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Grammar snobs will tell you the term "jumbo shrimp" is an oxymoron. But as this ScienCentral News video reports, ocean scientists studying shrimp in the Gulf of Mexico are concerned the term could become obsolete.
"Shrimp size in the Gulf of Mexico has declined over the past 10 or 15 years, about I think it's 15 or 20 percent," says to Larry Crowder, professor of marine biology at Duke University Marine Lab. "This is important to shrimpers because shrimp are sold by weight, but also by size-class. And if you go to the store to buy shrimp, if you buy the jumbo shrimp they cost more per pound than if you buy the teeny shrimp." Crowder says the problem starts on farms in the 31 states with rivers that feed into the Mississippi. Nitrogen from fertilizer runs off the farms and into these rivers and eventually empties into the Gulf of Mexico. "The nitrogen stimulates production of algae in the Gulf of Mexico, and to the degree that that algae isn't used up in the food web, it falls to the bottom and decomposes," says Crowder. "While it's decomposing, bacteria use oxygen in that decomposition process. So the nutrients enhance algal production, which subsequently leads to low oxygen in the bottom of the Gulf of Mexico."
image: Florida Dept. of Agriculture
When enough oxygen gets sucked out of the area, it becomes a "dead zone" where nothing can survive. The current dead zone in the Gulf was discovered in 1974, and over the years has grown to some 7,000 square miles, or about the size of New Jersey. What's worst for the shrimp is where the dead zone is located.
"We can go back to maps that were generated from fisheries data in the 1950s and 1960s which show the area of the Gulf of Mexico that's now the dead zone was in fact the most productive fishing grounds for shrimp and fishes in the Gulf of Mexico in the 1950s and 1960s," says Crowder.
So the shrimp had to move to healthier waters. But the problem is that it seems the different temperatures of those new waters aren't so healthy for them. Crowder presented evidence at the annual meeting of the American Association for the Advancement of Science (AAAS) that colder or warmer waters can hinder shrimps' ability to accumulate certain lipids, a kind of fat that gives them enough energy to go through a molting cycle where they shed their shell, or exoskeleton, and grow to a larger size.
"The only way you get jumbo shrimp is for them to go through these molting cycles where they can get bigger and bigger," explains Crowder. "And the problem is that because of the physiological stress that they face due to the low oxygen zone and the displacement to cooler and warmer temperatures, they accumulate less lipid. And so we have new evidence from sampling shrimp from around the edge of the dead zone, further from the edge of the dead zone, and in the same sort of depths and temperatures in areas west of the dead zone, there's a significant impact on the lipid levels that occur in these shrimp."
image: Florida Dept. of Agriculture
And it's a problem that goes beyond your dinner plate, according to Don Scavia, environmental scientist at the University of Michigan. "Of course if it's just having a bit smaller shrimp, that's not a particularly huge problem. The problem is that if the shrimp are growing slower, and the population size is growing slower, and we continue to fish at the rates that we've traditionally been fishing at, we may fish faster than they can actually grow," he says. "The worst-case scenario is if this dead zone is maintained into the future or even worse, grew, that the fisheries could in fact collapse. This has happened in other parts of the world."
Scavia led a task force that in 2001 recommended decreasing nitrogen runoff by 30 percent in order to shrink the dead zone from around 6,000 to 2,000 square miles by 2015. But based on new computer models, Scavia published a more recent paper that predicts nitrogen runoff will need to decrease by 40 to 45 percent.
So far progress has been slow, but Scavia is confident the dead zone can be cleaned up. "If you think about fishermen and farmers, they have a lot in common," he says. "They're both trying to make a living off the environment. I think both groups understand each other's issues and each other's problems. I've never really seen these two communities at odds with each other; I think they understand each other. I think the battle lines were drawn, or most of the controversy was between the environmental groups and the fertilizer industry. And I think once we get to the farmers and the fisherman, I think we'll get more solutions."
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