They're Back! Shark Migration Season Begins in S.E. Florida
They’re back! In the largest migration in U.S. coastal waters, blacktip sharks are headed south in the thousands for their annual migration off Florida’s southeast coast. For eight consecutive years, Stephen Kajiura, Ph.D., an internationally renowned shark researcher at Florida Atlantic University, has been observing and tracking these “snowbirds of the sea,” using a boat, a plane, acoustic monitoring devices, and now drones, to report their whereabouts in real-time. In prior years, the researchers have reported as many as 15,000 sharks on any given day. Odds are that anyone in the water will be within a 60-foot radius of one of these sharks.
Monitoring the migration patterns of blacktip sharks is not just about public safety — it’s also about ocean health. They sweep through the waters and “spring clean” as they weed out weak and sick fish species helping to preserve coral reefs and sea grasses. They come down south during the coldest months of the year and head north when it starts to warm up. Water temperatures determine where these blacktip sharks wind up. They leave the north when water temperatures drop below 71 degrees Fahrenheit and start heading south. They swim as far south as southern Broward County or northern Dade County and as far north as North Carolina.
“Last year, we saw a dramatic decline in the number of blacktip sharks that migrated south. In fact, it was so low that we estimated the population to be about one-third of what we have seen in previous years,” said Kajiura, a professor in the Department of Biological Sciences and director of the Elasmobranch Research Laboratory in FAU’s Charles E. Schmidt College of Science. “We want to make sure that these snowbirds come back to South Florida, because if they don’t, it will have a huge ecological impact in this region.”
Since water temperatures affect the migration of these sharks, studying the correlation of water temperatures and their migration patterns provides Kajiura with a powerful predictive tool. He uses small transmitting devices and web-accessible monitoring devices to receive the data in real-time via email notifications. Kajiura also uses a fixed-wing aircraft with a camera to capture photos and video of the sharks as he flies about 500 feet above the water going about 90 mph. South Florida’s crystal clear nearshore waters makes it easy to distinguish the sharks. He and his team can cover and record a field of view that’s approximately 650 feet wide and less than 15 feet deep. They capture these images and take them back to the lab to manually count the sharks on a computer screen.
“My research assistant has personally counted more than 100,000 sharks on the computer screen, which actually look like little black dots,” said Kajiura.
Kajiura has added drones to his arsenal of ocean-observing tools to provide additional data and different visual perspectives of these sharks to enhance his team’s ability to keep an eye on the oceans and census populations, and monitor animal responses to climate change.