Charles Lutz, Romaire, Robert P. | 3/31/2005 1:08:26 AM
Robert P. Romaire
Over the past decade, researchers at the LSU AgCenter’s Aquaculture Research Station have investigated crawfish harvesting methods to reduce production costs and increase management efficiency. Crawfish are harvested differently from other types of cultivated fish such as channel catfish. These other fish are harvested once or several times a year with nets and seines. However, the presence of cultivated crops such as rice or volunteer vegetation, grown as food for crawfish in ponds, interferes with seines and requires that crawfish be harvested with small, baited traps over an extended period, beginning as early as mid-November and continuing through April or June.
The seasonal catch in crawfish in ponds is highly dynamic, often varying as much as 200 percent daily (Figure 1). It is influenced by many factors including water temperature, water quality, type and quantity of vegetative forage, weather, lunar phase, as well as crawfish reproduction, growth and molting patterns. Generally, two-thirds of the crop is harvested from March through May, when densities of marketable crawfish are highest. Trapping is labor intensive, and nearly two-thirds of total production costs in crawfish farming operations are associated with harvest. Bait and labor are the major costs. Clearly, modest increases in trapping efficiency can significantly reduce production costs and increase profitability.
Research at the Aquaculture Research Station has focused on investigating trapping and baiting strategies for crawfish with the highest potential to reduce bait and labor costs. The studies were conducted in six large experimental ponds (4 to 5 acres each) managed for crawfish production according to commercially recommended practices.
In one study, two traps – a pyramid design with three entrances and a stand-up pillow trap with two entrances – were evaluated. Crawfish were trapped three days a week. Pyramid traps had a 44 percent higher catch than stand-up traps. An increase in trap density from 12 to 24 traps an acre increased yield 49 percent, but the increase to 36 traps an acre increased crawfish yield only 8 percent. The most efficient harvesting strategy was to use pyramid traps set at 24 an acre. Because crawfish yield was excellent (more than 1,000 pounds an acre) with only three trapping days a week, follow-up studies were conducted over three production seasons to study the effects of trapping frequency (trapping days a week) on crawfish catch. Although several trapping strategies were investigated, including biweekly trapping and rotational trapping schemes, emphasis focused on harvesting crawfish five consecutive days a week, which was the standard, or three days a week. Pyramid traps were used at 24 an acre. Although crawfish yield was 17 percent higher with five days a week trapping (Figure 2), the 40 percent reduction in bait and labor cost and the 20 percent increase in crawfish harvest size demonstrated that three days a week was the most economical harvesting strategy.
Bait, which is required to attract crawfish into traps, is the biggest expense in crawfish production, costing from $40 to $200 an acre. Two general types of bait are used, natural fish baits, such as gizzard shad and menhaden, and formulated baits manufactured by feed mills. Formulated crawfish baits were initially developed in the early 1980s by LSU AgCenter researchers. They consist mainly of cereal grains, grain byproducts, natural and synthetic attractants, and binders. Fish baits are about 20 percent to 25 percent more expensive than formulated baits and require freezers for storage and labor to cut the bait into trap portions. The amount of bait used varies widely but generally ranges from 0.25 to 0.75 pound per trap per day.
Gizzard shad and a commercially available formulated bait were evaluated in both cold (January to February) and warm (March to May) water over two trapping seasons. On average, shad caught 39 percent more crawfish than the formulated bait in cool and cold water (less than 68 degrees F). In contrast, the formulated bait was 41 percent more effective in warm water (more than 68 degrees F) (Figure 3). The two baits were equally effective at temperatures near 68 degrees F. In a follow- up study, two natural baits, gizzard shad and menhaden, were compared with two formulated baits in cold and warm water (Figure 4). Crawfish catch was 50 percent higher in cold water with menhaden or shad compared to the formulated baits, but manufactured baits were 18 percent more effective than the fish baits in warm water.
In a companion study to the type of bait experiments, gizzard shad and a formulated bait were each evaluated at four quantities – 0.25, 0.33, 0.5 and 0.75 pound per trap in both cold water and warm water. Although crawfish catch increased with an increase in bait quantity above 0.25 pound per trap at all temperatures, the increase did not compensate for the increase in bait cost. Highest profit (gross value of crawfish minus bait cost) was achieved with 0.33 pound of bait per trap for both gizzard shad and formulated bait in cold and warm water.
Results from these studies have led to new recommendations in harvesting strategies for crawfish farmers. Trap designs, bait types, and trapping and baiting strategies were identified that reduced harvest costs significantly without major changes in established production methods. Significant reductions in trapping days and associated harvesting costs can be attained with little or no reduction in yield by using pyramid traps. Many crawfish farmers once trapped five to six days a week (100 to 150 days a season) and used as much as 0.5 to 0.75 pound of bait per trap. Crawfish farmers can obtain a comparable yield, but with significantly reduced costs, by selecting the appropriate bait or bait combination based on water temperature, not exceeding 0.33 pound bait per trap, and reducing trapping effort to three or four days a week (60 to 90 days a season), if they use pyramid traps.
Adoption of these harvesting recommendations over the past several years has saved crawfish farmers $2 million to $3 million annually in lower bait and labor costs. Despite these improvements in crawfish harvesting, crawfish harvest practices are still relatively inefficient and labor intensive. Further advances in crawfish harvesting technology can increase crawfish production efficiency and decrease the cost in farming operations. Better trap designs that minimize crawfish escape, development of formulated baits with enhanced effectiveness in cold water, and improved harvesting machinery to access traps in ponds are needed. Crawfish researchers at the Aquaculture Research Station and the Rice Research Station maintain an active research program on harvesting with the goal of further reductions in the cost of producing crawfish and increased profitability for crawfish farmers.
(This article appeared in the winter 2001 issue of Louisiana Agriculture.)