The U.S. National Oceanic and Atmospheric Administration has called the stranding of 123 dolphins on Texas shores from November through March an "unusual mortality event," an official federal listing that allows the agency to access additional funds and set up a team of researchers.
All but four of the dolphins that washed up in Texas were dead, and the few that turned up alive died a short time later, said Blair Mase, the southeast marine mammal stranding network coordinator for NOAA Fisheries. What alarmed scientists though, was the age of the bottle-nosed dolphins that washed up -- juveniles rather than the very young or elderly that normally would be found -- and the fact that Texas had a years-worth of dead dolphins turn up in a five-month period.
The cause, however, may not be known for months, if at all, Mase said.
Complicating matters are an array of things occurring in the Gulf simultaneously, all of which could cause dolphin mortality, Mase said.
To begin with, the Texas coast was plagued during the fall and early winter by a toxic algae bloom called "red tide" that is caused by drought. This past year, the red tide was more severe and lasted longer than usual because of the historic drought that parched Texas and made the estuaries that flow into the Gulf salty and conducive to the algae bloom. Scientists previously have connected "red tide" to dolphin mortality, Mase said, and the strandings in Texas stopped shortly after the bloom ended.
But some of the dolphins washed up underweight, said Heidi Whitehead, state coordinator for the Galveston-based Texas Marine Mammal Stranding Network, a nonprofit organization that is the only authorized stranding network in Texas. Mase said that has not been the pattern for past red tide-related deaths.
Some of the dolphins also were found with discolored teeth and lung infections, prompting researchers to investigate whether they were affected by the same disease found in more than 700 strandings in the northern Gulf, an area stretching from the Texas-Louisiana line east to the Florida Panhandle. Researchers suspect the lung disease may be connected to the millions of gallons (liters) of oil that fouled the Gulf in April 2010 after a well blowout on a BP-operated rig, but have yet to make a final determination, Mase said.
Four of the dolphins found in Texas had a grayish, muddy substance in their stomach. It didn't look or smell like oil, but tests are being run to rule out hydrocarbons. A similar substance was found in some dolphins elsewhere in the Gulf.
"Just like any investigation you don't want to rule anything out," Mase said. "We do know that there is disease out there ... we know that there have been stresses, some due to the BP oil spill, and that could be a reason ... and there is this harmful algae bloom. It could be that it's all of these."
Researchers have conducted more than 30 necropsies so far on the dead dolphins and collected tissue samples, but Whitehead noted one of the difficulties with these investigations is that many of the mammals wash up in late stages of decomposition, leaving little for the researchers to use in their probe.
To date, NOAA has declared five "unusual mortality events" in Texas, all involving bottle-nosed dolphins, and has only determined a cause -- morbillivirus infection -- for an event in 1994. There have been 19 marine mammal events in the entire Gulf of Mexico and 56 in all US waters since 1991.