Industry wide, crawfish yields for the 2005-06 production season have been abnormally low. This is especially true for those using the production strategy whereby crawfish are cultured behind rice in a field rotation approach. This strategy, involving most of the acreage devoted to crawfish production in Louisiana, is most susceptible to crawfish population adversities because population densities are typically lower than in ponds permanently dedicated to crawfish production. When crawfish are not cultured in the same field (pond) during consecutive production seasons, there is little opportunity for the build-up of populations and development of a wide range of reproduction cycles within the population – both are aspects that tend to mitigate adverse effects on populations. Therefore, unfavorable weather patterns or other environmental conditions that impact crawfish broodstock survival and/or reproduction generally have a greater impact on crawfish production systems that employ the field rotation approach. By all perspectives, the current drought in Louisiana began during the summer of 2005 and persisted through the fall, with the exception of some short-lived rains associated with one or both hurricanes.

Prolonged summer drought when crawfish are confined to burrows (where they reproduce) can hamper reproduction if residual water within the burrows is lacking. If the drought is severe enough and burrows completely dry out, massive mortalities of broodstock can result. Drought during the fall, at a time when crawfish are emerging from burrows with young, can also hamper production by preventing or delaying emergence from burrows. Crawfish remain trapped in burrows until the hardened dirt plug at the entrance of the burrow is sufficiently softened by pond flooding or rainfall. For crawfish burrowed in the levees above the normal water line of the flooded pond, timely rainfall is critical for the crawfish’s emergence – and limited rainfall amounts are often not enough to adequately soften the hardened plug.

Soil type, burrow depth, burrow location, and amount of water inside the burrow at the time of initial burrowing may play a role in how well burrowed crawfish respond to prolonged drought conditions. Because very little research exists regarding the burrow ecology of crawfish, especially as it relates to crawfish aquaculture, research at the LSU AgCenter is being focused in this area. One such project examined crawfish burrows in 2005 at the Rice Research Station in Crowley, approximately one month after pond draining. Two hundred sixty burrows were excavated and crawfish were retrieved, water volume and burrow depth recorded, and location of the burrow entrances were noted. The results are presented in the following tables.

Average burrow depths and water volume, by crawfish survival and number of burrow occupants, are presented in Table 1. Burrows containing female crawfish only are further organized according to burrow location and depth category in Table 2. It was surprising to observe that 45% of the burrows contained no living crawfish after such a short time following pond draining. Dead crawfish were generally associated with burrows containing no measurable water, and there was a strong positive relationship between the amount of water present and burrow depth. There was also a marked difference in average water volume, percentage of burrows with no measurable water, and crawfish survival between burrows initiated at or above the pond’s water line (likely pre-drain burrows) and those made on the pond bottom (post-drain burrows). Though the average burrow depths were similar, burrows found on the pond bottom (often near the base of the levee) generally contained much greater volumes of water, had fewer burrows without free water, and contained more living crawfish than burrows found at or above the water line on levees.

Though the implication of these findings with regard to burrow location is unclear, in the Crowley silt loam soil, burrow depth and water volume appear to be highly correlated; and the volume of water found in burrows soon after burrowing may play a significant role in the ultimate survival of reproductive female crawfish within the burrow. It was surprising to observe high mortalities in burrows within the first month of summer drawdown. These findings strongly implicate summer/fall drought as a significant factor in negatively impacting crawfish reproduction and subsequent yield, at least on silt-loam soils, and may help to explain the reduced yields reported, following the unusually dry conditions during 2005 in Louisiana.

Table 1. Aspects of burrow ecology relating to crawfish extracted from burrows following pond draining in experimental crawfish production ponds. Information is organized by crawfish burrow occupancy number and survival status.

¹11 of the 87 burrows contained male crawfish.
² Consisted of a male crawfish.
³All burrows containing 2 crawfish consisted of 1 male and 1 female.

Table 2. Observations obtained from burrows with female crawfish only, segregated by location of burrow and burrow depth.

¹ Averages are weighted averages and not simply grand means from each depth category.