Better Crawfish Aquaculture Through Research

Linda Benedict, Romaire, Robert P., Mcclain, William R.  |  5/22/2009 9:21:49 PM

W. Ray McClain and Robert P. Romaire

The domestic crawfish industry is the only large-scale, commercially viable crustacean aquaculture industry in North America. With more than 110,000 acres of crawfish ponds, Louisiana’s 1,600 farmers produce 35 million to 50 million pounds annually worth $25 million to $35 million at the producer level. Another 800 commercial fishers harvest crawfish from natural wetlands, primarily the Atchafalaya River Basin, the largest overflow swamp in the United States.

Annual harvest from the Basin varies with water discharge that depends on precipitation patterns in the middle and upper Mississippi River Valley. Harvest may be 60 million pounds in high water years and almost nothing in low water years. These unpredictable harvests, combined with increased consumer demand, provided much of the impetus for the development of crawfish aquaculture. The beginning of crawfish aquaculture in Louisiana was somewhat humble with only about 40 acres in 1949, but the industry has grown from an incidental crop to a vital agronomic venture.

Crawfish aquaculture is managed either as a sole crop or as part of integrated farming enterprises in which rice is the principal crop. To use natural and economic resources efficiently, many rice producers double-crop crawfish in rice fields after the rice harvest. More than half the crawfish in Louisiana are now cultured in rice fields (Figure 1).

Crawfish evolved in seasonally flooded wetlands, and current pond production is based on the annual wet/ dry cycles to which the crawfish have become adapted. Unlike the culture of many aquatic species that require hatcheries and formulated feeds, crawfish culture is based on selfsustaining populations that use a foragebased food web for acquiring nutrition. Crawfish retreat to burrows to survive the summer dry period and to reproduce (Figure 2). Growth of the offspring occurs in the shallow, forage-laden ponds during the fall, winter and spring, and market size animals are harvested with baited traps from about December through May.

Before 1987, there was no established pricing system based on graded and sized crawfish. Pricing was influenced largely by supply and demand with little regard to size, above a minimum acceptable level. The principal emphasis of management for the crawfish producer was to maximize total production of harvestable crawfish.

In 1987, a major export initiative of crawfish to Sweden prompted the crawfish industry to establish grading practices, which subsequently influenced the production and marketing of crawfish and influenced crawfish research efforts. The export market was lucrative and demanded only select crawfish of the largest size. To effectively segregate crawfish for this market, the industry devised grading processes. The establishment of grading in the industry allowed not only the segregation of crawfish for export but also for domestic markets. Grading by size became a standard industry practice. Crawfish are routinely graded into three size grades: large for the high-value export market, medium for the domestic live or restaurant markets and small for the processed tail meat market.

Historically, the most significant problems facing Louisiana crawfish producers have been low yields, harvest of small, sub-marketable crawfish, or low profitability resulting from inefficient harvesting techniques. Low yields result from reproductive failures and deaths, usually juvenile crawfish. Production of small or stunted crawfish occurs mainly from overpopulation, often exacerbated by food shortages and sometimes poor water quality. Inefficient harvesting occurs when trapping intensity is insufficient or too great, or when the most efficient traps or baits are not used.

Since 1966, Louisiana Agricultural Experiment Station (LAES) researchers have been addressing the needs of Louisiana crawfish farmers. They have a strong track record of developing new technologies that have been adopted by the industry. Ag Center research has led to a better understanding of the factors that affect crawfish production, including identifying poor water quality (low dissolved oxygen) as the primary cause for massive mortalities of newly hatched crawfish. Water management strategies (such as delayed flooding and water circulation and flushing) were developed and are used by producers to manage for better water quality. Research determined that planted forage crops were the most effective for establishing a sustaining food system and found rice to be the most dependable forage.

Today, most crawfish farmers plant rice as the forage crop. Supplemental feeding of agricultural byproducts and formulated feeds was investigated and, although found to be somewhat effective, it was usually not economical. Harvesting research determined the optimum density of traps, optimal bait soak time and, probably most significant, led to the development of formulated (pelleted) baits that replaced much of the fresh-frozen fish baits. Today, feed manufacturers sell $4 million to $5 million of formulated crawfish bait each year, nearly half of the total crawfish bait market.

Research during the 1990s has continued to address production needs of the crawfish industry, with special focus on producing larger crawfish. Small crawfish are least valuable, but the highest percentage of the cultivated crawfish crop traditionally falls into the smallest category.

Compounding the problem of smallcrawfish, beginning in 1991, Louisiana’s crawfish industry was hurt by massive imports of crawfish tail meat from China at below fair market value. In 1996, 8.5 million pounds of imported crawfish tail meat (nearly 56 million pounds of live weight equivalent) displaced more than 90 percent of Louisiana’s domestic crawfish meat market. Crawfish producers lost markets for small crawfish that were traditionally peeled and were subsequently deprived of a significant source of income. Although a tariff was imposed on most of the importers in 1997 and eased the situation, research emphasis has been directed at production of larger crawfish and improving production efficiency.

LAES researchers determined that overpopulation is the single most important factor affecting crawfish size at harvest. Renewed scientific investigations into supplemental feeding in the 1990s showed that harvest size and yields could be marginally increased by feeding, but feeding negatively affected catch by interfering with the effectiveness of the baited trap, and feeding alone could not negate the effect of overcrowding. Researchers learned that overcrowding was caused by many factors, including a high levee area to pond surface ratio that increases the burrowing area for crawfish. It was determined also that extensive levee renovation hurt crawfish production by destroying adult and newly hatched crawfish in the burrow. Producers, dependent on natural recruitment from broodstock contained in the pond, have little control over populations but now have a better understanding of crawfish population dynamics and that relationship to production. Means to control overpopulation and to augment low populations have been the focus of recent research efforts by LAES scientists; although promising results have been attained, few recommendations have yet been developed.

Harvesting costs account for 50 percent to 70 percent of the cost of producing farm-raised crawfish, and findings from harvest research conducted by LAES scientists have translated into significant savings in bait and labor costs. Reductions in harvesting days and bait use with the more efficient pyramid trap (Figure 3) was achieved without reducing yield, but with significant savings in harvesting cost. Additionally, it was shown that with reductions in trapping intensity, larger crawfish could be harvested. Industry adoption of these harvesting practices is estimated to have saved the industry $2 million to $3 million annually since 1993. More recently, research has determined that trap harvesting becomes more efficient when bait type is alternated daily. This is a “no cost” management tool thought to work by maintaining a more distinct scent gradient, thus increasing the attractiveness of the bait.

The LSU Ag Center is committed to working on behalf of the Louisiana crawfish industry and will continue to address production concerns of the crawfish producers through applied research. Financial support of crawfish research has been provided from several sources including the Louisiana Crawfish Promotion and Research Board (through check-off funds), USDA Special Grants Program, the Louisiana Board of Regents LEQSF program and the USDA’s Southern Regional Aquaculture Center.

W. Ray McClain, Professor, Rice Research Station, LSU Agricultural Center, Crowley, La.; Robert P. Romaire, Resident Director and Professor, Aquaculture Research Station, LSU Agricultural Center, Baton Rouge, La.

(This article was published in the fall 1999 issue of Louisiana Agriculture.)

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