Climate change is creating a battle of survival of the fittest. And it appears bull sharks are winning.
Research published this week in Scientific Reports documents a new bull shark nursery in Pamlico Sound, just off the shores of North Carolina. It’s basically 500 miles north of the previous northernmost nursery off Florida’s east coast, representing a big leap for one of the most badass sharks in the sea. The findings are also among the first to show marine predators expanding their range in response to environmental shifts.
The Pamlico Sound sits between the Outer Banks and North Carolina’s coast. The Pamlico River flows into it, create a mix of fresh and salty water in some parts, while its expanse contains seagrass, shoals, and other features that make it an ideal habitat for a number of sharks.
The new findings come out of a bigger effort over the past decade to see what sharks are using Pamlico Sound, and to map habitat suitability. But in the process of analyzing the data, Charles Bangley, the lead author of the study and a postdoc at Smithsonian Environmental Research Center, told Earther that a weird trend emerged.
Juvenile bull sharks were rarely caught or spotted in surveys prior to 2011. But in 2012, they started showing up regularly, and their numbers have grown since then. The fact that young sharks—either babies or juveniles—were showing up was a strong hint that something had changed.
“Adult Bull Sharks are highly mobile and range pretty widely but this species tends to be a bit pickier than other sharks with where they’ll give birth,” Bangley said in an email. “Pamlico Sound has the shallow depths, brackish areas, and limited access to the ocean that many already-known Bull Shark nurseries in Florida and the Gulf of Mexico have, so likely the only missing piece was warm enough temperatures during the pupping season in early summer.”
Waters in the sound have warmed the most in May and September, and that seems to be what’s driven the uptick in the number of bull sharks. Other research going back to 1965 backs up the fact that young bull sharks have been extremely uncommon in Pamlico Sound, historically.
From an ecological standpoint, the study is important because it tracks how climate change is messing with one of the most dangerous predators in the sea. Bull sharks eat everything, including other sharks.
“This gives them a potentially significant ecological role as predators of other predators, which could make them a key part of predator-prey interactions with effects that trickle all the way down to things like seagrass growth and nursery habitat for small fishes,” Bangley said.
Right now, it’s unclear what exactly the new bull shark nursery in Pamlico Sound will mean for species that traditionally call it home. In a blog post on Southern Fried Science, Bangley said he already has “plans to look at their diet” as well as how the sharks are interacting with other species as their numbers grow.
There’s unlikely to be a Jaws moment, though, in terms of the young sharks going after humans. Bangley stressed that though they’re “one of the more potentially dangerous shark species to humans,” the areas they’ve found sharks in the sound are far from where people tend to recreate.