Smalltooth sawfish in Florida are spinning and beaching themselves in strange, mystery die-off

Endangered smalltooth sawfish in Florida are erratically "spinning and whirling" in shallow waters, causing them to strand themselves and die. The "abnormal fish behavior event" currently defies explanation, scientists say.

"There have been over a hundred unique reports of affected sawfish and now over 30 confirmed mortalities," Adam Brame, the sawfish recovery coordinator at the National Oceanic and Atmospheric Administration (NOAA) Fisheries, told Live Science in an email.

The ongoing mortality event began in October 2023 along the coast of the Florida Keys, and so far 32 smalltooth sawfish (Pristis pectinata) have died, although NOAA officials believe that this is an undercount, according to a statement. Deaths have resulted from sawfish "essentially stranding themselves" on beaches, Brame said.

Footage posted to Facebook on April 1 shows a smalltooth sawfish spinning near the shore.

Water samples didn't reveal any irregularities in water quality or levels of inorganic or organic chemicals. However, tests identified elevated concentrations of dinoflagellates from the genus Gambierdiscus, according to Bonefish & Tarpon Trust.

Related: Largest recorded smalltooth sawfish washes up dead in Florida

Dinoflagellates are microscopic, single-celled algae that can sometimes appear in large concentrations in the water — known as algal blooms. Some algal blooms are harmless, but some algae, including Gambierdiscus species, produce neurotoxins that can be harmful to people and Animals in the area.