Scientists have reported a change in the migratory patterns of blacktip sharks – and climate change is the most likely reason.
Blacktip sharks (Carcharhinus limbatus) spend most of their time in Florida. In summer, the sharks head north to cooler waters. In previous years, they would head to the Carolinas. A few years ago, however, the sharks started swimming further north to Long Island in New York.
Stephen Kajiura, a shark expert with Florida Atlantic University, has been following the sharks’ migrations since 2011. He has used a plane to survey the Florida coast as the sharks travel north. It’s not just a few sharks, either. Thousands of sharks that make up about 25 to 30 percent of their total population make the annual trek north.
Researchers had also tagged some of the sharks so they could follow their movements. In 2016, the sharks made their first trip to Long Island. Scientists initially dismissed the change as a fluke, but the sharks have been going to Long Island every year since then.
Kajiura hypothesizes that there are two possible reasons for the sharks’ new preference for Long Island – and both involve climate change. Temperatures along the Atlantic Seaboard between the Gulf of Maine and Cape Hatteras, North Carolina, have increased by 3.6 degrees Fahrenheit (2 degrees Celsius) since the 1960s.
Blacktip sharks are ectotherms, which means they can’t regulate their body temperatures the way mammals can. If they get overheated, they need to seek cooler waters. Blacktip sharks feed on fish, and fish are also ectotherms. Thus, the sharks may simply be following their prey as they head north to cooler waters.
The sharks’ move could pose problems for human vacationers. A full-grown blacktip can be anywhere from four to eight feet (1.2 to 2.4 meters) long. They also like shallow water – which increases the chances of swimmers getting bitten. People who are bitten by blacktips generally don’t die or lose limbs, but they often end up with a mangled foot or hand.
