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How the BP Oil Spill Will Affect Bluefin Tuna

  • Spence Cooper
  • July 5, 2010

In the past 40 years, Bluefin tuna populations have declined by 80 percent due to industrialized overfishing. In April, Barbara Block, a Stanford University marine biologist noted that the giant bluefin only show up for about a month to spawn, and April is the time they show up. Block says many of the tuna go exactly to the region where the Deepwater spill is centered because it’s one of the preferred breeding areas.

Block and her colleagues have been tracking bluefin tuna with small devices since 1996 through a project called Tag-a-Giant (TAG). With TAG, Block determined that the tuna regularly return to spawn in the Gulf at this time every year.

“The population has declined 80 percent to 90 percent of what its original spawning biomass was,” Block said. “But recent efforts to have the bluefin categorized as an endangered species failed. Now, just when you need it to have a nice spring so that it can spawn, you have this accident.”

Bluefin are attracted to eddies that are favorable for spawning. The Gulf eddies are above an area where the long, flat continental shelf extends out from the Louisiana coast, then drops where warm currents flood in, and bump into the shelf. Unfortunately, this also happens to be prime area for oil exploration and drilling.

“There is a much larger disaster unfolding here environmentally than people realize,” said Block. “There is a lot of focus on the Louisiana shoreline, but this is America’s greatest fisheries nursery, and we’ve got to pay attention to what’s going on immediately.”

What is particularly troublesome are the warnings from scientists — before the oil spill — about the collapse of the Gulf of Mexico-spawned bluefin stock. Despite these warnings, the US has continued to allow fishing in the region.

And the threat to bluefin survival extends beyond the Gulf. Paul Greenberg, author of “Four Fish: The Future of the Last Wild Food”– which will be published next month by Penguin Press — notes that “catches from the high seas have risen by 700 percent in the last half-century, and much of that increase is tuna. Moreover, because tuna cross so many boundaries, even when tuna do leave the high seas and tarry in any one nation’s territorial waters (as Atlantic bluefin usually do), they remain under the foggy international jurisdiction of poorly enforced tuna treaties.”

And just when you think you’ve learned the worse, USM, Tulane scientists now say oil in Gulf of Mexico has infiltrated into the sea food chain itself.

Scientists at The University of Southern Mississippi and Tulane University have found oil in the postlarvae of blue crabs entering coastal marshes along the Gulf Coast signaling that oil may be entering estuarine food chains.

The Mississippi Sun Herald reports that the director of the Center for Fisheries Research and Development at the Gulf Coast Research Laboratory, Harriet Perry, has found droplets of hydrocarbons or oil, in blue crab and fiddler crab larvae. According to Perry, the oil appears to be trapped between the hard, outer shell of the crab and its inner skin.

“I’ve been sampling in Mississippi coastal waters for 42 years and I have never seen this,”declared Perry. “My guess is that the crab picked up this oil offshore while in the megalopal (postlarval) stage and brought the oil with it when it came back to the marsh.”

Blue crabs are a favorite food of a host of fish species that live in the marsh. “Speckled trout and red fish feed heavily on the crustaceans. The food chain is now affected because whatever eats the crab will be affected, and so on.”

Perry’s group has also spotted small fish with oil clinging to their bodies. “Oil on the fins decreases mobility and makes these fish easy prey for other species. This is yet another example of oil being incorporated into the food chain,”she added.

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