Federal scientists trying to figure out why dolphin deaths along the Gulf of Mexico are up this year now have a second challenge: a sharp jump in sea turtle deaths in some Gulf areas.
"In the past couple of weeks, we've seen an increase" in turtle deaths in the northern Gulf, Connie Barclay, a spokeswoman for the National Oceanic and Atmospheric Administration, told msnbc.com.
Since March 15, she noted, 39 deaths were confirmed in Mississippi, 4 in Alabama and 3 in Louisiana.
"The spring time is the typical time when turtle strandings in this region begin to increase," Barclay added, "but the sharp increases in recent days are of concern."
"Tests will be done for biotoxins, such as those from harmful algae blooms, which are common in the Gulf," she said, and NOAA is contacting states to see if fishermen are accidentally hooking sea turtles.
"All causes of death, including petroleum, will be investigated when possible, based on decomposition," she added, and "all turtles are being carefully examined for signs of external oiling."
Some 400 sea turtle deaths were reported in the five months after the BP oil spill last April, but the number dropped off sharply starting in October. All seven species of sea turtles are listed under the Endangered Species Act.
The news comes as the mystery behind the dolphin deaths grew to include a sense of intrigue: NOAA is keeping a tight lid on its ongoing probe into the deaths, which are possibly connected to the BP spill, causing tension with some independent scientists.
In the case of dolphins, biologists hired by the National Marine Fisheries Service, a branch of NOAA, to collect specimens and tissue samples were quietly told late last month to keep their findings confidential.
The order was in a Fisheries Service letter informing outside scientists that its review of the dolphin die-off, classified as an "unusual mortality event (UME)," had been folded into a federal criminal investigation of the oil spill.
"Because of the seriousness of the legal case, no data or findings may be released, presented or discussed outside the UME investigative team without prior approval," said the letter, obtained by Reuters.
The Fisheries Service "did not issue a gag order," Blair Mase, the agency's stranding coordinator for the Southeast, told msnbc.com in response to the disclosure. "We did ask partners" to refrain from releasing data so as "to ensure confidentiality."
Still, a number of partner scientists said they have been personally rebuked by federal officials for "speaking out of turn" to the media about efforts to determine the cause of some 136 dolphin deaths this year in the Gulf, and 115 others last year after the April spill.
Moreover, they said collected samples and specimens are being turned over to the government for analysis under a protocol that will leave independent scientists in the dark about the efficacy and outcome of any lab tests.
Some partner researchers in the agency's Marine Mammal Stranding Network complained such constraints undermine the transparency of a process normally open to review by the scientific community.
"It throws accountability right out the window," one biologist involved in tracking dolphin deaths for more than 20 years told Reuters on condition of anonymity. "We are confused and ... we are angry because they claim they want teamwork, but at the same time they are leaving the marine experts out of the loop completely."
Some question why the Fisheries Service has taken so long to get samples into laboratories.
"It is surprising that it has been almost a full year since the spill, and they still haven't selected labs for this kind of work," said Ruth Carmichael, who studies marine mammals at the independent Dauphin Island Sea Lab in Alabama.
"I can only hope that this process is a good thing. I just don't know. This is an unfortunate situation."
Mase, a marine mammal scientist, said lab results would go directly back to the Fisheries Service, and hopefully in about two to three months.
"We have to be very methodical," Mase said. "The criminal investigation does play a role in the delay of findings, but it has to be done this way."
For Mase and others, this is the first time their work on marine mammals has become part of a potential crime scene.
"This is all new to pretty much all of us," she said, adding that "we're not sure how that's going to work" when asked if the results would be released to the public before any criminal action.
As of Monday night, scientists counted 136 bottlenose dolphin carcasses found since mid-January along the shores of Louisiana, Mississippi, Alabama and Florida, almost half of them newly born or stillborn infants.
And Mase noted that "we're still in the response phase" since carcasses are washing up daily, including at least two on Tuesday in Louisiana.
The tally so far this year, which compares to 31 deaths on average during the same time of year between 2002 and 2009, coincides with the first dolphin calving season in the northern Gulf since BP's Deepwater Horizon drilling rig exploded last April.
The blast killed 11 workers and ruptured a wellhead on the sea floor, dumping an estimated 206 million gallons of oil into the Gulf over more than three months.
Last year, 115 dead dolphins, most of them adults, washed up along the Gulf Coast in the weeks and months following the blowout.
But Mase pointed out that even before the spill started in late April, a jump in dolphin deaths was seen in February and March of 2010.
The latest spike in deaths, and high concentration of premature infants among them, has led some experts to speculate that oil ingested or inhaled by dolphins during the spill has taken a belated toll on the animals, possibly leading to a wave of dolphin miscarriages.Story: Ocean currents keep dolphin populations apart
But most of the specimens collected bear no obvious signs of oil contamination, making lab analysis crucial to understanding what caused the deaths.
Mase said the carcasses also are considered potential evidence in the natural resources damage assessment being conducted in conjunction with civil litigation pursued against BP by the government simultaneously with the criminal probe.
"It is frustrating at times," she said of the slow process, "but you have to understand the big picture. If there is a responsible party we want to make them responsible."
Msnbc.com's Miguel Llanos and Reuters contributed to this report.