The BP Oil Spill's Long-Term Threat to Bluefin Tuna

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Bluefin tunaWhen BP's Deepwater Horizon oil spill spewed millions of gallons of crude into the Gulf of Mexico, one of the most pressing questions was how the environmental disaster would affect the area's other major industry: fishing, and in particular, the highly prized bluefin tuna.

In the short term, Gulf fishing was crippled, as thousands of square miles were immediately closed. But even after some of these areas reopened, scientists and fishermen alike worried about the long-term effect of contamination on the area's bountiful aquatic life. Recently, evidence has emerged to suggest that the oil spill may have an impact far beyond the Gulf, threatening one of the world's most lucrative fishing species.

The controversy surrounds dispersants, the chemical compounds that BP (BP) used to break up the spilled oil. Basically a form of detergent, dispersants make it possible for oil to interact with water, transforming huge oil slicks into microscopic droplets that could seemingly disappear into the Gulf. In theory, at least, this would make it easier for bacteria and weather to further break down the oil, allowing it to dissolve into the environment.

Ignoring a Key Issue?

When BP began using dispersants, many environmentalists fretted that the compounds might harm the area's fragile ecosystem. In response, the U.S. Environmental Protection Agency launched a two-pronged study to measure the toxicity of various dispersants. Their ultimate conclusion was that the eight dispersants tested -- including Corexit 9500A, the main compound used in the Gulf -- were generally less toxic than crude oil. What's more, the EPA detected little or no increase in toxicity when dispersants were combined with oil. That is, the action of breaking down an oil slick generally did not add more toxins to the Gulf.

According to Peter Hodson, an aquatic toxicologist at Queen's University in Kingston, Ontario, the EPA study ignored a key issue. While dispersants don't increase the toxicity of petroleum, they can vastly increase the chances that a fish will interact with oil, and that the oil's toxicity will affect sea life.

"After all," Hodson points out, "Oil toxicity isn't an issue until fish are exposed to it. Unfortunately, as minuscule dispersed oil droplets combine with water, the volume of the oil spill vastly expands. This can increase the risk to fish by 100- to 1,000-fold."

Out of Sight, Out of Mind

One of the big problems, Hodson notes, is a matter of perspective. While oil dispersants make a spill disappear from the water's surface, they don't actually make it go away. For people, who naturally view a spill from above the surface of the water, it's easy to see the effect of oil on birds, people and beaches, but harder to see the effect on fishes and other underwater organisms. That effect that may be increased as dispersants cause oil to combine with the water instead of float on the surface.

Hodson emphasizes that "This can lead to a blind approach when assessing risk, a process that is already difficult in an oil spill. If you are convinced that dispersants are not an issue because they aren't more toxic than oil, then a lot less attention will be paid to what's under the water, and we're a lot more likely to endanger aquatic resources."

This is particularly problematic for the Gulf's sea life, especially eggs and embryos, which, Hodson says, "can't move out of the way of oil." Consequently, they're likely to absorb dispersed oil and the chemicals that it releases. To make things worse, Hodson continues, "embryos and baby fish have thin skins, which makes them more susceptible to chemical contamination. This can lead to 'teratogenic effects,' or deformities."

Bluefin Tuna in the Crosshairs

For the most part, attention has focused on the oysters and shrimp for which the Gulf is known. However, its waters are also home to a wide variety of sea life, including northern bluefin tuna, one of the most expensive fish species in the world. The tuna, which conservationists claim is on track to become an endangered species, spawns in only two areas: the Mediterranean Sea and the Gulf of Mexico.

While many fish may die because of the contamination, an even bigger problem may be the long-term impact on bluefin breeding. Hodson notes that "petroleum contamination could cause embryos to develop deformities, which can make it impossible for the young fish to grow old enough to reproduce." This, in turn, could leave a major hole in breeding populations over the next few years.

To make things worse, bluefin tuna is already experiencing major problems. Exceedingly popular for sushi, the price of bluefin has skyrocketed over the past few years: In January 2010, a 510-pound bluefin tuna sold in Tokyo's fish market for $175,000. With prices like that, fishermen are eager to reel in the fish.

Hammered at Both Ends

Fearing the bluefin's extinction, the International Commission for the Conservation of Atlantic Tuna set a 2010 quota of 13,500 tons, a 38% drop from 2009. In some regard, however, the ICCAT's quota is largely irrelevant: Because of poaching and overfishing, the actual annual tuna yield is likely closer to 60,000 tons.

With so much money on the line, the pressure is tremendous to keep the bluefin tuna industry chugging along. Last month, fishing advocates successfully tabled a European Union plan to radically cut quotas aimed at allowing bluefin stocks to recover. Meanwhile, U.N. attempts to scale back or limit the industry have been blocked by several countries, notably Japan, which has lobbied aggressively to keep fishing quotas high.

Unfortunately, it will likely be years before scientists can fully measure the impact of the BP spill on the fish. During the initial cleanup efforts, it was impossible to directly observe the effect of the Deepwater Horizon oil on bluefin tuna embryos, though Hodson emphasizes that the long-term effect will be a decline in breeding stocks.

However, he warns, with overfishing threatening older bluefin tuna and oil contamination threatening embryos, humans are "hammering the bluefin population at both ends," a process that is likely to lead to a devastating conclusion.

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