Biscayne Bay has been identified as a crucial habitat for critically endangered great hammerhead sharks (Sphyrna mokarran), supporting them from birth through adulthood, according to a new study.
The eight-year study shows that juvenile great hammerhead sharks depend on the shallow waters of bay – sheltered in the heart of the Miami metropolitan area – during their earliest and most vulnerable years.
The findings, published in the journal Ecology and Evolution, also reveal that older sharks return to the Florida bay seasonally, making it a key site through their entire life cycle.
Hammerheads in Biscayne Bay
Biscayne Bay is a subtropical estuary rich in marine life. However, it faces growing threats from urban development, pollution and declining water quality. These pressures could have serious consequences for the species that depend on it, not least great hammerhead sharks, say researchers from the University of Miami.
In a bid to learn more about how the great hammerheads are affected, the team analysed the feeding and habitat use patterns of 62 individuals between 2018 and 2025.
“Our team employed a research technique called multi-tissue stable isotope analysis to track both short and long-term resource use, allowing us to gain new insights into the species' dietary habits across different life stages," says John Hlavin, lead author and doctoral student at the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science.
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The study found that juvenile sharks feed mainly on small inshore stingrays in the bay for up to two years.
After that, subadult sharks move out to forage on coastal reefs but still return to the bay in late spring and early summer. Some adults continue to feed on bay species, showing its long-term importance.
The study raises concerns about fishing activity in the area. Great hammerheads are highly sensitive to capture stress, and the bay is a popular recreational fishing spot, says Hlavin.
“Reducing interactions with these sharks – particularly avoiding catch-and-release fishing in key nursery areas – can dramatically improve survival for this endangered species,” he concludes.
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