Biscayne Bay, shallows waters off the southern Everglades and tiny Tavernier Key have been added to a landmark global map that for the first time identifies areas critical to the survival of disappearing sharks and rays.
In the works for the last four years by the International Union for Conservation of Nature (IUCN), the project relied on standardized criteria that could apply planet-wide.
Altogether, more than 1,000 locations were mapped, with a goal of improving management. None of the designations add restrictions, like marine preserves or fishing regulations, but highlight why certain areas help imperiled species persist.
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Armed with decades of research, scientists in South Florida determined that Biscayne Bay’s shallow waters, dotted with seagrass meadows and remnants of old reef, provide an important nursery for 13 shark and ray species, including eight on the IUCN’s red list for threatened species.
Among those documented: pregnant or baby bull, tiger, black tip and sandbar sharks. Great hammerhead sharks, which the IUCN considers critically endangered, also use the bay in the only formally documented nursery for the species on the U.S. east coast.
Whitewater Bay and waters from Ponce Inlet to west of Flamingo likewise provide critical pupping grounds for endangered sawfish, which suffered an unprecedented die-off in 2024 after a mysterious disease left dozens dead. The mapping also identified a corridor extending to deeper waters from Tampa Bay to Cape Canaveral as important to sawfish.
"Biscayne Bay is Miami's backyard. But it's still critically important to a lot of different species of shark and ray.”Catherine Macdonald.
Tavernier Key, east of Plantation Key, acts as a rare refuge for white-spotted eagle rays, the study found.
”Here in Miami, one thing that I hope this designation will mean is that people will recognize the ecological importance of [Biscayne] Bay,” said Catherine Macdonald, director of the Shark Research and Conservation Program at the University of Miami.
”People don't think that things live here, right? That the bay is sort of a swimming pool that's been denuded of life. In fact, it's an incredibly ecologically diverse, complex, and important place.”
To document the sites, scientists deployed a range of tools, from taking blood samples to attaching acoustic trackers.
Macdonald spent nearly 10 years compiling data that showed pregnant sharks often seek shelter in the bay to have their pups. That included conducting ultrasounds on female sharks, examining their bodies for bites left during mating and launching drones to better tracks sharks across the 270 square-mile bay. Her team also took blood samples and checked DNA.
To qualify for the map, Macdonald needed to show species either used the bay for reproducing, for feeding or gather in large numbers, even if why was unclear.
”Biscayne Bay meets all three of those criteria for at least one species, but meets at least one of those criteria for 13 species of shark and ray,” Macdonald said.
'Pretty uncommon'
What makes Biscayne Bay such a hot spot is a combination of lots of food and warm waters good for gestating pups. The risk of being eaten by another, larger fish is also low, she said.
“They don't love spending their time in very shallow water for the most part and that creates some habitat separation that gives juveniles refuge from potential predation by larger sharks,” Macdonald said. The average depth of the bay is just six feet.
Having the designation made now matters as development pressure increases around bay waters. That includes at least three large marinas, with plans at the shuttered Seaquarium calling for slips to accommodate yachts up to 200 feet long that could damage the shallow bottom.
”In general, Biscayne Bay regulations are broadly harmonized with state regulations and in cases where the state has done a really good job thinking proactively about protecting sharKs – which I think there are many examples of – we already benefit from those choices,” Macdonald said. “I'm hoping that this will help motivate investments in habitat protection.”
That's not always been the case over the years. In 2015, Biscayne National Park included preserves in a new management plan to better protect sensitive areas for fish. But that plan was derailed by political blowback when state officials opposed it. Two years ago, a federal judge ordered the park service to move forward.
While individual species are protected by various regulations, which also limit some development to protect habitat for manatees or seagrass, broader recognition as a critical area specifically for sharks and rays has remained elusive.
”We think about important habitats as being remote and protected from human influence. You know, pristine,” Macdonald said. “Biscayne Bay is Miami's backyard. But it's still critically important to a lot of different species of shark and ray.”
Other areas provide mating or nursing grounds, she added, “but to have so many juveniles in this urban environment of a diverse group of species is pretty uncommon.”
Even without restrictions, she said some easy household fixes could help baby sharks and rays: limit fertilizer and pesticide use during the rainy season and keep garbage out of waterways.
Also, boating safety that avoids tearing up seagrass beds and bay bottom “can all help make Biscayne a better place to live for people and for sharks.”
