Earth's Journal

Biosphere Journal Entry

Dolphins Stranded in Florida (March 8, 2005)


Photo of rough-toothed dolphins courtesy NOAA.

Over 100 rough-toothed dolphins became stranded in the Florida Keys this week. Most were adult females and young dolphins. At least twenty of the dolphins died.

The stranded dolphins were found on sand bars about a quarter of a mile from Marathon on Key Vaca. At low tide, the water was only about six inches deep.

Biologists with the National Marine Fisheries Service couldn't say for sure why the dolphins stranded. But wildlife experts were investigating if submarine sonar tests were to blame. A Navy sub was testing high-energy sonar about 45 miles from Marathon the day before the dolphins stranded. The loud sonar bursts can be heard for several miles in the water.

In the past, some beachings have been linked to underwater sonar tests that may damage marine mammals' ears or confuse them. Or, the blasts might frighten them and cause them to surface too quickly. The sudden change in pressure can form nitrogen bubbles in body tissue, a condition divers call the "bends."

There are other possibilities, including infection from red tide. Florida's had a big problem with red tide this year, especially along its southwestern coast. Scientists already know these toxic algae blooms are harmful to manatees and other animals. They're investigating other possible sources of infection from bacteria or viruses as well.

Some whale or dolphin beachings occur when the leader of a pod gets sick or disoriented. Other pod members may follow their leader to the shore. This is especially true with sociable species like the rough-toothed dolphin.

Another possibility is infection with parasites that affect the mammals' ability to navigate. Or, the whales or dolphins may be tracking prey that moves too close to shore.