Crawfish Connection - November 1 2007

Richard Johnson, Shirley, Mark G., Romaire, Robert P., Lutz, C. Greg  |  10/30/2007 6:42:25 PM

Managing Water Quality Following Fall Flood-Up

As we enter the month of November a majority of producers have completed flooding of their ponds or are in the process of completing filling of ponds. With flooding comes not only opportunity for a promising crawfish season but also potential problems that the producer must be aware of and manage for. Fall flooding from mid-September through early November coincides with peak spawning (reproduction) of females. Early flooding of ponds may not offer significant advantages of early-season harvest for the producer if a majority of females have not yet laid and hatched eggs. By late October, a majority of females have laid eggs and young hatchlings are ready to emerge. Rainfall in October and November assists in the emergence of females from the burrows, particularly those located high on the levees.

The largest concern at this time of the year in crawfish pond management is maintenance of water quality that will insure good survival of the young and fast growth. Good water quality in the fall is synonymous with having an adequate concentration of oxygen dissolved in the water. Although crawfish have the ability to survive exposure to relatively low oxygen levels for short periods, research has shown significant mortality or slow growth of young can occur when oxygen levels remain below 1 part per million (ppm) for an extended period of time. Measure oxygen with a chemical test kit or an oxygen meter.

The most important factor that influences oxygen levels in ponds is water temperature. Although warm water is advantageous to the growth of crawfish, at the same time, the warmer the water is in a newly flooded field, the more rapidly oxygen will be consumed and depleted in the breakdown or decomposition of vegetative forage that was established during the summer as a food resource for crawfish. Just about all ponds will have some degree of problem associated with low oxygen in the first month or two following fall flood-up. The severity and length of the problem will depend on several factors, including water temperature, the type and quantity of vegetation in the pond at flood-up and the depth to which the pond is flooded in early fall.

Usually, oxygen problems develop about two weeks after ponds are flooded and continue until such time that water temperature cools to around 60 degrees, usually sometime from mid-November into December. The warmer the temperature, the higher the rate of vegetative decomposition and the more severe will be the problem with low oxygen. Oxygen is consumed in the decomposition of vegetation. Also, warmer water cannot hold as much oxygen as colder water.

Of course, the producer has no ability to control and manage water temperature, but several steps can be taken to minimize the impact of low oxygen concentration on crawfish health. Usually oxygen problems are less severe in monocropping ponds in which rice is planted as forage in August and is still green at flood-up. Ponds in rice-crawfish rotations with significant amounts of rice straw spread throughout the field following grain harvest can usually be expected to have more severe oxygen problems extending over a longer period of time. Ponds with non-planted volunteer forage, particularly terrestrial grasses, will usually have more severe water quality problems than ponds with rice or other planted forages. Ponds with sorghum-sudangrass as forage appear to have somewhat more severe oxygen problems than ponds with rice, but it is manageable if ponds are not flooded too early or too deep in the fall.

Ponds need not be flooded to full depth during the 1- to 2-month period in the fall when brood crawfish and their young emerge from their burrows. Shallow flooding in the early fall reduces the amount of vegetation that is underwater and subject to decomposition. This can reduce the severity of low oxygen. It is also cheaper to replace four to six inches of water in a pond that is deficient in oxygen than 12 to 18 inches if flushing the pond is warranted. Young crawfish can successfully grow in as little as four to six inches of water, especially if abundant vegetation provides cover. During the period following initial flooding, maintaining high oxygen levels is more important than filling the pond to its full depth. The pond should be filled to maximum depth when oxygen problems subside in early winter.

If you have low oxygen, what can you do? We used to routinely recommend “pumping and flushing” ponds to improve oxygen levels, but given the high cost of fuel and size of many ponds, this might not be the most effective management plan. Managing low dissolved oxygen by flushing out low-oxygen water and pumping in good, oxygenated water can be a hit-or-miss proposition for many producers. First, many farmers do not have sufficient pumping capacity to effectively flush ponds to maintain adequate concentrations of oxygen. If you are not capable of filling your pond(s) in four to five days after the ground is wet, you likely do not have sufficient capacity to effectively manage oxygen by flushing. Pumping and flushing if you do not have sufficient pumping capacity is expensive and not likely to improve production. If you do have adequate pumping capacity to completely exchange water in your pond(s) in four to five days, measure your oxygen and consider flushing when oxygen levels drop below two ppm.

When flushing a pond to replace low oxygen water, it is better to drain some of the low-oxygen water from the pond, usually by dropping the water level by ½ to ?, and then refilling the pond to the previous level. This is more effective than pumping and draining at the same time. Of course, be sure you have an effective aeration screen to aerate incoming water whether pumping from a well or surface waters.


What About Supplemental Feeds?

Although we hope you were able to establish a good forage crop this past summer to carry you through the production season, it is not uncommon for a variety of reasons for some producers to have a lack of adequate forage. We are frequently asked what can be done to supplement the food supply or if adding supplemental feeds or hay to a pond is an effective management tool. Considerable research has been conducted for nearly 30 years on this topic, which has involved evaluating dozens of potential supplemental crawfish feeds ranging from low-cost agricultural by-products and hay to higher-cost formulated feed pellets developed for fish and shrimp. The bottom line of all these studies is that little or no noticeable cost-effective benefit is predictably derived from supplemental feeding of crawfish in commercial ponds. Thus, we do not currently recommend supplemental feeding as a practical management tool in crawfish farming. Practical logistical issues of handling feed, distribution of feed supplements throughout the pond and frequency of feeding are larger issues associated with supplemental feeding in crawfish ponds than nutritional considerations of the crawfish themselves. We will speak more on this topic in future newsletters.


Preparations For Crawfish Harvest

Before you know it, we will be just around the corner starting crawfish harvest. As most of you know, labor and bait associated with harvesting are among your highest expenses in farming crawfish. It pays to be as efficient as possible. Your goal should be to use the least amount of labor and bait to remove your crawfish crop from ponds over the next five to six months. Now is a good time to review basic trapping guidelines in preparation for the upcoming harvest season. If you have not already done so, first you will need to establish harvesting rows (lanes) for your traps. The following table will provide you with information on how wide your trapping rows should be spaced and the distance between your traps to obtain your desired number of traps per acre. For example, if you are targeting fishing 18 traps per acre in your pond, your distance between trapping lanes or rows should be about 40 feet and distance between traps in the row should be about 60 feet. Or you could place your rows at 60-foot intervals and space your traps at 40-foot intervals.

Trap Density and Spacing

Distance Between Rows     Distance Between Traps     Traps/ Acre

                40                                             30                             36

                40                                             40                             27

                40                                             50                             22

                40                                             60                             18

                50                                             40                             22

                50                                             50                             17

                50                                             60                             15

                60                                             30                             24

                60                                             40                             18

                60                                             50                             15

                60                                             60                             12

                70                                             30                             21

                70                                             40                             16

                70                                             50                             12

                70                                             60                             10

Pyramid traps made from ¾-inch square welded wire will catch on average about ? more crawfish by weight than ¾-inch hex-mesh traps or traps made from ?-inch square wire because they retain smaller crawfish. But this can differ from pond to pond depending on crawfish density and crawfish size. In low-density ponds with exceptionally large crawfish, you may not see much difference in size or catch between traps made with different types of wire or mesh size.

Evenly distribute traps at a rate of 18-22 traps per acre for high-crawfish-density ponds. High-crawfish-density ponds are usually those in which the pond is managed solely for crawfish (crawfish monocropping) and crawfish are produced in the same pond year after year.

Distribute 10-15 traps/acre for low-crawfish-density ponds. Low-density-crawfish ponds are usually those in which crawfish are not grown in the same field year after year, such as is practiced in rice-crawfish field rotational systems.

We will discuss baits, baiting recommendations and frequency of trapping in the December newsletter.


Production Manual And Other AgCenter Resource Information

If you do not yet have a copy of the updated “Louisiana Crawfish Production Manual,” contact your county agent to receive one. Other publications on crawfish can be found on the LSU AgCenter Crawfish website.


Meeting Announcement

The Louisiana Crawfish Farmers Association will also host the Crawfish '07 Expo for members and vendors at the Rayne Civic Center, Rayne, November 6, 2007. Time of the trade show is 8:00 a.m. – 3:00 p.m. A crawfish educational program will be held in conjunction with the trade show. For further information, call the association office at (337) 394-8182.

If you have any questions about your particular situation, contact one of the crawfish specialists with the LSU AgCenter for assistance.

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