Tampa Bay sees first sawfish death amid mysterious South Florida die-off

A mysterious die-off of sawfish in the Florida Keys hit home this week, according to the Tampa Bay Times .

Why it matters: Smalltooth sawfish, known for their long snouts lined with teeth, have been endangered since 2003. They were the first marine fish to receive federal protection, per NOAA .

• At least 53 sawfish have died so far this year, the Times reported. More are believed to be sick, and other species including stingrays, sharks and groupers have also been affected.

Catch up quick: Observers in November began reporting abnormal fish behavior. Smaller species like pinfish, a popular bait fish, were spinning and swirling erratically.

• Scientists confirmed the first sawfish death in January, per the Times.
• Videos showed the animals displaying the same odd spinning behavior, and a hotline in the Keys to report sightings has been ringing daily.
• Federal scientists in April began an emergency mission to rescue the sick sawfish.

The latest: Scientists are currently eyeing algal blooms as a potential cause of the die-off, according to the Times. They've already ruled out red tide, water temperature and salinity.

Zoom in: Recently, a team of shark researchers — for the first time ever — caught and tagged a healthy adult sawfish offshore in the Tampa Bay area, the Times reported.

• They hoped comparing the animal's healthy blood to the blood of sick sawfish found in the Keys could provide some clues as to what's causing the die-off.

Yes, but: As they set off on another expedition last week, a report came in of another adult sawfish sighting off the beach at Bay Pines.

• This one appeared distressed, showing the same spinning behavior as the other sick fish. The crew tried unsuccessfully to rescue it.

By Monday, the fish had washed up dead along the shoreline. It marked the northernmost report of a sawfish death, per the Times.

Between the lines: Scientists don't believe the disease is spreading north.

• The latest thinking is that the fish are getting sick in the Florida Keys and swimming north for the summer.