‘The new normal?' What the die-off mystery in the Keys means for endangered sawfish

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3 days ago

Nearly two years after one of the planet's rarest fish began washing up dead in the Lower Keys, scientists investigating the deaths say one thing seems certain: whatever caused it will likely be around for years to come.
'We're gonna probably have this tax on the sawfish population indefinitely. We're now introducing a new component of natural mortality that's going to kill somewhere between X and Y number of sawfish,' said Ross Boucek, a marine biologist with the Bonefish and Tarpon Trust. 'The question is how do we recoup that tax?'
To do that, they'll need to better understand conditions caused by an ocean heat wave that slammed Florida before the deaths, and to try to find ways to prevent them.
READ MORE: As sawfish deaths mounted, wildlife officers and researchers scrambled to respond, records show
Months after the record-breaking summer heatwave, which killed coral, seagrass and other marine life, endangered smalltooth sawfish began dying in the winter of early 2024, mostly in the Lower Keys.
Boucek, who earned his doctorate looking at impacts from extreme climate events like hurricanes, temperature changes and drought, said scientists feared the prolonged high temperatures would ignite such cascading events.
'With extreme events, there's always going to be some unpredictability to what the ecological response is, which makes them very challenging because you've never seen them before,' he said. 'When you have them, you expect this weirdness to follow.'
Florida sawfish once roamed waters from the Indian River Lagoon north to the Carolinas. But loss of habitat from developing coasts and getting caught in commercial fishing nets and longlines nearly wiped them out. Today, they can mostly be found only in South Florida.
Eventually, at least 64 sawfish were confirmed dead amid hundreds of reported sightings of sick sawfish.
Signs of looming trouble appeared in the Lower Keys months before the sawfish started dying when fishing guides started seeing dozens of other species spinning and showing signs of distress. Few died, so the mysterious ailment was concerning but not alarming. Then sawfish began washing up dead in the same shallow waters, launching an unusual rescue effort. Scientists suspected a bottom-dwelling algae early on after they detected higher than normal levels as part of an ongoing monitoring effort to look for ciguatera. Sawfish belong to the ray family and feed on the sea floor, so it made sense.
'T his heat wave changed something for this algae,' Boucek said, which can bloom and become toxic with an increase in nutrients from either leaky septics and storm run-off, a fish kill or seagrass die-offs. Or, he said, 'something happened to its predators.'
That became the prevailing theory — that whatever kept the algae in check was harmed by the extreme heat.
'If there's no cops to keep the bad guys in line, things can proliferate,' he said. 'So the question is, was it nutrients that caused this or was it something that happened to its controlling agents.'
Various species of fish later tested found levels of the toxin, along with others that may have interacted to sicken fish.
Florida lawmakers provided $2 million to launch an investigation as the deaths mounted. BTT received $1.75 million that it used to set up surveillance measures, tag and track sawfish and begin testing waters. In the fall of 2024, as waters cooled, Boucek said scientists and guides braced for another round of deaths, although some debated whether it would strike again without such a severe heat wave.
'It could be it was this temporary ecological response that we saw, where we have this reverberation of the system,' he said. 'It happens once and then we don't ever see it again at the same intensity.'
Then in November, Boucek spotted the first spinning fish. Other sightings followed. In late December, a dead sawfish was found. But by January, things quieted down, with far fewer dead sawfish. By March, the month sightings peaked the year before, there were only about half the number of reports for spinning fish and less than a dozen dead sawfish.
Scientists monitoring water also didn't see spikes in levels of the toxic algae that they saw the year before.
Boucek said that suggests a number of things: a different toxic algae could be involved. Or it could be that the dead sawfish had been infected during the previous event and were just now dying. It could also mean that there just weren't very many of the endangered fish left for the algae to kill.
While scientists continue to look at the source of the toxin and what triggers it, Boucek said a closer look is needed to understand the current sawfish population so it can be better protected.
Charlotte Harbor was once considered the main area where sawfish gave birth, and the focus of much of the state's research. But it's possible sawfish critical habitat extends much further, south to Naples, throughout the Ten Thousands Islands and in the shallow bays, creeks and flats in the Everglades and Florida Bay.
'The question really is was that entire southwest coast a nursery habitat or a juvenile habitat for them at one point in time, but now the only places that are available are the ones that are protected and not developed,' he said.
Restoring and protecting those areas could help stabilize the population and also benefit tarpon, snook and other fish that share the same waters, he said.
That would help prepare for the next time.
'Is this going to be the new normal?' he said. 'If it comes back at the same intensity that it did in the past, I mean we can't lose 54 sawfish every year.'
This story was originally published by WLRN and shared in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the Sun-Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times
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