Deepwater Sharks May Hold Answer to Oil-Contaminated Seafood
As tainted fishing areas reopen, scientists think big to assess oil contamination in Gulf seafood
A week after the explosion that began the Gulf oil disaster, Louisiana officials closed areas of state waters to fishing, including the harvest of finfish, shrimp, crabs, and oysters. A day later, NOAA announced the closure of an area in federal waters.
By June 1, 2010, more than 61,000 square miles, about 25 percent, of federal waters in the Gulf of Mexico were closed to commercial and recreational fishing. Three weeks later, the total closed area came to nearly 87,000 square miles, or about 36 percent of the U.S. economic zone in the Gulf. State waters from Louisiana to parts of Florida’s Panhandle were also closed.
Then, as NOAA and state agencies ramped up their seafood testing programs, fishing areas were reopened. Today, all state waters along the Gulf coast are open to commercial and recreational fishing, and only one area in federal waters remains closed: a thousand square mile area around the Deepwater Horizon wellhead (closed “until further notice”).
State and federal agencies are pretty sure Gulf seafood is safe to eat. But some organizations think government officials might be playing fast and loose with food safety to get people back to work, because many of these same state and federal agencies directly control the ability of tens of thousands of people to make a living in seafood and seafood-related industries.
As Natural Resources Defense Council senior scientist Dr. Gina Solomon wrote, “I took a look at the data on which NOAA based their decision [to reopen shrimping areas in September] and was surprised to find that their data included only 12 samples of shrimp, consisting of a grand total of 73 individual shrimp, caught from an area about the size of the State of Connecticut. Does that reassure you that they've really found whatever contamination might be out there?”
Too Many Shrimp in the Sea
Well, instead of testing all the shrimp, why not examine animals along the food chain, starting with finfish that feed on shrimp and finishing with large sharks that eat the shrimp-fed finfish? If shrimp have been contaminated by harmful chemical products or residue from the BP oil well, it’s likely those poisons can be traced through the food chain.
Enter Dr. Dean Grubbs of Florida State University’s Coastal and Marine Laboratory in St. Teresa, Fla.
Grubbs, a marine ecologist whose earlier work led to creation of a federal Habitat Area of Particular Concern for juvenile sandbar sharks in the lower Chesapeake Bay, is assessing the exposure of deepwater fish to oil-based pollutants. He’s focusing on dogfish sharks (Squalidae), gulper sharks (Centrophoridae), cow sharks (Hexanchidae), cutthroat eels (Synaphobranchidae), and cusk eels (ophidiiformes).
“Most people don’t realize that 56 percent of all shark species in the world live their whole lives below 700 feet deep,” said Grubbs. “And most don’t get bigger than this [holds his hands about two feet apart]. And only about 0.1 percent of all papers published on sharks are on those deepwater species. We don’t even know what’s down there,” he added.
Grubbs’ team will take liver, bile and muscle samples from sharks and other fish caught at depths from about 650 feet to more than 6,500 feet.
The samples will be analyzed by Dr. Jim Gelsleichter of the University of North Florida, who specializes in the effects of environmental pollutants on sharks and rays. In particular, Gelsleichter will be looking for evidence of hydrocarbons.
Sampling will start at the Madison-Swanson Reserve, near the edge of the continental shelf, and follow a transect to DeSoto Canyon, a steep-sided chasm about 185 miles south of Pensacola, Fla. The canyon extends to a point barely 40 miles from Panama City Beach.
A research cruise last summer led by biogeochemist Dr. David Hollander, of the University of South Florida, found BP’s oil on the floor of DeSoto Canyon and a plume in the nearby water column. Hollander also found oil in plankton, the base of the marine food chain.
The Proof is in the Prey
“A lot of sharks vertically migrate, or at least migrate up slopes,” said Grubbs, which means the sharks’ feeding patterns put them and their prey in areas potentially impacted by oil and dispersants.
Grubbs has satellite-tagged dozens of sharks, including many bluntnose sixgill sharks, one of the largest of the deepwater species. “What we found is that the sixgill sharks have this beautiful diel [24-hour] pattern of migration. In Hawaii, we find them up around 200 meters at night. As soon as the sun rises they drop down to about 600 meters, then as soon as the sun sets they come back to 200 meters. And every day they do that. In the Bahamas they were doing it at about 400-1,100 meters. In Virginia, from about 100-300 meters,” he said.
From the side, the pattern looks like a flat-bottomed letter “U.” Some sharks follow the steep slopes of their habitat while others exhibit the pattern in the open water column.
“The reason most of these fish migrate is that there’s a whole mesopelagic boundary community [depths from about 650 to 3,300 feet] that does that exact same vertical migration,” said Grubbs. “Shrimp and lantern fishes, small sharks and lots of squid. The small sharks are feeding on these animals and, of course, the big sharks are feeding on the smaller sharks and fish, so the whole food chain is translated up this mesopelagic community.”
“If the lab finds oil, it would come from diet, not from oil stuck to gills. That could be the indicator that other species were contaminated,” said Grubbs.