Popular sushi fish at risk of overfishing

Despite the going rate of over $40,000 per fish, the Atlantic bluefin tuna — one the most highly evolved fish species — is in immediate danger because of overfishing.

Professor Joseph E. Powers of Louisiana State University gave a lecture on the marine animal on Tuesday at the School of Forestry and Environmental Studies. It was the first in a lecture series that supplements the class “The Future of Fisheries — Over-Harvested or Sustainably Managed?”

Powers’ talk introduced the basic techniques and terminology of fishery assessment and management, focusing on how they can be applied to the Atlantic bluefin tuna. He explained key concepts such as biomass sustainable yield, which is the largest yield that can be taken from a species’ stock over time, and total allowable catch, which is a set quota of fish that can be taken from a fish stock each year.

The challenge in his work, Powers said, was fitting mathematical models and charts to the sometimes “imperfect data.”

“You try to fit the best model to the observations you have,” he said.

Powers spent a good deal of time highlighting the differences between the bluefin tuna stocks in the Eastern Atlantic Ocean and the stocks in Western Atlantic Ocean and the Mediterranean Sea. According to Powers, there has been long-standing debate about the mixing and movement of these two stocks, but the current consensus is that there are indeed two main breeding populations which do have some interactions.

In the future, he predicts tuna populations will be evaluated in smaller subsections of oceans rather than in two vast areas, as management strategies will likely have to be formulated based on smaller regions.

The lecture also touched on what makes Atlantic bluefin tuna so vulnerable. Compared to other fish, the bluefin take a relatively long time to reach maturity and grow slowly as juveniles. Because of their slow growth rates, it takes longer to detect population changes and to identify overfishing, which Powers said exacerbates the danger to this species.

Atlantic bluefin tuna are also notable because of their incredibly high market value, which is largely driven by the demand for bluefin tuna sushi.

“The major reason it’s difficult to deal with the Atlantic bluefin is that it becomes a question of would you like this fish or a new car,” Powers said.

Indeed, bluefin tuna have been known to fetch prices of $40,000 and higher per fish, particularly in the key market of Japan.

The prospects for the possible recovery of Atlantic bluefin tuna look grim, at least according to Powers. Currently, the United States is not able to find enough fish to meet its relatively low yearly catch quota, leading some to suggest that the Eastern Atlantic stocks have alerady been greatly depleted. The stocks in the Western Atlantic and Mediterranean are not much better off, and the European Union — which is trying to expand catch quotas — is currently combating various NGOs that promote conservation.

Much can be lost in the political shuffle, Powers said.

“The actual recovery to [biomass sustainable yield] is going to take 20 to 30 years under the best circumstances,” Powers said. “I’m optimistic to a degree about meaningful regulation in the next five years, but demand for these fish means in 50 years it will be difficult.”

The majority of the more than 60 attendees at the lecture were students in the fisheries class or faculty at the school. Sean Dixon FES ’09, who has worked on a fishing boat, said the lecture provided “a good perspective on the east-west stock debate in a very detailed way.”

Jude Wu FES ’09 agreed, adding that she felt conflicted after the talk.

“On one hand it made me really want to get some sushi, but on the other hand I realize I can’t eat it ever again without thinking about the effect it’s having,” she said.

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