PASCAGOULA, Miss. (AP) - Dolphins in the Mississippi Sound from western Horn Island to eastern Petit Bois Island have been photographed since the summer of 2010 as part of the assessment of damages from the Deepwater Horizon oil spill.
On Wednesday, representatives from the National Oceanic and Atmospheric Administration and the Mississippi Department of Environmental Quality demonstrated how the on-the-water portion of the bottlenose dolphins study has been conducted.
In a separate study, skin and blubber samples have been collected from dolphins.
NOAA spokesman Tim Zink said, "What we are doing here is building a database. The dorsal fin on a dolphin is a unique identifier. It is like a fingerprint. We go out and photograph the dorsal fins of these dolphins and then build a database that helps us understand where they live, where they travel."
The photos give the dolphins an identity.
"We know if we are suddenly not seeing dolphins in a place that they should be that we may have a problem on our hands or if we find them dead we know where they lived," Zink said.
The study of dorsal fin photos and biopsy samples are part of the Natural Resource Damage Assessment process, he said.
Dolphin deaths also are being investigated as part of an "unusual mortality event" in which more than 700 dolphins have died since February 2010.
"The unusual mortality event investigation began two months before the oil spill, and it has been a rare event in that we have never seen an unusual mortality event investigation last as long or involve so many dolphins.
"We can't definitely say the oil spill played a role or contributed to that, but it is one of the likely causes that we are investigating very closely," Zink said.
Keith Mullin, a research biologist with NOAA's National Marine Fisheries Service, said the dorsal fin and biopsy studies have focused on the Mississippi Sound, Chandeleur Sound and Barataria Bay in Louisiana.
"We want to see how abundance changes or doesn't change over the study period," Mullin said. "We can also make estimates of survival."
The dorsal fin study also should yield information about reproduction, he said.
The tissue samples are tested for DNA and evidence of hydrocarbons, he said.
Mullin said there is no official estimate on the number of dolphins in the Mississippi Sound study area, but he estimated "well over a thousand dolphins use that area."
Dolphins are an indicator of the ecosystem's health, the said.
"They are top level predators," he said. "In order for there to be top level predators, the rest of the ecosystem has to be functioning well."
Richard Harrell, director of MDEQ's Office of Pollution Control, said the damage assessment process will likely take years if not decades to complete.
"We've got documentation of oil exposure," Harrell said. "We've got documentation of dolphins swimming through oil that came ashore. They definitely got exposure. The challenge now is showing the nexus of injury. What is the injury to the dolphins and how much that injury may be."
The goal of the damage process is to determine the damages, what restoration projects are needed and the compensation to public for the lost use of resources, he said.
A preliminary finding of 32 dolphins captured in Louisiana's Barataria Bay found them "very sick."
The dolphins were captured in August 2011 and found to suffer anemia, low body weight, hormone deficiencies, liver disease and lung problems.
Barataria Bay was heavily oiled during the spill.
"In a nutshell, those findings are a bit scary," Zink said. "We are finding some very sick dolphins."
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