ST. PETERSBURG, Fla., Jan. 1 (UPI) -- Marine biologists monitoring a sperm whale stranded at the mouth of Florida's Tampa Bay say euthanizing it is the most humane option.

The 25- to 30-foot whale has been floating around the Pinellas coastline since at least Sunday, when a commercial fisherman spotted it, the St. Petersburg (Fla.) Times reported Tuesday.

The whale being in water less than 9 feet deep is often considered a sign of distress, biologists said. The group monitoring the whale decided Monday to euthanize the mammal after its breathing became labored.

Mote Marine Laboratory spokeswoman Nadine Slimak said it would be more humane to euthanize the animal than to let it die on its own. The whale beached itself Sunday but made it back to water Monday. Biologists then tried to move it to deeper water but it wouldn't swim away, the newspaper reported.

The whale wasn't exhibiting any visible signs of trauma, such as bleeding, officials said.

"It's just floating there," Slimak said. "It's not doing any of its normal actions."