Scientists try to explain rash of baby dolphin deaths in Gulf

A rash of baby dolphin deaths in the Gulf of Mexico has worried federal marine scientists, who are trying to come up with theories to explain the mystery.

So far this year, 29 fetal-sized calves have been found dead on the beaches of the northern Gulf. A typical year sees only two such reports, usually in March, says National Oceanic and Atmospheric Administration official Teri Rowles. She adds that it's too early to tell whether the deaths are tied to last year's Gulf of Mexico oil spill.

Rowles calls the surge of deaths, most likely from stillbirths, "very concerning."

Over the last two decades, federal officials have tracked 51 incidents of "unusual mortality events" in dolphins and manatees, most often tied to "red tide" toxins from coastal algae blooms, which afflict the Gulf of Mexico every summer. But none in the past has been linked to surges in deaths of dolphin calves.

"We don't want to jump to conclusions on what is causing this," says conservation scientist Randall Wells of the Chicago Zoological Society, who heads a NOAA panel on unusual mortality events. "In terms of historical numbers, this does stand out as unusual."

Although the stranded calves appear in varied states of decomposition, all of them died within the last few months. Necropsies of six dead calves are underway at the Institute for Marine Mammal Studies (IMMS) in Gulfport, Miss., which will include tests for toxins linked to oil spill.

By Frank Pompa, USA TODAY

"The toxin tests are very important," says Josh Mogerman of the Natural Resources Defense Council environmental group. "The Gulf is a very complicated ecosystem and there are a lot of possible culprits for this, beside the oil spill."

In a typical year, the northern Gulf of Mexico, stretching from Louisiana to the Florida Panhandle, sees two such reports of strandings of underdeveloped bottlenose dolphins (ones less than about 40 inches long), as opposed to the 29 reported as of Wednesday. Counting adults, 48 dolphins of all ages have been reported dead on beaches in the region in the last two months.

State and federal fisheries officials are continuing existing programs that monitor dolphin health, looking for signs of trouble, as well as performing water quality tests that have intensified in the Gulf since last year's oil spill. An increase in beached calves appears to have started last year, two months before the April 20 start of the Deepwater Horizon spill, Rowles says, a reason for caution in linking the deaths to the oil. Other factors that have led to past dolphin deaths include red tides, cold weather, decreases in the dolphin food supply and diseases, Wells says.

"Effects can be cumulative, where animals weakened by chemical exposure face cold weather or some long-term trend that leads to sudden losses among their most vulnerable," he said.

Mogerman notes that some toxicologists have warned that chemicals found in crude oil and in the dispersants used to battle the spill have been linked to reproductive effects in mammals such as dolphins.

Investigators will perform toxicology and genetic tests on the dead dolphin calves. Some bottlenose dolphin populations remain year-round in bays and estuaries in the Gulf, while others travel up and down the coast. If genetic testing reveals the dead calves all belong to one stationary group, then investigators will focus their efforts on finding a cause for the increase in deaths there.