Asian Shrimp Disrupt Delicate Balance
First it was the catastrophic BP spill, then it was the chemical dispersants used to shoo the errant petroleum to less incriminating locations like Minnesota, now it’s Asian tiger shrimp (Penaeus Monodon) that are threatening disrupt the delicate balance of the waters of the Gulf of Mexico. Sightings of the giant cannibal shrimp – which can grow to over one foot long and one pound in weight – have increased ten times over from the Carolinas to Texas in 2011 and twenty fold in the beleaguered Gulf waters off Louisiana. In fact, there were so many reports about the creatures showing up in the catches of the state’s commercial and recreational shrimp fishermen last year that Louisiana Wildlife and Fisheries officials couldn’t keep up with them.
The shrimp, which have black and white stripes across their backs and tails similar to their jungle cat namesakes, are aggressive and consume more resources than native Gulf shrimp, prompting concerns they will eventually out-eat and out-grow their smaller rivals. And they multiply prolifically. Tiger shrimp can produce about 1.5 million eggs a spawning season versus the approximately 500,000 typical of their Gulf shrimp cousins.
Carnivores and Cannibals
The Asian tiger shrimp is also carnivorous and, like other adult shrimp, are not above eating their own when they get the munchies. An early study reported that about 85 percent of a wild tiger shrimp’s diet consists of crustaceans, composed of small crabs, mollusks and smaller, native Gulf shrimp, topped off with a soupcon of budding Gulf oysters. That puts the marine invader in direct competition with the Gulf seafood industry for the fruits du mer that have supported it for centuries.
Because the Asian shrimp is capable of altering fragile marine ecosystems simply by virtue of habitation, scientists from the National Oceanic and Atmospheric Administration (NOAA) are launching a research program to evaluate its biology and ecology. As with all non-native species, there is the prospect of deadly new diseases and parasitic transmission. Viruses in particular can quickly wipe out shrimp populations, and the tiger shrimp have a documented history of spreading them. There is also the inevitable war of survival between the foreign and native shrimp stocks, especially given the size and high spawning rates of the Asian tiger shrimp as compared with other species.
How Did an Alien Crustacean Species From Indo-Pacific, Asian and Australian Waters Reach the U.S.?
The truth is that little is known about wild tiger shrimp – let alone about their migrating habits. Up until now most scientific studies have focused instead on their smaller farmed relative, motivated no doubt by economic incentives and the relative ease with which they can be observed and tested in controlled conditions. However, theories about the invasion of the giant shrimp are beginning to take shape.
Native to Asia, where they are most common, biologists believe the tiger shrimp have also established populations off the coasts of West Africa, South America and the Dominican Republic owing in large part to periodic escapes from fish farms. And in fact the first time that the species attracted the attention of US marine scientists was in 1988 when 2000 shrimp were accidentally released from a commercial fish farm in South Carolina. By 2006 their territory had expanded throughout the waters off Louisiana, Florida, the Carolinas, Georgia, Mississippi and Texas.
It has been theorized that the tiger shrimp currently turning up in the Gulf might have surfed Caribbean Sea currents following a 2005 hurricane hit to a shrimp farm in the Dominican Republic. It is also possible that they were transported in ballast water from ships. Or it could be a simple matter of the original South Carolina escapees breeding like crazy.
Privatizing the Invasion: Why Not Let the Free Market Solve the Problem?
Tiger shrimp are edible with a taste described as similar to that of lobster – which conjures up a vision of a lucrative market for the massive shellfish. After all, their smaller relatives are one of the most-farmed shrimp species in the world. But will their rise in popularity occur to the detriment of the US’s native shrimp population?
For now, the numbers of giant Asian tiger shrimp in US waters are dwarfed by those of our own native shrimp.
The giant Tiger shrimp has yet to establish a tipping point in the Gulf, which in this case would be indicated by a breeding threshold large enough to establish a self-sustaining population. Still, there is nothing to inhibit their spread with the exception of the Gulf’s winter water temperatures – which are colder than the tropical temperatures in which they ordinarily reproduce and grow. When scientists examine the DNA of the Asian natives and their wayfaring relatives, they may not only find valuable clues to the émigrés’ origins – but as to whether they are on a evolutionary crash course that will allow them to adapt to their adopted home.