American Scientist

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.

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.

Farming Crustaceans

Adult crawfish stocked into new ponds in the spring burrow into the enclosing mud levees before the shallow pools are drained for the summer. There is no real control of how many crawfish survive, so there is no way to regulate the number of young crawfish that appear when these impoundments are refilled in the autumn. Because the growth of the animals slows when their density is too high, a given pond may have so many crawfish that they do not reach sizes that are desirable to market. In such cases, allowing birds to reduce the density of crawfish seems a logical method to assure adequate growth.

Thus many environmentalists contend that crawfish farmers should be happy that water birds thin their crawfish crops. The rub is that when small crawfish are culled in experimental ponds, there is no substantial compensatory growth in those remaining. Only when these same small crawfish are moved to underpopulated ponds do they thrive and attain large size. It would appear that some unidentified environmental factor in the original pond must limit the ability of small crawfish to grow there. In any event, computer simulations support the position of the farmers: Heavy predation from birds, regardless of the species involved, probably hurts crawfish production.

Louisiana crawfish aquaculture is also threatened by another increasingly common phenomenon: globalization. The problem is that the importation of frozen crawfish products from China has depressed market prices. Many crawfish farmers, disappointed by the loss of income, are instead trying to raise other crops, such as sugar cane, that do not require them to flood the land. As a way to make ends meet, some have begun leasing the right to hunt the many ducks and geese that visit their ponds.

If Louisiana crawfish aquaculture disappears, it is not only the farmers that will be displaced. Consider one well-known rookery for wading birds at Lake Martin, just east of Lafayette. This vast breeding ground—a breathtaking site to visit—undoubtedly takes this spectacular form because it is situated within 25 miles of some 30,000 acres of crawfish ponds, which support, in large part, these nesting birds and their offspring throughout most of the year. Losing too much crawfish acreage in that vicinity would thus devastate the rookery, which would be an environmental tragedy.

End of an Era?

Thanks to the rise of crawfish aquaculture, Louisiana provides the wintering and spring nesting grounds for a major portion of the wading birds inhabiting North America. What is more, the marginal areas around crawfish ponds shelter countless owls, hawks, eagles and ospreys, as well as migrating shorebirds and neotropical songbirds, not to mention their more sedentary cousins. The agricultural community in this one state has thus helped to maintain the legacy of an entire continent's birds—while doing quite well for itself—over the past half-century.

But crawfish farmers now need incentives to continue their traditional practices. A healthy crawfish industry is certainly important to the economy of Louisiana—and so is a healthy suite of wetland birds. Such flocks improve the quality of life for all residents and, in places like Lake Martin, can increase opportunities for eco-tourism, an avenue to greater income that crawfish farmers need to pursue more vigorously. Private and government conservation agencies can also help by subsidizing the construction and maintenance of crawfish ponds, just as they now pay for the creation of other sorts of artificial wetlands. Scientists, too, might be able to bring crawfish farmers and environmentalists closer together, if we can figure out how predatory birds can serve to thin overpopulated crawfish ponds in a way that boosts the size of those remaining. It is my hope that such efforts will effect meaningful changes soon, so that two treasured natural resources—crawfish and water birds—can be sustained on into the 21st century.