Excerpts from an article in the NY Times
Studies show that dispersants, which break down oil into tiny droplets and can also break down cell membranes, make oil more toxic for some animals, like baby birds. And the solvents they contain can break down red blood cells, causing hemorrhaging. At least one fresh dolphin carcass found in the Gulf was bleeding from the mouth and blowhole, according to Lori Deangelis, a dolphin tour operator in Perdido Bay.
Another dolphin, its ribs broken, was hit by a boat, a catastrophe that dolphins are normally nimble enough to avoid. The veterinarian, Dr. Connie Chevis, found a tarlike substance in the dolphin’s throat. The substance will be analyzed to see if it is oil, but one theory is that the animal could have been disoriented by oil exposure, which can have a narcotic effect, rendering it incapable of avoiding a boat strike. Ms. Deangelis said the dolphins on her recent tours have been “acting like they’ve had three martinis.”
Despite an obvious suspect, oil, the answer is far from clear. The vast majority of the dead animals that have been found — 1,866 birds, 463 turtles, 59 dolphins and one sperm whale — show no visible signs of oil contamination. Much of the evidence in the turtle cases points, in fact, to shrimping or other commercial fishing, but other suspects include oil fumes, oiled food, the dispersants used to break up the oil or even disease.