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 Home>Crops & Livestock>Aquaculture>Crawfish>Newsletters>

Crawfish News November 2010 (Vol 3, No 7)

 
Crawfish Newsletter November 2010 (Vol 3, No 7)
Crawfish Newsletter November 2010 (Vol 3, No 7)


The 2010 Louisiana Crawfish Promotion and Research Board (LCPRB) Check-off Referendum will be held at all LSU AgCenter parish Extension Service offices on Nov. 10, 2010, to reauthorize assessments on artificial bait and crawfish sacks (bags). 

The referendum, authorized by Act 679 of 1983 and Acts 330 and 492 of 1985 of the Louisiana Legislature, was created to determine the sentiment of Louisiana crawfish producers as to whether they favor an assessment:
  • of one-quarter of one cent (1/4 cent) per pound on all artificial crawfish bait sold within Louisiana
  • on each sack used to package live crawfish in the amount of one cent for each sack holding less than 25 pounds of crawfish
  • of two cents for each sack holding 25 pounds or more.

By law, the funds generated from the check-off are spent to promote Louisiana crawfish, for research on crawfish production and to provide educational information about crawfish and its nutritional value. The LCPRB administers the funds, which usually range from $80,000 to $100,000 per year. Board members represent producers of farmed crawfish, wild crawfish fishermen, crawfish processors, crawfish bait suppliers, retail outlet and restaurant owners, the Louisiana Farm Bureau and landowners engaged in crawfish production.

Persons who purchase artificial crawfish bait or crawfish sacks may obtain a refund of the assessment by written request to the Louisiana Department of Agriculture and Forestry with copies of receipts or invoices showing the amount of artificial bait or bags purchased.

The LCPRB’s authority to collect fees on bait and sacks must be reauthorized every five years. For the past 25 years, the LSU AgCenter has helped the industry carry out these referenda by allowing producers to cast their ballots at LSU AgCenter parish extension offices. The AgCenter has agreed to assist the crawfish industry with this activity again, and with input from the LCPRB the Nov. 10, 2010 date has been designated for voting. Extension Service parish chairs from every parish office, or the staff members they designate, are authorized to assist by conducting all prescribed duties necessary during voting.

PRODUCERS, PLEASE NOTE! 

By law, in order to be eligible to vote at their local parish Extension Service office, crawfish producers must sign a “register of voting producers” and provide proof of purchase of a minimum of 100 pounds of bait or 100 crawfish sacks during the preceding 12 months. Crawfish producers can vote in the parish they live in OR the parish where they farm or fish, but they may only vote once. Contact Dr. Greg Lutz, Aquaculture Research Station, LSU AgCenter, at 225-765-2848 for more information.




In preparation for the upcoming harvest season you will need to establish harvesting rows (lanes) for your traps. The table below gives you the spacing, in feet, between rows and between traps to obtain the desired number of traps per acre. For example, for 15 traps per acre, distance between rows should be about 50 feet and distance between traps in the row should be about 60 feet. Or alternatively you could space your rows at 60-feet intervals and place your traps at 50-feet intervals.

High Crawfish Density Ponds

We recommend 18 to 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, often providing yields near or above 1,000 pounds per acre.

Low Density Crawfish Ponds

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

Trap Density and Spacing

Distance Between Rows (feet)

Distance Between Traps (feet)

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




Dipping Crawfish
Dipping Crawfish
A dip net is a useful tool to assist you in monitoring whether or not you have had successful crawfish reproduction in your ponds. At a crawfish production meeting last February we had a number of farmers who were concerned they were not seeing any evidence of crawfish in their ponds. None of them owned or used dip nets to sample their population of small crawfish. We were not able to tell them if the most likely cause was from reproductive failure of the brookstock during the summer (death or lack of reproduction in the burrows), or if they had successful  reproduction but then lost the crop of juveniles after flood-up from poor water quality. If dip net sampling information had been available to them and us, we could have more easily diagnosed the problem and provided them with recommendations to minimize occurrence of the problem in the future.

When using a dip net, about 10 to 20 dips or sweeps pulled quickly across the pond bottom on a regular basis is usually enough for a good, quick population assessment in most ponds. You’ll tend to find more crawfish in patches of vegetation along or near the levee. Do not dip in areas where the grass is so thick that you cannot effectively pull the net along the bottom. The net is selective for small crawfish which is good because we are looking for evidence of successful reproduction.

You will usually get your best assessment of the success of crawfish reproduction one to two months after your pond is flooded, or several weeks following a substantial rainfall, particularly if conditions were dry (little or no rainfall) following the flood-up. Remember, many females burrowed high on the levee do not emerge from their burrows with young until heavy rainfalls occur in late fall and early winter. Several weeks are required for the hatchlings to leave the female and distribute themselves throughout the pond. Do not be immediately concerned if you are not catching small crawfish shortly after flood-up because many females may not have emerged and the distribution of those juveniles that have emerged is patchy – they have not yet spread throughout the pond. Crawfish are more active at night, particularly when the water is clear. If you’re not catching young crawfish with your dip net during the day, try dip-netting your pond at dusk or after dark. Be sure to look carefully in the net. Very small crawfish can be easily overlooked – particularly when vegetation and other debris are present in the net. You will also usually find some insects in the dip net, some of which eat juvenile crawfish, and others that will later be eaten by the crawfish as a food source.

Sampling crawfish with your dip net once every three or four weeks following flood-up should be adequate. What you are looking for is at least some small crawfish in the net, but don’t expect to find crawfish in every sweep. If you find two to four different size groups of juveniles one to two months after flood-up, that usually is an ideal situation and indicates you’ve had staggered recruitment, which is the best condition to achieve a good crawfish crop. 

It is difficult to predict yield and harvest size from the number of crawfish caught in a dip net - it is a better tool to verify whether or not you had successful reproduction. That said, we have documented yields of 800-1,000 pounds of crawfish per acre in experimental ponds with December dip-net sweep counts averaging from ¼ to one crawfish/sweep. As in any business, it’s a good idea to write down your observations on dip-net sweeps, to include the average number of crawfish per sweep and the number of distinct size groups for each pond. Compare these observations to your yield at the end of the production season. Over time it may provide you some basis for predicting yield on your individual farming operation.

We suggest the Model 270-F-12 dip net sold by Ed Cummings Inc., 2305 Branch Road, Flint, MI 48506 (1-888-566-6387). This net stands up to vigorous use. It has a 42-inch wooden handle, a 10- by 12-inch frame and the net. The net which is 12-inches deep, is made from 1/16-inch netting, which will catch the smallest crawfish. A net with 1/8-inch or 3/16-inch netting is also acceptable. The dip nets cost about $26 each. Similar nets may be available elsewhere.




Question

I am using 3/4-inch hex mesh pyramid traps and your newsletters and production manual state that 3/4-inch square mesh welded wire traps catch even smaller crawfish. I need to catch slightly bigger crawfish because my customers say my crawfish are too small. Do you have a chart that shows the minimum size crawfish (length and number per pound) that will be caught with the different types of wire?

Answer

Commercial pyramid traps come in two mesh sizes – 3/4-inch and 7/8-inch square welded wire. Few trap makers, if any, still use 3/4-inch hex-mesh wire. The 7/8-inch square mesh traps will on average retain larger crawfish than 3/4-inch square mesh traps, but with not much difference in overall catch over a harvest season. The 3/4-hex mesh traps and the 7/8-inch square mesh trap retain about the same size of crawfish. 

But the problem with your crawfish being small will not necessarily be corrected by using a larger-mesh trap. Harvested crawfish can be small for two reasons:
  1. A recruitment class of juveniles has grown to a size that it will be retained by the trap. 3/4-inch square mesh can retain crawfish as small as 35 to 40 count per pound; 7/8-inch square mesh can retain crawfish as small as 30-35 count per pound – both small as far as buyers are concerned. If growing conditions are suitable and the crawfish are not yet mature, the average size of crawfish should increase with time.
  2. The second reason is because the crawfish population is overcrowded and food resources may be limited. Growth and size is mostly controlled by population density and the more crowded crawfish are the smaller they are going to be when caught. Overcrowding is more common in smaller ponds, especially after several consecutive production seasons. Using larger mesh traps in overcrowded ponds will only make matters worse by failing to thin the population of smaller, stunted crawfish. In this case, the need is to focus on managing the pond long-term to prevent overpopulation. Also you can grade the catch into two or three size grades setting an appropriate price scale for each grade.

Now if the pond is not overpopulated and the crawfish are not stunted, but they are small because they have not yet had time to grow to a desirable market size, there are a couple of management options you can use to increase the size of crawfish in your traps. The first option is to increase the soak time (the time the trap is in the water between baiting and emptying it) from 24 hours to 48 hours or even 72 hours. In other words, run your traps every other day, rather than daily. Smaller crawfish have more time to find their way out of traps before you empty them with a short soak time. Your catch will be reduced with a longer soak time (every-other-day trapping) but the size of crawfish will be larger. A second option is run the traps daily for three or four consecutive days and cease harvest for a few days. This often results in slightly larger crawfish being caught over the season with a minimal reduction in over-all yield when compared to trapping six or seven days per week. You can also combine these options.

To make a long answer short, using a 7/8-inch mesh can potentially help increase crawfish size but it is not a solution if the pond is overpopulated. If the pond is not overcrowded consider every-other-day trapping to increase crawfish size, or trap three to four days per week to give the crawfish some additional time to grow.




Size Classes of Crawfish
A crawfish population with three different age (size) groups.
Red swamp crawfish and white river crawfish usually produce multiple size (age) classes each production season, especially in permanent (single crop or monocrop) crawfish ponds. This simply means that females do not hatch their eggs and release their young all at one time; rather, young crawfish are released in most months that a pond is flooded, but with definite peaks of young being released in fall and winter. Distinguishable size classes that are found in crawfish ponds by mid-winter ( January/February) reflect the emergence of mature female crawfish from burrows with their eggs or hatchlings following flood-up and major rainfall events during October, November and even December. Under ideal conditions, from 3 to 5 different size (age) classes of juvenile crawfish would be observed by late December/January. 

The interaction between early crawfish (juveniles that enter the pond in September/October) and later hatched crawfish (juveniles that enter the pond in November/December) are not understood very well. In general, ponds with low densities of crawfish tend to produce larger crawfish while ponds with excessive reproduction and a lack of food often suffer from stunting prior to the end of the harvest season. 

To examine the effects of successive waves of juvenile red swamp crawfish recruitment on overall production and yield Dr. Greg Lutz with the LSU AgCenter’s Aquaculture Research Station stocked a number of outdoor tanks at the station (with soil, rice planted for forage and filtered pond water to eliminate predators) as follows: (1) some tanks were stocked with hatchlings right off the female on Oct. 1 at three per square yard, which reflected a low density, single recruitment class of crawfish; (2) some tanks were stocked on both Oct. 1 and Nov. 1, with both stockings at three per square yard for a total of six per square yard, and this reflected a low to moderate crawfish density, with a primary and secondary recruitment classes; and (3) some tanks were stocked with juveniles on Oct. 1, Nov. 1, and Dec. 1, all stockings at three per square yard for a total of nine per square yard, which reflected a moderate crawfish density, with primary, secondary and tertiary recruitment classes.

The presence of additional juveniles stocked in November (secondary wave of recruitment) and November/December (secondary-plus-tertiary waves of recruitment) resulted in nearly a 55 percent increase in crawfish yield (840 pounds per acre) compared to those pools stocked only in October (540 pounds per acre). Additionally, the multiple stockings of crawfish had no effect on the average size of crawfish harvested, which averaged about 19 count per pound in all three systems. This simple study shows the importance that November and December juvenile recruitment waves have towards contributing to the overall crawfish yield and potential profitability.


Last Updated: 10/21/2013 10:36:07 AM

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