A big increase in reports of Asian tiger shrimp along the U.S. Southeast coast and in the Gulf of Mexico has federal biologists worried the species is encroaching on native species' territory.
The shrimp are known to eat their smaller cousins, and sightings of the massive crustaceans have gone up tenfold in the last year, biologists say.
The black-and-white-striped shrimp can grow 13 inches long and weigh a quarter-pound, compared to eight inches and a bit over an ounce for domestic white, brown and pink shrimp.
Scientists fear the tigers will bring disease and competition for native shrimp. Both, however, can be eaten by humans.
‘They’re supposed to be very good,’ Pam Fuller, a biologist with the U.S. Geological Survey told CNN. ‘But they can get very large, sorta like lobsters.’
The last U.S. tiger shrimp farm closed in Florida in 2004, without ever raising a successful crop, according to a USGS fact sheet about the species.
Reports of tiger shrimp in U.S. waters rose from a few dozen a year - 21 in 2008, 47 in 2009 and 32 in 2010 - to 331 last year, from North Carolina to Texas.
'That's a big jump,' Ms Fuller told the Associated Press.
'I've had fishermen tell me they have quit bringing them in.
'They are seeing large numbers in their catch - multiples per night,' said Morris, who works at the National Oceanic and Atmospheric Administration's Centre for Coastal Fisheries and Habitat Research in Beaufort, North Carolina.
The increase 'is the first indication that we may be undergoing a true invasion of Asian tiger shrimp,' he said.
'Nobody knows what happened to their stock. But they have not been commonly caught in the area where that fish farm was,' she said.
She said hundreds were caught along South Carolina, Georgia and Florida after a storm hit a South Carolina shrimp farm in 1988, but none was reported in U.S. waters for the next 18 years. Six were reported in 2006, and four in 2007.
To find out whether last year's increase was a one-time spike or the vanguard of an invasion, the agencies are asking people to keep a wide eye for tiger shrimp, to report where and when they find them, and bring back frozen tiger shrimp to help learn where they're coming from.