© Houston ChronicleA tiger prawn is displayed by shrimp trawler Capt. Tony Perez. The foot-long female was caught about 60 miles south of the Louisiana coast near Morgan City in October.
The Asian tiger prawn, a foot-long crustacean with a voracious appetite and a proclivity for disease, has invaded the northern Gulf, threatening prized native species, from crabs and oysters to smaller brown and white shrimp.
Though no one is sure what the ecological impact will be, scientists fear a tiger prawn takeover could knock nature's balance out of whack and turn a healthy, diverse marine habitat into one dominated by a single invasive species.
"It has the potential to be real ugly," said Leslie Hartman, Matagorda Bay ecoystem leader for the Texas Parks and Wildlife Department. "But we just do not know."
The tiger prawns from the western Pacific - which can grow up to 13 inches long - have been spreading along the Gulf Coast since 2006, but their numbers took off this year. Shrimpers pulled one from Texas waters for the first time in June.
In all, shrimpers have found three tiger prawns in Aransas Bay, one in Sabine Lake near the Louisiana border and one in Gulf waters about 70 miles from Freeport, according to the Texas Sea Grant program at Texas A&M University.
Marine scientists will conduct genetic studies on the shrimp to determine their origin. Hartman said they will need at least 60 prawns for an accurate analysis.
Several theories
Some speculate that the Gulf invasion began with an accidental release of farmed prawns in South Carolina in 1988. Another theory: The prawns may have escaped from flooded industrial shrimp ponds in the Caribbean Sea during recent hurricanes.
The threat underscores concerns about large-scale fish farming, also known as aquaculture, in the Gulf. The federal government opened the waters to fish farms in 2009 despite fears from environmental and fishing interests over how to protect wild stocks.
Disease normally would exist in relatively low levels in fish around the Gulf but can run rampant in densely packed fish farms. Tiger prawns are a known carrier of at least 16 viruses, such as white spot, which can be lethal to shrimp.
The Gulf policy calls for only native species to be farmed, but it does not have the force of law, said George Leonard, who leads the Ocean Conservancy's aquaculture program.
"We need to be really, really cautious," Leonard said. "There has to be rules and regulations."
No farming of species
Texas allows industrial-scale shrimp ponds, but requires permits for the cultivation of non-native species. No one in the state is farming tiger prawns, said Tony Reisinger, a marine and coastal resources expert for the Texas Sea Grant program.
Marine scientists have yet to find any juvenile tiger prawns in Texas waters, a sign that the species is breeding. It is a difficult assignment because they look similar to native white shrimp at a young age.
Tiger prawns weigh more than a half-pound and have distinctive black and white stripes on the tail. They eat the same types of food as native shrimp species, but also prey on their smaller cousins, as well as crabs and young oysters.
"It's a large, competitive species," Reisinger said.
It's also tasty, fetching a higher market price than native brown shrimp on the New York market this month.
Some shrimpers have wondered if the large prawns could become the fourth harvestable shrimp species off the Texas coast.
Hartman, of Texas Parks and Wildlife, is skeptical.
"It could be another crop, but at the expense of our native crop," she said.
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