LITTLE ROCK — Was it the oil? That’s the question as the number of stillborn or dead young dolphin calves washing up on Gulf of Mexico shores continues to rise.
The research team called in to investigate says we might never know.
On Friday, five more dead baby bottlenose dolphins were found in Mississippi and Alabama, pushing to 67 the number of dolphin carcasses tallied since Jan. 1 on beaches from Louisiana to the Florida panhandle. Of those, 35 are so young that they might be spontaneously aborted fetuses, making this “unusual mortality event” even more unusual, though not unprecedented.
But determining the cause of this, or any other, wave of dolphin deaths is a huge challenge.
There are no witnesses to interview. The whereabouts of the dolphins before they died is unknown. Any unusual behavior preceding death went unobserved.
And, worst of all for the federally coordinated team investigating the dolphin deaths, all the carcasses are badly decomposed.
“A lot of the organs are mush, basically,” said Blair Muse, who collects reports of beached dolphins in the southeastern United States for the National Marine Fisheries Service. “They are coming ashore decomposed. It may prohibit us from determining the cause unless we get some fresh bodies.”
That’s bad news for the teams scouring beaches to collect whatever blood and tissue samples they can, the laboratories rushing to analyze those samples and the scientists who will eventually try to piece together the spotty evidence.
Those limitations also explain why the record of determining the cause of mass marine mammal deaths has not been good.
Since 1991, when the National Oceanic and Atmospheric Administration formed a marine mammal quick-response team, there have been 50 large-scale death events with seals, whales, manatees and dolphins in U.S. waters. Most of them involved a few dozen recovered animals - and most likely, many more that were never found.
National Oceanic and Atmospheric Administration-directed teams could determine the cause of death in just half those cases.
Of the 50 previous events, 14 involved bottlenose dolphins in the northern Gulf of Mexico and Florida, agency records show. Investigators could pinpoint the trigger in only five of those events.
Four of those mass die offs occurred in Florida after blooms of toxic microbes called red tides. Examination of the dead dolphins’ stomachs revealed high concentrations of a toxin produced by the red tide.
But such obvious evidence rarely surfaces.
In this case, as others, viruses are a prime suspect. In 1987 and 1988, some 700 bottlenose dolphins washed ashore from New Jersey to Florida, a wave of death ultimately pinned on the morbillivirus. The same virus decimated dolphins in the Mediterranean Sea from 1990 to 1992.
Muse said the NOAA-directed investigative team will also search for signs of another virus, Brucella, which causes spontaneous abortions in livestock.
By a process of elimination, the scientists will, over the coming months, try to winnow the list of suspects.
One of the researchers leading the investigation holds out more hope than his colleagues that the cause of the die-off will ultimately be found. Moby Solangi, director of Institute for Marine Mammal Studies in Gulfport, Miss., said his colleagues have recovered tissue samples from six of the dead calves.
“It’s very plausible that we will come to some sort of conclusion,” he said. “It’s something happening in one age-class of animals. Whatever happened, it affected the reproductive system and pregnancy.”
Despite the public interest in the case, Muse said, the deaths are not unprecedented. In 2007, 68 dead dolphins washed ashore in Texas. Most were calves, including many very young ones. The investigation was inconclusive, although Muse said researchers suspected a virus.
In any case, Randall Wells, chairman of the National Oceanic and Atmospheric Administration-organized working group providing guidance to investigators, advised patience. He said the huge popularity of forensics-heavy crime shows on television has led the public to expect instant results, whereas investigations undertaken with limited information might require months.
“People are rushing to try to say it’s the oil,” Wells said. “While that might be the case, it’s really premature to say that right now.”
Front Section, Pages 4 on 02/27/2011