Whale Sharks Feast on Tunny in Oil

“I would be concerned about the sub-lethal effects on whale sharks of consuming or being exposed to that much oil”

12-22-2010 // Bob Serata

A week after discovering the largest aggregation of whale sharks on record — more than 100 fish — Dr. Eric Hoffmayer, assistant research scientist and resident whale shark expert at the Gulf Coast Research Laboratory in Ocean Springs, Miss., got the bad news that at least three others had been seen and photographed swimming through “streamers” of crude oil four miles from the Deepwater Horizon wellhead site.

Hoffmayer, along with dozens of other scientists around the Gulf, had been counting on the whale shark’s ability to smell or sense oil in the water and, so, avoid it.

Whale sharks cruise along the surface with their mouths open, scooping in sea water, then filtering out and eating plankton, fish eggs, larvae and juvenile marine animals. This summer they probably sucked in some mouthfuls of crude oil and Corexit-treated oil.

Oil sticks to their gills, making it difficult, if not impossible, for whale sharks to take oxygen from sea water. They suffocate.

How Many Whale Sharks Died During the Oil Disaster?

Of the about 100 marine mammals that were recovered dead after the Gulf oil disaster, no dead whale sharks were recovered. How many actually died from oil exposure will likely remain a mystery, as it’s unlikely they will be found. When whale sharks die, they sink (as true sharks, they have no air bladders). And when a few thousand pounds of dead meat hits the sea floor it doesn’t last long — it provides life-giving food to dozens of species of fish and crustaceans.

Scientists hope the whale sharks didn’t ingest an oil-and-Corexit cocktail by directly swallowing the stuff or ingesting contaminated sea creatures.

“What we’ve found by sampling plankton under large aggregations of whale sharks in the last three or four years is that at every one of those locations the primary prey was fish eggs,” said Hoffmayer. “We’ve been able to genetically ID the eggs and in every encounter there was the same species that was spawning: little tunny [aka false albacore],” he said.

Hoffmayer also found that whale sharks travel long distances to find little tunny eggs.

“I’ve analyzed eggs from samples taken in Mexico where they get these large aggregations of feeding whale sharks and it was little tunny as well,” he said.

“Whale sharks are solitary, but they do aggregate to feed,” said Hoffmayer. “We still don’t understand how they’re sensing the food and how they know to show up for something like a specific fish spawning event that lasts about 12 hours. How do 100 animals know exactly when and where to show up?”

There’s a growing body of evidence showing whale sharks visit connected seas and return to previously-visited areas.

In August 2009 a satellite tagged whale shark’s signal was picked up in the East Flower Garden Banks National Marine Sanctuary off of the Texas coast. It had been tagged off Quintana Roo, Mexico in July 2008, a straight-line distance of more than 660 miles.

Another whale shark was photo-identified off Belize in April 2003. It was photo identified in the same area in 2005, then identified off Pensacola, Fla. in July and August 2009.

Still another whale shark was photo identified in Utila, Honduras in 2002, 2006 and 2007, then off the Florida coast in August 2009.

Hoffmayer added, “We’ve had one of the sharks from the aggregation of 100 get photographed off Isla Mujeres, Mexico in September, which demonstrates that animals that were potentially exposed are not staying in the region and the effects will most likely be far reaching for this large, highly migratory species.”

So, will oil- or dispersant-sickened whale sharks be visiting the southern Gulf or Caribbean or even the western Atlantic? Will their reproductive habits, about which little is known, be affected? And what about the effects BP oil and dispersants had or will have on little tunny populations — what are the long term consequences for whale sharks?

“I would be concerned about the sub-lethal effects on whale sharks of consuming or being exposed to that much oil,” said Dr. Bruce Stein, National Wildlife Federation's associate director of wildlife conservation and global warming. “Given their method of feeding, filtering large quantities of water, if the data shows they were moving through the spill zone [it does] you know they were exposed to hydrocarbons.”

That’s part of Hoffmayer’s plan, too. But until new funding appears, he’s in the same boat (you should excuse the pun) as so many other marine scientists. Lots of questions, lots of motivation and brain power, few resources.

“We need to do more tagging,” said Hoffmayer. “From day one [of the oil spill] the offshore pelagic environment was impacted. We’ve got to get a better understanding, not just of individual animals but of populations. We need to answer the habitat needs questions, find out how important the Northern Gulf habitat is to these species,” he said.

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