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Biscayne Bay Is Busy and Polluted. So Why Are There More Sawfish?

Sunrise showing a fish kill in Biscayne Bay
Courtesy of Kathryn Mikesell
A fish kill spread across northern Biscayne Bay near Morningside on Monday.

Biscayne Bay has had its share of woes in recent years: a fish kill this summer, acres of dead seagrass and persistent algae blooms fed by increasing pollution.

But sawfish, a prehistoric-looking ray with a snout shaped like a chainsaw, don’t seem to mind.

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A new study by the University of Miami and National Oceanic and Atmospheric Administration has found sightings of the disappearing fish increasing in Biscayne Bay. The study, published this month in the online journal Endangered Species Research, is the first to track sawfish in the busy bay, which had previously not been considered an important habitat.

“What's interesting about Biscayne Bay is we have this massive city along its shores, this urban gorilla in the room,” said lead author Laura McDonnell, a researcher at UM’s Abess Center for Ecosystem Science and Policy.

Yet, despite the busy boat traffic and increasing pollution, numbers documented by the team are up even in the bay’s most urban spots, including South Beach.

“We had them on Brickell. We had them near Mercy Hospital. So they're they're not really keeping a distance from us,” McDonnell said.

The question is why.

A new study for the first time tracking smalltooth sawfish in Biscayne Bay found sightings are increasing, suggesting the bay may provide an important migratory route or other critical habitat.
National Oceanic and Atmospheric Administration
A new study for the first time tracking smalltooth sawfish in Biscayne Bay found sightings are increasing, suggesting the bay may provide an important migratory route or other critical habitat.

Smalltooth sawfish once roamed from New York to Texas, growing up to 18 feet long. They were so plentiful in the Indian River Lagoon that a 1884 report documented 300 caught in a single fishing season. But their numbers began plummeting in the 1980s, according to a 2000 status review. Wildlife managers blamed commercial fishing — nets often snagged their toothy saws — along with trophy hunters and loss of habitat.

In 2003, they were added to the endangered species list. That listing included protected habitat on Florida’s Gulf Coast and in Florida Bay, along the state’s remote southern tip and Florida Keys. But not Biscayne Bay.

“This is really because tracking efforts have shown that they spend relatively little time here compared to those other areas,” McDonnell said. “Nobody's really looked at how much time they're spending in Biscayne Bay and what they might be doing while they're here.”

But more sightings in recent years piqued scientist’s interest. Pollution problems had also drawn attention and prompted NOAA to designate the bay an area for special focus and increasing research projects.

For the study, researchers looked at both recent reports and dug up historic accounts, including newspaper reports dating to the 1800s. They also used acoustic monitors to track the movements of sawfish tagged as part of a shark monitoring program.

Altogether, the team collected 90 reports. Of those, more than half occurred in the last decade. That increase is partly due to better monitoring efforts and a state campaign to report sightings, the study said. But an increase in just the last four years could suggest Biscayne Bay is drawing more sawfish, the study concluded.

McDonnell said Biscayne Bay’s south end shares many of the same features as Florida Bay, the Keys and the Gulf Coast that make it such a good nursery for young sawfish: lots of mangroves and freshwater flowing from onshore.

But they're also turning up in unexpected places.

“What's most interesting is that we're able to show that not only are sawfish here, but they're occupying these waters that are considerably more urbanized. Anyone who's been out on Biscayne Bay knows what the boat traffic looks like, what the pollution can look like and they coming back with regularity,” McDonnell said.

She said some disappear soon after they’re detected and some hang around.

“So it's possible that this is a migration corridor of some sort,” she said.

An increase in sightings coincided with the COVID-19 shutdown, which McDonnell said helped researchers pinpoint sawfish movements.

“Whether the sawfish were coming closer because there was less activity in the water, or if they were there anyway and we just happened to have more eyes on the water, it’s really great we have more people aware of these things and have cameras in their pockets at all times,” she said.

Sawfish sightings can be reported by calling 1-844-4SAWFISH or emailed to sawfish@myfwc.com

Figuring out how sawfish use the bay, McDonnell said, will be the next step to help improve conservation efforts.

“These waters are not pristine and there's lots of questions that can be asked here,” she said. “What role does this area serve and what are the effects of urbanization and coastal development on this super rare and endangered species? We want to know what are they doing here? Why are they coming here?”

Jenny Staletovich is WLRN's Environment Editor. She has been a journalist working in Florida for nearly 20 years. Contact Jenny at jstaletovich@wlrnnews.org
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