What is killing the dolphins in the Gulf of Mexico?

Strandings — when dolphins or other marine mammals wash up onshore, either dead or alive — are occurring at “unusual” rates in the Gulf of Mexico, worrying scientists.

From February 2010 to June 17 there have been 757 dolphin and whale strandings in the northern Gulf of Mexico, according to the U.S. National Oceanic and Atmospheric Administration (NOAA). Five per cent of the mammals stranded alive, while 95 per cent stranded dead, the federal agency reports.

Although the strandings have occurred over a period of more than two years, scientists are treating them as one event.

“This is one of our longest. . . mortality events that we have ever dealt with,” says Blair Mase, NOAA’s southeast regional marine mammal stranding co-ordinator, “and it is still ongoing.”

The strandings span the northern Gulf, including the Louisiana/Texas border, Mississippi, Alabama and the Florida panhandle. Under NOAA’s Marine Mammal Protection Act, an “unusual mortality event” — when a stranding occurs unexpectedly and involves a significant die-off — has been declared.

There has been a similar series of strandings off the Texas coast, where 123 bottlenose dolphins have washed ashore from November 2011 to March 2012. An unusual mortality event was again declared.

While the Texas strandings coincide with a harmful algal bloom of the toxin Karenia brevis — better known as red tide — the exact cause of the massive die-offs hasn’t been determined, says Mase.

POSSIBLE CAUSES

Normal strandings occur year-round in the Gulf, with an average of two to six per month, Mase says.

In the past, typical causes have included infectious diseases, biotoxins released from algae blooms, boat strikes and fishery entanglements.

What is surprising now is the number of dolphins dying.

Mase expects it could take a year to know the cause(s).

“It’s too early. We don’t have all the information. . . the information that is coming in right now is just insufficient to make any direct causes here,” she says.

Four of the 123 dolphins in the Texas event were found alive. While investigations continue, NOAA’s preliminary findings of the deceased animals include poor body condition, teeth discoloration and lung infections. A blackish-grey, mud-like substance was found in the stomachs of four of the animals.

Eighteen unusual mortality events have occurred in the Gulf since 1991 and there have been a total of 56 declared in U.S. waters since then, the agency reports.

BP OIL SPILL

NOAA scientists are looking at all possible causes for both current stranding events, including if they are related the April 2010 BP oil spill. Blood and tissue samples are being analyzed, Mase says.

So far, 12 of the dolphins in the Gulf have tested positive for Brucellosis, a bacterial infection that causes aborted fetuses.

“We don’t know what that really means. We don’t know if it’s in the Gulf and maybe these animals were more susceptible because of their environmental stressors going on. . . one of their environmental stressors could’ve been the impact of the BP oil spill,” Mase says. “That’s one of the working theories that we’re looking into right now.”

The Deepwater Horizon drilling rig exploded on April 20. It sunk two days later, spilling 4.9 million barrels of crude oil into the water before it was capped.

“I think it is important also to realize that there could be multiple issues here,” Mase says.

Original Article
Source: the star
Author: Lorianna De Giorgio