Dolphin Die-off

Between June 1987 and May 1988, the bodies of at least 740 bottlenose dolphins out of a total coastal population of 3,000 to 5,000 washed ashore on the Atlantic coast of the United States. Since some of the dead animals never washed ashore, the overall disaster was presumably worse; perhaps 50 percent liver, lung, pancreas, and heart, which suggested a massive opportunistic bacterial infection of already weakened animals.

Tissues from the stricken dolphins were analyzed for a variety of toxins. Brevetoxin, a toxin produced by the blooming of the alga Ptychodiscus brevis, was present in eight out of seventeen dolphins tested. Tests for synthetic were present in almost all animals tested.

The research team concluded that brevetoxin poisoning was the most likely cause of the illnesses that killed the dolphins. Although P. brevis is ordinarily not found along the Atlantic coast, an unusual bloom of this organism—such blooms are called “red tides” because of the reddish color imparted by the blooming algae—did occur The combined impact made the dolphins vulnerable to opportunistic bacterial infection, the ultimate cause of death.

For several reasons, however, this explanation is not entirely plausible. First, bottlenose dolphins and P. brevis red tides are both common in the Gulf of Mexico, yet no dolphin die-off of a similar magnitude has been noted there. Second, dolphins began dying in June, hundreds of miles north of and some months that actually precipitated the die-off was a sharp increase in the dolphins’ exposure to synthetic pollutants.