Endangered sawfish die-off in Florida Keys baffles scientists
SUGARLOAF KEY, FLA. >> Fishing guides in the Florida Keys began reporting unusual sightings to Ross Boucek in the fall. Small bait fish, especially at night, would start spinning in tight circles in the water, seemingly in distress.
As the months went by, more reports trickled in to Boucek, a biologist with the Bonefish & Tarpon Trust, a nonprofit conservation group. Bigger fish — jacks, snook — were swimming in spirals or upside down in the shallow waters of the Atlantic Ocean and Gulf of Mexico. So were stingrays and the occasional shark.
Boucek called scientists at state agencies and universities. They held meetings, took samples of the water and fish and tried to figure out the cause
In January, the ailment began afflicting smalltooth sawfish, a type of large, prehistoric-looking ray named for the look of its snout-like rostrum lined with sharp teeth. The sawfish, which are endangered and reliably found only in southernmost Florida, started dying.
The search for answers became urgent, Boucek said, “the second an endangered species started dying off at unprecedented rates.”
He now spends much of his time collecting samples
and recording data from sensors that he deploys along the sea bottom, looking for changes or patterns that might help solve the mystery.
At least 38 sawfish have died this year, according to the Florida Fish and Wildlife Commission, which is investigating the deaths. Perhaps only hundreds of breeding sawfish females remain in the wild, said R. Dean Grubbs, a fish ecologist at Florida State University. The fish can grow as long as 18 feet, according to the commission. A research team led by state scientists has raced to conduct experiments, tag sawfish and sample their blood. Florida lawmakers designated $2 million in emergency funds to help carry out the work.
But scientists have not yet figured out what is going on. They have ruled out a few potential causes, including red tide, the toxic
algal bloom that has led to past massive fish kills.
Some wonder if the summer's record-breaking sea temperatures, which bleached coral throughout the Keys, may have altered the ecosystem and triggered unusual microalgal growth.
In their best lead to date, they have learned that microalgae naturally present near the sea bottom have produced an elevated level of toxins that acutely affect the neurological systems of fish when they swim into those areas.
That might explain why spinning fish seem to recover when pulled up from the sea bottom (where toxin concentrations are higher) toward the water surface (where concentrations are lower), said Michael Parsons, a marine science professor at Florida Gulf Coast University. Sawfish are sea-bottom dwellers.