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Crawfish News March 2012 (Vol 5, No 1)

Crawfish News March 2012 (Vol 5, No 1)
Crawfish News March 2012 (Vol 5, No 1)

Summer Fall Rainfall
Figure 1. Monthly average rainfall in Lafayette, La., for selected portions of 2010 and 2011 compared to the long-term average (“norm”). Source: Louisiana State Office of Climatology.

The 2011-2012 crawfish season, like last year, got off to a slow start. Reports from the field indicated this year’s early season harvest was below last season’s early catch, and that 2010-2011 early crop of crawfish was considered poor.

So what was the most likely cause for the slow start to this year’s farm-raised crawfish crop? We believe “drought” from June through November was the overriding factor in reducing the early season farm-raised harvest statewide.

LSU AgCenter research has shown insufficient rainfall during summer and fall can reduce crawfish production. This happens in a couple of ways.

First, crawfish need an adequate supply of water in the bottom of burrows for the females to survive. If a burrow cracks open and the water evaporates and is not replenished by rainfall, crawfish most likely will die. If the burrow remains sealed with 100 percent humidity, but if no standing water is at the bottom of the burrow, the female may live, but the eggs she lays will not hatch. So it possible to have both death loss and reduced spawning of females from drought conditions in summer and early fall.

Second, rainfall, particularly in October, is critically important in softening the burrow plugs so females with young can emerge from the burrows. Dr. Ray McClain, in studies conducted at the LSU AgCenter’s Rice Research Station, showed rainfall was more important to female survival and egg hatching than the depth of the water table. Many crawfish do not burrow to the depth of the water table as was previously thought. McClain found rainfall in October through December is needed to soften the hard dirt plug that seals the burrow. An exceedingly dry October delays emergence of the females with young because they can’t escape from their burrows. Many farmers who have been in business for years are familiar with seeing females with eggs or young attached to the tail emerging from burrows following heavy thundershowers in September, October and November. Meager rainfall in October delays emergence of the females with young and thus delays the crawfish crop.

How does this assessment match with summer-fall-winter rainfall the past two years? The monthly rainfall at Lafayette from June through December 2010 and June through December 2011, along with the historical “norm” (average rainfall), are presented in Figure 1. For 2011, the cumulative rainfall from June through August was 40 percent below normal, and for August, a month when many eggs are laid, rainfall was 60 percent below norm (Figure 1).

During the first few days of September 2011, Tropical Storm Lee delivered excessive rainfall over a few days, which likely caused some crawfish to emerge early, temporarily disrupting the reproductive cycle. In October, when many females with young were ready to leave burrows, rainfall was only a ¼-inch – compared to the norm of 4 inches. With so little October rainfall burrow plugs could not be sufficiently softened for females with young to emerge. Sufficient rain to allow for significant numbers of females with young to emerge from burrows did not occur until November.

Rainfall in September and October of 2010 was also much below normal (Figure 1). As in 2011, sufficient rainfall to allow significant emergence of females with young did not occur until November 2010. This is why the 2010-2011 season got off to a slow start.

Because many young crawfish did not enter ponds until mid- or late November, and it takes three to four months for juveniles to grow to harvest size, the bulk of this year’s farm-raised crawfish crop will not begin to be caught until late February or March.

So why would crawfish not emerge, even under drought conditions, when most ponds/fields are flooded in mid-September through October? The reason is that most mature females, which produce the bulk of season’s late fall and winter crop, are “early” burrowers in the spring, meaning they burrow above the water line in April/May/June when ponds are at full flood (maximum depth). Because these crawfish burrowed above the maximum water depth, most are not flushed out when ponds are filled in September/October. Rainfall is needed to soften the burrow plugs and allow them to exit the burrow and enter a pond filled with water.

A few other factors likely play into the lack of an early crawfish crop for individual farmers in various areas of the state. For farmers who rely on surface water, the water supply in many canals and drainage ditches was limited, and some ponds could not be flooded in October because of a lack of water. Other farmers delayed flooding because of high fuel prices (high pumping costs) and waited until later in the year when temperatures cooled and rainfall could reduce the cost of pumping.

In the large crawfish producing parishes of Vermilion and Jefferson Davis, ponds located near the coast had to deal with issues of salty water. Some of these farmers delayed flooding their ponds until November – after sufficient rainfall occurred to dilute the salt content of their water supplies.

For some farmers, another factor associated with a meager early crawfish crop dates back to the end of last season. Last spring and summer (2011), crawfish were harvested into June and July in some ponds because prices remained high and demand remained strong. Late-harvested ponds may have had fewer holdover crawfish to catch this past November and December. Much of the early catch in November and December involves holdovers from the previous spring.

In addition, some ponds may have been restocked later and with fewer crawfish than the AgCenter recommends. The later crawfish are stocked, the greater the stress to females from high temperatures. Thus, there is higher likelihood crawfish reproduction will be negatively affected.

Of importance, many farmers were seeing the presence of small juveniles in their ponds by late November. The average temperatures this January (58 degrees Fahrenheit) was about 6 degrees F higher than the January norm (52 F). This has allowed for more rapid growth of young crawfish that emerged in November.

Icing Crawfish

As the crawfish catch starts to pick up, there are some reports of significant death loss of crawfish being held in coolers awaiting sale.

While we transition from the mild winter to spring, it is important that crawfish be handled properly from the time they are caught through transportation to their end destination, whether that be a wholesaler or direct sale to a restaurant.

High mortality of crawfish after being caught this time of the year usually can be attributed to three major factors: (1) low oxygen in ponds, (2) sacks of crawfish drying out from being left on levees too long before being transported to a cooler and (3) some crushing of tender crawfish in the sacks as they are handled and transported.

Let’s review basic handling and transport recommendations for sacks of live crawfish to ensure they get to your buyer in the best condition possible:

Strive to Maintain Good Water Quality in Your Ponds

Retailers always want to purchase from producers/wholesalers who have a reputation of supplying live crawfish that have a long shelf life.

Long shelf life in the cooler starts with the physiological condition of the crawfish when they are caught and sacked. Crawfish caught in ponds with adequate oxygen levels are not stressed to any large degree and that will significantly increase shelf life. (Managing oxygen concentrations in your crawfish pond is discussed below.)

Keep the Crawfish Wet, Cool and Covered

Do not let sacks of crawfish dry out!

Do not leave sacks sitting in the sun or exposed to the wind for very long, even in cool weather. Do not let sacks lie in water in bottom of the boat. Cover the crawfish with a wet tarp to keep them cool and moist. Avoid putting sacks in direct sunlight if possible. Do not allow the gills of the crawfish to dry out as this significantly reduces shelf life. Use a tarp in the boat, for sacks of crawfish placed on the levee for later pickup and in the bed of the truck when transporting crawfish to the buyer.

If crawfish are stored in a cooler, the temperature should be 38 to 45 degrees Fahrenheit and the crawfish should be kept moist by placing crushed ice on top of the sacks. As the ice melts, water will drip through the sacks, keeping the crawfish moist. If ice is not available, spray the sacks with water as needed to keep them moist.

If the weather is warm and you are transporting crawfish in the back of your truck, put ice on them to keep them cool and prevent them from drying out.

Don’t Crush the Crawfish

Most crawfish that are being harvested at this time are “tender” (they have thin shells) and they are highly susceptible to being crushed if the sacks are tossed around or stacked too high.

Avoid rough handling (throwing or bouncing the sacks) or stacking the sacks too high when crawfish are tender because those mistakes can crush the shells and cause death of crawfish, particularly in sacks at the bottom of the stack. If you see a clear, sticky, jelly-type substance on the outside of sacks, this is coagulated crawfish blood (it is clear or slightly opaque in color) that was released from crushed crawfish.

Make Sure the Sacks Are Clean

Take care to ensure crawfish are not bagged with grass, bait, turtles or mud in the sack. Keep the floor of your boat and the bed of your truck clean to prevent contamination of sacks from oil, fuel, grease or the dirty water that is bound to accumulate. Consider placing sacks of crawfish on a pallet in the boat. Store empty sacks in a clean container until you need them.

With an early spring having already arrived, anticipate that water quality in your ponds will decline. In other words, anticipate that you likely are going to have low oxygen conditions to deal with.

When the water warms and the ponds still contain large amounts of decomposing vegetation, oxygen levels will decline as decomposition of the vegetation increases. Spot check oxygen in the ponds at least a couple of times a week.

Prolonged oxygen concentrations less than 1 part per million for two to three weeks are extremely detrimental to the well-being of the crawfish. If you observe crawfish clinging to vegetation or traps, while lying on their sides at the water’s surface, oxygen is at a critical level. Growth of young may be reduced, catch may decrease and shelf life of live crawfish is shortened.

If needed, increase oxygen concentration by replacing oxygen-depleted water with fresh, oxygenated water, but base the need for pumping on oxygen measurements. Why pay for diesel and electricity to run your pumps and flush your ponds when it is not needed? An article titled “Measuring Oxygen in Crawfish Ponds” is available on the LSU AgCenter’s crawfish website, and the link to that site is provide toward the end of this newsletter. Or if you are not “computer savvy,” visit your parish LSU AgCenter Extension Service office and ask them to a print a copy of the article for you.

Trapping Crawfish

Our recommendations on trap density (number of traps per acre) are based on your projected crawfish harvest in pounds per acre, and the recommendations assume you’ll be using pyramid traps with 3/4-inch square-mesh welded wire and trapping, on average, three to four days per week.

Use 10 to 15 traps per acre for low-density/lower-yield ponds. Low-density crawfish ponds are often 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 rotations. These ponds typically yield 400 to 600 pounds per acre in a normal year.

Use 18 to 22 traps per acre for high-density crawfish ponds. High-density crawfish ponds usually are those in which the pond is managed solely for crawfish and crawfish are produced in the same pond or field year after year. These ponds can yield as much as 700 to 1,200 pounds per acre in normal years.

If you happen to still be using less-efficient 3/4-inch hex-mesh pyramid traps, 7/8-inch square mesh welded wire or even the old 2-flue stand-up pillow traps, increase the number of traps by 20 percent.

Spacing between traps and rows to obtain a specified number of traps per acre can be found in Table 8.2 (page 35) of the Louisiana Crawfish Production Manual (LSU AgCenter Publication 2637). If you don’t have copy of the manual or you need a replacement copy, contact your parish LSU AgCenter Extension Service office to obtain a copy, or order one off the LSU AgCenter’s crawfish website. If ordered from the website, the cost is $ 1, plus postage.

As a producer, you have control over all aspects of bait management – how much you add per trap, how frequently you run your traps and how many traps are in your pond.

On a 100-acre operation with 15 traps per acre and if traps are run 70 days during a season, you will have baited traps about 100,000 times during that season. Saving just a few cents per trap each time it is emptied can provide significant savings in bait expenses, particularly on large crawfish farming operations.

Fish or Formulated? Use fish bait (pogy, shad, carp, buffalo, herring, slicker or similar fish) when water temperature is less than 65 to 70 degrees Fahrenheit. That strategy usually will take you into March and maybe early April.

When water temperatures exceed 70 F to 75 F and forage begins to become depleted (usually late March to early April in south Louisiana), manufactured bait becomes more cost-effective because it catches better and is cheaper. Set some test traps or a row of test traps with manufactured bait to see if it is time to make the switch from fish to manufactured bait.

At water temperatures of 65 F to 75 F a combination of fish and formulated bait added to traps in about equal portions can increase catch as much as one-third over fish alone or formulated bait alone. The logistical inconvenience of handling two baits at the same time in harvesting boats must be considered when employing this strategy but it is effective.

How Much Bait? Use about 1/4 pound of bait per trap when water temperatures are cool and the density of harvestable size crawfish is low. When waters warm and the crop of harvestable crawfish increases, or if little or no bait residue remains in the traps in an overnight set, increase the amount of bait to 1/3 pound per trap.

Using more bait per trap may increase your catch in a pond with a high population of crawfish, but the additional catch usually is not enough to compensate for the added bait cost.

Keep track of bait use as follows: a 50-pound bag of manufactured bait is sufficient to bait 150 traps (50 pounds bait ÷ 0.33 pound per trap = 150 traps). If you are only baiting 100 traps, you’re using too much. A 60-pound box of fish should be sufficient to bait 180 traps (60 pounds fish bait ÷ 0.33 pound per trap = 180 traps).

Pay attention to the amount of bait remaining in traps when you empty them. If significant bait residue remains in the trap, the amount can be reduced. Do not dispose bait residue in the pond that you are trapping in, however, because that might reduce crawfish movement to freshly baited traps.

1-Day or 2-Day Trap Sets? Normally, traps are emptied after a one-day or two-day set (every other day). Both are effective and can be used in your trapping program.

Every-other-day trapping is effective in cooler water when using manufactured bait. It also has the advantage of catching larger crawfish, because smaller crawfish more easily escape from the trap the longer it remains in the water. A two-day set partially functions as an in-pond grading system.

If your pond is overpopulated with crawfish, however, you may need trap daily to reduce the population density and decrease the chance of stunting of your crawfish.

We do not recommend returning small crawfish caught in traps to the pond for further growth. It is better to sell them even at a reduced price. LSU AgCenter research shows less than half of crawfish returned to the pond will be re-caught, and even if they a caught again they will not necessarily be caught at a larger, more valuable sizes.

The LSU AgCenter’s website has a tremendous amount of useful information on a variety of topics in areas such as agriculture, natural resource, food and health, family and home and youth development. For those who may not be aware, there also is a crawfish section that is one of the most frequently visited pages on the LSU AgCenter’s website.

The Crawfish section of the website has information on just about all facets of crawfish and the crawfish industry. If you need information you can’t find on the crawfish page, or if you have other recommendations to improve the crawfish Web page, please contact us with your suggestions.
Last Updated: 3/2/2015 11:45:24 AM

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