The cause of death has not yet been determined for baby dolphins that have washed up by the dozen on beaches in Alabama, Mississippi, and Louisiana during the past two months. But cold water shock, which may have caused a spate of stillbirths, is one new theory to place alongside suspicions that the die-off is related to last year's Gulf oil spill.
Researchers at the independent Dauphin Island Sea Lab, in Alabama, have noted two instances of dramatic drops in water temperature that correspond to unusual snow runoff into Mobile Bay in January and February, and they suggest the sudden change may have caused calving dolphin females to abort.
Water temperatures fell quickly from 60 degrees F. to 45 degrees as flood volumes of water surged into the Gulf, the researchers say. Already, the infant mortality rate for the area's 5,000 bottlenose dolphins is 10 times the yearly average. This is the female dolphins' calving season.
Stillborn baby dolphins have been found over a swath of beach 200 miles long. Researchers say their deaths seem to correspond to two separate pulses, or freshets, of cold water that surged into Mobile Bay, after record 2011 snowfall across northern and central Alabama melted and poured into the Mobile River watershed.
The first freshet, in mid-January, corresponds with the first findings of dead dolphins. A larger number of dolphins began washing ashore in mid-February, shortly after the second major runoff began. Large areas of the Deep South received record amounts of snowfall this year.
“For these animals, that second freshet was the sucker punch," Sea Lab biologist Monty Graham told the Mobile, Ala., Press-Register. "You can see from the temperature and salinity signature that it blasted through the bay from the top to the bottom with that cold water. The temps dropped so fast and the river water was moving so fast, these animals wouldn’t have had a chance to swim out of the way. They were swimming in really cold water within 24 hours. That’s just a real shock to the system.”
When news of the dolphin deaths first emerged, environmentalists speculated that last year's massive Gulf oil spill could be the culprit. The National Oceanic and Atmospheric Administration has declared the die-off an "unusual mortality event" and is also investigating the deaths. So far, no signs of oil contamination have been found on the animals.
Scientists and environmentalists continue to debate the oil spill's possible long-term effects on the Gulf's fragile ecosystem, and what it all means for the human denizens of the Gulf Coast. At a meeting this week of the federal Gulf Restoration Task Force in New Orleans, activists and residents raised anew concerns about ongoing health problems they blame on petrochemicals in the water and air.
Dauphin Sea Lab researchers haven't discounted the possibility that there may be other causes for the dolphin deaths, including the presence of oil in the food chain. Skeptics say the cold water theory is unlikely, because pregnant dolphins should have been able to swim away from the area and into warmer waters.
By the end of last year, about 7,000 dead marine animals had been collected from the oil spill area. That compares with some 250,000 dead animals recovered after the Exxon Valdez ran ashore in Alaska in 1989.