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MACROSCOPE

Crawfish and Water Birds

Jay Huner

Just imagine the thrill of seeing several thousand white egrets, ibises and blue-hued herons, along with a hundred or more scarlet roseate spoonbills, exploding from the shallows of a southern Louisiana wetland. One does not have to be a birder to be amazed by the color and magnificence of these stately wading birds. Fortunately, such sights are now commonplace from mid-autumn into early summer in the Bayou State, a consequence of the expansion of rice farming and crawfish aquaculture there.

Figure 1. White-faced ibis fly over snowy egretsClick to Enlarge Image

Brought nearly to extinction by hunters roughly a century ago, egret, heron, ibis and spoonbill populations have rebounded dramatically in southern Louisiana in the past 50 years. In other areas, the status of wading birds is not so rosy, as coastal wetlands succumb to the tide of development sweeping the American Sunbelt. Florida, for example, has long been noted for its many wading birds, but the loss of appropriate habitat in that state has forced some populations of these birds into decline. A million acres of coastal wetland in Louisiana have also disappeared, but the half million inland acres that are now flooded regularly to raise rice or crawfish have helped to compensate for that damage to the environment. So Louisiana's success merits attention—and nurturing.

Although most people in my state admire such birds for their beauty and applaud their resurgence, crawfish "farmers" have become increasingly concerned about the damage that these animals do to their "crop" of small crustaceans. I began work in crawfish aquaculture when I was a graduate student at Louisiana State University in 1972, and even at that time owners were concerned about wading birds raiding the 40,000 or so acres of ponds they had by then built.

Today, Louisiana crawfish farmers have nearly three times that area in production. For the most part, they use these shallow ponds to raise red swamp crawfish (Procambarus clarkii), which look like tiny lobsters and are similarly tasty. Farm-raised and wild-caught animals now contribute equally to the 50,000 or so tons of live Louisiana crawfish sold each year, which accounts for nearly half of the global trade in this delicacy.

Despite the healthy growth of their industry, crawfish farmers continue to complain loudly about losses from wading birds. They also worry about the large flocks of crawfish-eating cormorants, gulls, terns and, in some cases, pelicans, which have become common visitors to crawfish ponds in the winter and spring. Even coots, normally herbivorous, have become abundant and are feeding on crawfish to some degree.

Crawfish ponds are clearly water-bird magnets. Carnivorous birds have learned to take advantage of the concentration of nutrient-rich prey—crawfish, insects, worms, small fishes and tadpoles—that these artificial wetlands harbor. And herbivorous birds feast on the abundance of seeds and aquatic plants available in the ponds, which typically range from 10 to 20 acres in size and are normally a foot or so deep.

Actually, the ponds are kept that full of water for only part of the year, typically from mid-fall through mid-spring, which simulates the natural hydrological cycle that local wetlands experience. Crawfish farmers often use the summer months to cultivate rice in their ponds by putting just a few inches of water in them. Raising this second crop adds to their profits and does not interfere with the production of crawfish, which normally begins again in October. (Incidentally, the combination of crawfish and rice makes an excellent gumbo dinner.)

Raising crawfish in this way is relatively inexpensive because, unlike farmed shrimp, these tiny crustaceans do not need to be fed fish or vegetable meal. Crawfish are omnivorous and can devour the sundry small animals that proliferate once the plants in the ponds begin to deteriorate. They also eat the decomposing vegetation itself, along with various seeds and stray rice grains, where rice was grown during the previous summer. So even the herbivorous birds that do not feed on crawfish directly compete with them for food. But gauging the damage that birds do to aquaculture operations has proved difficult, in part because crawfish management is an inexact science.




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