Crawfish Pond Management
The two most critical production problems facing the crawfish industry are complete crop failure and the overproduction of stunted, low value crawfish. Crop failure is the result of too few crawfish, often resulting from poor recruitment or low survival of juveniles.
Harvests of small, stunted crawfish are usually the result of too high a density of crawfish. Stunting refers to the situation where crawfish simply stop growing before they reach a minimum harvestable size or desirable market size. This minimum size is usually 22-23 crawfish per pound or between 3 to 3.5 inches.
The major factors affecting crawfish growth are harvesting strategy, certain water quality conditions, food availability and food quality, genetic influences, population density or combinations of these factors. Harvesting strategy, water quality and food sources are generally manageable.
Research indi-cates that genetics and breeding programs show little potential for improving harvest size. The most important factor in the production of large crawfish is density. High density (more than 15/square yard) of crawfish produces small crawfish, and low densities produce large crawfish if food and water quality are adequate. With the current state of technology, density control is difficult. An active research program is under way to provide solutions.
Methods to minimize stunting of crawfish in subsequent seasons are based on preventive measures taken during the current season. These include rotating production into different fields, delaying flooding in the fall and draining the pond quickly in mid-spring.
Rotating production into different fields or letting a permanent pond remain temporarily drained after several consecutive years can be effective, but loss of production in ponds for an entire season could lead to lost revenue that could outweigh the benefits of density control.
Delaying the permanent flood in the fall could reduce survival of juveniles in the burrow. Although this could delay the peak of production, it can sometimes be an effective control because it potentially reduces the total number of recruitment classes. If there is a long, cool spring or ponds become low in forage, many late crawfish may not have enough time to reach harvestable size before the ponds are drained.
Another method has been draining the ponds earlier than normal, before too many crawfish become sexually mature, and draining the ponds quickly, stranding numerous crawfish before they have the opportunity to burrow. This method is not always effective in older ponds with many established burrows. There can also be a loss in income when the harvest is stopped early to drain the ponds.
Management practices that would yield predictable results within the same production system are lacking. Current practices being evaluated by researchers include: mid-season temporary draining, maximizing the use of forages, modifying the harvesting schedule and relaying.
Reduction of crawfish densities at mid-season is effective in some cases. To maximize effectiveness, the reduction must occur after peak recruitment of juveniles but before ponds warm to near optimal temperatures in the spring. If reduction occurs before the numbers of juveniles peak, too many will survive and stunting will occur. Reductions too late in the spring will not allow the crawfish that survive to grow to harvestable size.
Modifying the typical harvesting routine also shows a potential for producing larger crawfish. Trapping five to six days a week can reduce the average harvest size of crawfish because animals are removed before they can grow to a more desirable market size. Harvesting three days a week increases overall catch size, but the total yield is usually lower. The effectiveness of this reduction strategy will depend on population density and size structure, food availability, time of year, trap density and marketing conditions.
Relaying or transferring crawfish from a poor environment to an improved environment is highly effective in increasing crawfish size. Since crawfish and rice seasons overlap, it is common to have newly established rice fields at a time when crawfish stunting normally occurs in forage-limited crawfish ponds. This provides the opportunity of using the vegetative growth phase of rice production as a valuable resource for obtaining additional growth. This method can be biologically effective, but it should be analyzed closely for economic efficiency.
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