Scientists: Gulf oil spill threatens breeding ground for bluefin tuna

McClatchy NewspapersJune 18, 2010 

WASHINGTON — Near the end of a 12-day cruise in the Gulf of Mexico to study the habitat of just-hatched Atlantic bluefin tuna, scientist Jim Franks came upon fields of oil sheen as far as he could see.

Mixed with the oil were large amounts of sargassum, the golden brown alga that drifts at the whim of winds and tides and shelters the quarter-inch-long bluefin tuna larvae.

How the young will fare and what will happen to the population of bluefin tuna will affect a wide range of people, including the tuna fishermen of Gloucester, Mass., for whom a single fish can fetch $20,000 or more, and sushi chefs everywhere.

While his research is still incomplete, Franks fears that the gushing BP oil will be trouble for Atlantic bluefin tuna. The fish can grow to 1,500 pounds — as large as a Volkswagen Beetle — but their numbers have greatly declined because they fetch such high prices for sushi and sashimi.

The sargassum and the warm waters of the Gulf of Mexico are an important nursery and habitat not only for these fish but also for whales, sharks, and other big ocean fish such marlin and swordfish. What happens to these top predators will be one important part of measuring the costs of the oil spill to the environment.

Atlantic bluefin tuna spawn in just two places: the Gulf of Mexico and the Mediterranean Sea, and in the Gulf, they spawn in April and May.

Franks said it's possible that adults might avoid the oil and spawn away from it, but that currents would carry their young into it. "It's still speculation on my part, but based on where we collected larvae and the current flows, some would appear to have drifted into the oil," he said.

Greg Stunz, a marine scientist at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University, said that young bluefin tuna are the most vulnerable.

"Most adults will have or will be moving back to the Atlantic by now, but the larvae and young juveniles will remain and have to deal with the impacts of the oil," he said. "I can't image a small bluefin tuna could handle oil, dispersants, and associated chemicals very well, but we have limited scientific data to tell us how bad it may be."

Still, he said, "given the tremendous overfishing occurring on this majestic species, the spill impact may represent a very serious blow to Gulf populations of bluefin tuna. Will they recover and exactly what those impacts may be are unknown at this time, but most scientists are very concerned."

Franks and his team from the University of Southern Mississippi were in the right place — near the Deepwater Horizon spill site — and at the right time — during the brief period when the larvae are at the surface, before they quickly grow into juveniles and disappear into deeper waters — to collect data that may help answer questions about the effects of the oil on the future of Atlantic bluefin tuna.

The results will come after hours studying samples.

Fishing for Atlantic bluefin tuna has been banned in the Gulf of Mexico since the 1980s, but it's allowed elsewhere.

Understanding the effects of oil on all these species will depend largely on work conducted or funded by the National Oceanic and Atmospheric Administration. NOAA in the past month has sent some of its research vessels into the Gulf, and it also supports independent researchers, including Franks and his colleagues.

Scientists think there could be some good news for the Atlantic bluefin tuna.

Most of the spawning normally takes place farther west in the Gulf, where the oil hasn't reached. Even so, the peak spawning period coincided with the BP blowout, and it's not clear whether the young fish, which are very difficult to track, will move into the oil.

The fish also could be at risk if they eat contaminated prey or if the oil coats their gills. Researchers also say that during the recent spawning season, chemical dispersants could have been toxic to the eggs.

Scientists are preparing themselves for much research ahead on the effects of the oil on the bluefin tuna and other species.

"We'd like to get started as soon as possible, but it's all dependent on the funding. Research vessels are very expensive." Franks said in an interview after he returned to the Gulf Coast Research Laboratory in Ocean Springs, Miss.

His team's trip on the lab's 95-foot research ship, the Tommy Munro, had been funded by NOAA before the spill. When the vessel entered oily water, it took a few samples, and so researchers will be able to compare them with samples taken from clean areas.

Monica Allen, a NOAA fisheries spokeswoman, said that its scientists also collected samples of bluefin tuna larvae in early May, but it's not clear whether they got any from oiled waters because the vessel wasn't certified to work in the spill area. Since then, the NOAA ship Gordon Gunter has taken samples in the spill area of fish larvae, but it's not yet known if any were bluefin tuna.

Another NOAA ship, the Delaware, was headed to the Gulf to test swordfish, yellowfin tuna and other migratory species for traces of oil and chemical dispersants. The NOAA ships Thomas Jefferson and Pisces also are in the Gulf to study the impact of the spill.

NOAA scientists also put tags on four adult bluefin tuna that will allow them to monitor the fish via satellite.

Barbara Block, a professor of marine sciences at Stanford University, and her colleagues have tagged many Atlantic bluefin tuna over the years with these satellite communication devices.

Block also has applied advances in gene studies in modern medicine to learn more about the physical conditions of the fish. These 21st century tools are now available for use in the Gulf of Mexico, she said.

ON THE WEB

Photos and audio of Jim Franks' calls from the research cruise of the Tommy Munro

Information about spawning bluefin tuna and the oil spill from Barbara Block and the Tag-a-Giant Foundation

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