Humans needn't worry, a researcher says. The sharks are far from beachgoers. Besides, baby bull sharks don't bite.
There's a baby boom in the warming waters of North Carolina's Outer Banks, in the rivers and bays that branch out from the Pamlico Sound. They are tiny. They are cute. They are bull sharks.
Drawn by a temperature rise in coastal waters, a result of climate change, bull sharks that prefer warmth and water with lower salinity levels have taken to mating in the sound near Carolina's popular beach haven, and juvenile sharks are showing up where they have rarely been seen before, a new study says.
Humans shouldn't be alarmed, a researcher said. The nurseries are established in remote areas such as Long Shoal River and Rose Bay, far from the beach action in Kitty Hawk and Cape Hatteras. Besides, the babies don't bite.
Researcher Charles Bangley said adult bull sharks, so named because of their stocky, barrel-chested build, swim along the Atlantic coast and have been spotted in the sound by fishermen for decades. But juveniles were uncommon, even in gill net surveys undertaken by scientists between 2001 and 2011.
But in 2011, there was "a slightly higher number of bull sharks . . . and a spike the year after," said Bangley, a marine scientist at the Smithsonian Environmental Research Center in Maryland who was the study's lead author. The number kept rising up to 2016, establishing a pattern. "We kind of have a before and after in our data set." The study was published Monday in the journal Scientific Reports.
The study was an offshoot of a larger survey of 12 shark species, including the four-foot smooth dogfish, the spiny dogfish and Atlantic sharpnose shark - all relatively small. The sandbar shark is the largest of that study, published last week in the journal PLOS One.
A bull shark nursery in the Outer Banks raises eyebrows because Florida is the Atlantic's haven for bull shark nurseries. The barrier islands near Cape Canaveral are where most are born. There are also several nurseries between the Florida Keys and the Everglades and Tampa Bay. South Carolina has a massive shark nursery, but it does not have bull sharks.
Bull sharks like water temperatures at 68 degrees or a little warmer. Juvenile bull sharks hang around the area where they're born for about four years. It's safer there in the tepid, less salty water that isn't tolerated by other shark species that might eat them. Then they swim off to join adults that glide up and down the Atlantic and Gulf coasts.
Those early days in the near-freshwater nursery is why adult bull sharks maintain an affinity for bays and rivers. They have been spotted as far north as Long Island and deep into the rivers of the Chesapeake Bay. "Bull shark migration patterns are poorly understood," Bangley said, noting it was a subject for a future study.
"Juvenile bull shark presence in the sound was strongly related to early summer temperatures and late summer salinities, which have increased in the estuary over the 13 survey years," the study said. "Further evidence for increasing water temperatures in Pamlico Sound was found in a 45-year data set for the North Carolina Division of Marine Fisheries estuarine trawl survey."
The results suggest higher water temperature "allowed bull sharks to expand their nursery habitat. This shift will have unknown, but potentially strong, impacts on both the local ecosystem and interactions with humans," the study said.
Human and shark encounters overwhelmingly result more often in the death of the shark. Shark attacks of all kinds in North Carolina have been exceedingly rare. In 2015, Bangley said, there were eight bites in summer, none of them fatal, mostly in the sound, not in the Atlantic, where beachgoers frolic.
"As as far as I know, no bites on a swimmer inside the sound," Bangley said.