Article for September - October 2008
For Wildlife Watchers: Shrimp
by Rob Simbeck
photography by Phillip Jones
Shrimp are prolific breeders, and given the dramatic decline in the number of shrimpers, their population can be expected to continue to do well, barring adverse environmental conditions.
In the natural world, the wondrous isn’t hard to come by. Owls fly noiselessly. Flies can land upside down. Many snakes can unhinge their jaws. Look deeper and tinker a little, and things get even better. An enzyme in the stomachs of calves makes cheese possible. Compounds taken from fireflies were used to test for life on Mars.
White shrimp - Litopeneaus setiferus
Brown shrimp - Farfantepanaeus aztecus
Pink shrimp - Farfantepanaeus duorarum
Description: Shrimp range from a fraction of an inch to 9 inches long, with exoskeletons in three parts, antennae and fourteen pairs of appendages.
Range and Habitat: Species inhabit many of the world’s ocean waters. They can be found along most of the South Carolina coast, with good concentrations in some pockets.
Reproduction: Prolific breeders, spawning in the spring (white and pink shrimp) and late fall (brown shrimp).
Viewing Tips: Estuaries and near-shore waters. Often caught as bait and observed jumping in boat wakes in shallow waters.
And then there is chitosan. This remarkable compound is derived from a natural substance that is tossed into trash bags and washed down garbage disposals by the ton—in the shells of shrimp and some other crustaceans. It’s “bioadhesive,” so it sticks to damp human tissue and helps clot blood. It also has natural anti-bacterial properties. It’s perfect for bandages, and it’s used for that purpose in Iraq. In other settings, it enhances plant growth, helps defend against fungal infections and can help purify water, wine and beer.
Outside the human purview, chitosan, a form of chitin, plays a key role in molting, something shrimp do pretty regularly. Chitin takes the stage after a shrimp sheds its exoskeleton, becoming a framework for the fusion of calcium carbonate. Calcium carbonate is omnipresent in seawater and is responsible for forming the shrimp’s new, larger exoskeleton.
A shrimp’s life cycle involves well over a dozen molts. It begins as females lay half a million to 1 million eggs each from near the beach to a few miles offshore. Within a day, each egg, just one sixty-fourth of an inch across, has hatched and the larval shrimp, or nauplius, feeds on yolk reserves. The nauplius is essentially just another speck of plankton at this point, and the growing shrimp remains in this form for four more stages.
The shrimp undergoes three stages as a protozoan, in which it develops mouth parts and an abdomen, begins feeding on algae and reaches about a twelfth of an inch in length. Three mysid stages grow the shrimp to a fifth of an inch in length and give it the beginnings of legs and antennae, and two post-larval stages take it to about a quarter of an inch and give it the general appearance of an adult. Development is a rapid process that takes less than two weeks and moves the shrimp from the sea bottom to the brackish water at stream and river mouths.
As adults, shrimp grow rapidly, molting in a rhythm tied to lunar cycles since losing its shell leaves a shrimp extremely vulnerable and is best done in the darkness of the new moon.
The shrimp’s body is divided into three segments—head, thorax and abdomen. The head and thorax are fused together and covered by a carapace that encloses the gills and comes to a point called the rostrum. The head has eyes on stalks and at least two pairs of long antennae. There are fourteen pairs of appendages—the first three, near the head, are modified into mouth parts called maxillipeds; the next five are walking legs attached to the thorax; there are five pairs of swimming legs on the abdomen and one pair forming part of the fan-like tail. The ten pairs of walking and swimming legs justify the name decapod, which includes crabs and lobsters.
Most human appreciation of the shrimp is, of course, culinary. We’re drawn to the shrimp’s muscular body, which, boiled or pan fried with butter and garlic, provides one of the most exquisite human dining experiences. Three species found in South Carolina waters—there are 2,000 species worldwide—are regularly used as human food. White and brown shrimp are common, and pink shrimp are rare.
The commercial shrimping industry, which services the human hunger for shrimp, has fallen on extremely hard times recently.
“There are multiple factors,” says Amber Von Harten, a fisheries specialist who works with the state’s Sea Grant Extension Program, “the first being the flood of imports of pond-raised shrimp hitting U.S. markets, driving prices down to what shrimpers were getting in the 1960s.”
“Working inflation and fuel prices into the computation,” adds David Whitaker, assistant deputy director of the SCDNR’s Marine Resources Division, “would show an even worse scenario for fishermen. Taken together, these factors have resulted in significant changes in fishing behavior—shrimpers fishing only when catches are expected to be good.”
The shrimp catch has fallen from a peak of 6.9 million heads-off pounds, valued at $21.6 million in 1995, to just 1.7 million pounds valued at $5.4 million in 2007. The number of commercial licenses purchased has dropped from 1,502 in 1981 to just 378 in 2007-08.
For more on the South Carolina shrimping industry, see “Living for Shrimping, Shrimping for a Living,” in the May-June 2007 issue of S.C. Wildlife magazine. Read this article on the Web at http://www.scwildlife.com/pubs/mayjune2007/shrimping.html.
Small white shrimp overwinter in estuaries and become the next spring’s spawning stock, although their numbers can fall greatly if the water temperature reaches 46 degrees or below. For brown and pink shrimp, reproduction begins when the male shrimp transfers a sperm packet to the molted, softshelled female, who stores it until she is ready to spawn. White shrimp mate in between molts when the shell is still hard, with the male attaching a sperm packet to the female’s underside.
Shrimp are prolific breeders, and given the dramatic decline in the number of shrimpers, their population can be expected to continue to do well, barring adverse environmental conditions. Worldwide, a dramatic increase in shrimping, most in the form of shrimp farming, has had dramatic environmental and economic effects. Still, this widely exploited species remains one of the world’s most important seafood products, even if its future as a commercial product in South Carolina remains problematic.
Rob Simbeck is an award-winning free-lance writer living in Nashville, Tennessee.
© 2008 South Carolina Wildlife Magazine, September - October 2008 - www.scwildlife.com