Gulf oil displaced, killed whale sharks?

As an aftermath of one of the largest oil spill accident in the Gulf of Mexico, the feeding habitat of whale sharks has been destroyed, possibly killing some of the world's largest fish, a new research has suggested.

An estimated 4.9 million barrels of oil (one barrel equals 42 gallons, or 159 liters) flowed into an area south of the Mississippi River Delta, where of one-third of all northern Gulf of Mexico whale shark sightings have occurred in recent years, scientists said.

The 45-foot-long (14-meter-long) fish, still largely a mystery to scientists, is considered a vulnerable species by the International Union for Conservation of Nature.

"This spill's impact came at the worst possible time and in the worst possible location for whale sharks," National Geographic News quoted Eric Hoffmayer of the University of Southern Mississippi as saying.

Sightings confirmed that the animals were unable to avoid the slick at the surface, where the giant fish may feed for seven to eight hours a day. The oil may have clogged the fish's gills, suffocating them, or it might have contaminated their prey-though no dead whale sharks have been found, Hoffmayer noted.

"We've seen aerial photos with animals within a few miles of the wellhead and swimming in thick oil.
 
"At the end of the day, if these animals were feeding in an area where there was surface oil, and if they ingested oil, there is a good possibility that they died and sank to the bottom. At this point we have no idea how many animals have been impacted," he said.

For instance, certain toxic ingredients of oil-and even the chemical dispersants used during the cleanup-could potentially cause long-term problems for whale sharks and many other species, scientists noted.

These sharks swim with their wide mouths open to suck in plankton-rich waters, which they then force back out their gills, retaining only tiny morsels of food.

"They would no doubt absorb contaminants even in dispersed form. Does that build up in their tissues and affect their health?" said biologist Bob Hueter of the Center for Shark Research.

To answer that question, many scientists are now searching for the presence of polycyclic aromatic hydrocarbons (PAH) and other oil contaminants in the blood and tissues of Gulf whale sharks.

"It will probably take years to see what the signature of this oil does to the health and physiology of these animals," said Hueter.

But some observations have already suggested the whale sharks have changed some of their habits.

During the summer months following the oil spill, Mote scientists began chronicling repeated near-shore observations of large marine animals, such as whale sharks, that are typically found in far deeper waters out near the eastern Gulf's continental shelf.

"This summer unusually high numbers and species of sharks were here on the West Florida Shelf, and that includes whale sharks in much larger numbers than we are accustomed to seeing," said Hueter.

The team tagged several fish to track their future movements in oiled waters and see whether the disaster causes lifestyle changes in the whales.

One problem is that no one is exactly sure where the bulk of dispersed oil has gone, or in what form it exists.

"In some form or fashion, 60 to a hundred million gallons of oil are still out there, and all we know is it's not at the surface. With this idea of submerged oil out there, we don't know what threats exist to the animals," said Hoffmayer.

For instance, no one knows if the sharks will start to avoid the rich feeding grounds to which the migratory animals have returned regularly so far.

"In coming years we'll hopefully be able to say something about the sightings, either that whale sharks appear to be impacted heavily, or, we were lucky here and they haven't missed a beat," he Hoffmayer.

As scientists learn more about the elusive whale shark, they've already discovered that the impacts of the oil spill disaster could stretch farther than anyone would have suspected just a few years ago.

That's because seemingly disparate whale shark populations ranging from the Caribbean and Central America to the Gulf of Mexico are actually deeply connected, according to Rachel Graham, lead shark scientist with the Wildlife Conservation Society's Ocean Giants Program.

"One of the concerns that I have is that anything that happens to animals in the northern Gulf, where the spill occurred, will have an impact on the larger population in the entire region," said Rachel Graham, lead shark scientist with the Wildlife Conservation Society's Ocean Giants Program.

"It's one large population. And it's at risk because we're only talking about hundreds or perhaps a few thousands of animals in the region-not hundreds of thousands of animals.

 Due to their size, whale sharks require a lot of food to survive, and preferred food such as fish eggs is seasonal and concentrated in a small area-the seas certainly can't sustain millions of these huge animals," she said.