white sharks can take 25 to 30 years to fully mature. “Based on its size, we approximate that the shark was around 20 years old.”
Samples of the shark’s vertebrae will be tested to confirm the animal’s age, according to Lankford. Tissue samples were also collected for genetic testing, which help scientists and researchers analyze the populations both along the Atlantic Coast and worldwide. Lankford said that he’s already received requests to study the shark’s brain for mercury levels due to the species’ preferred diet of fish.
“It’s not clear what effect mercury has on white sharks,” Lankford said when asked if mercury is as poisonous to them as it is to humans. “That’s one of the things this rare event provides us with the opportunity to research.”
Though there’s plenty of work ahead for Lankford, he has lots of help. Bill McLellan, who runs UNCW’s Marine Mammal Stranding Program, helped lead Tuesday’s necropsy at the Oriole Burevitch Lab on campus. Assisting was a group of 20 graduate and upper-level undergraduate students from UNCW, East Carolina University and UNC-Chapel Hill’s Institute of Marine Sciences in Morehead City as well as representatives from the North Carolina Aquarium at Fort Fisher and shark research and tracking group OCEARCH. About a hundred more observed the necropsy over the duration of the five-hour process.
“It was a terrific opportunity for our students. It was very meaningful for them,” Lankford said. “We do not see many strandings of great white sharks on our North Carolina coast, so this was special.”
Students were involved in taking samples, dissecting the animal and also in photographing the specimen. The photographs will be compared to a database of sharks put together by the Atlantic White Shark Conservancy in Massachusetts to see if this particular animal, which Lankford said was not tagged with a tracker based on their evaluation, had been documented before.
Lankford said the entire body of the shark was being used for research since there is so little information on the rarely seen species. Even the total number of great whites in the world is disputed by scientists, with some estimating that the global population could be as low as 3,500.
“It’s difficult to know exactly how many are present,” said Lankford. “That’s why this experience is so valuable. It was a privilege to have this opportunity to collect information, and we’re looking forward to sharing it with others.”