Effect of Levee Reconstruction and Rainfall on Crawfish, Procambarus clarkii Emergence from Burrows

Abstract

Cultured red swamp crawfish, Procambarus clarkii in the southern United States burrow (usually in pond levees) to reproduce and to survive the period when ponds are dry (summer). When necessary, pond levees are renovated during the summer between production seasons. Little is known regarding the impact of levee maintenance on crawfish survival; therefore, this study was undertaken to gain some insight concerning this common practice. Crawfish burrows in pond levees were identified, marked, and mapped prior to the summer drawdown in 1997 and again in 1998 (total n = 849). Half of the levees containing the marked burrows were renovated according to standard industry practices and constituted the experimental treatment in the first part of the study. Crawfish emergence from burrows was monitored after flood-up and correlated to rainfall events. In the second part of this study, burrow entrances were individually disturbed (in 1997 and 1998; n = 80) to simulate levee renovation. The upper 15 cm of the burrow and surrounding soil was dug up and replaced with tilled soil. Additional spoil (tilled soil) was deposited on top at two levels (15 or 30 cm). The spoil on half of the burrows was compacted, yielding treatments in a 2 (level of fill) X 2 (compacted or non-compacted) factorial arrangement. Burrows were monitored after pond flood-up for evidence of crawfish emergence.

After adjustments in the 1997 data due to misidentification of some burrow entrances at time of marking, it was determined that only 55% of crawfish in non-reconstructed levees emerged during the fall. Thirty-eight percent of crawfish (or 31% less) emerged from reconstructed levees. Emergence from non-disturbed levees in 1998 was 70%, with a 13% reduction associated with reconstructed levees. Crawfish emergence from simulated levee reconstruction in the second part of the study averaged 35% for 1997 and 58% for 1998 with no significant differences associated with either level of fill or compaction. However, the lower level of fill was consistently associated with a higher percentage emergence. Emergence was positively correlated with rainfall events for both years; however, the correlation coefficients (r = 0.59-0.65) were only significant (P < 0.05) for 1998, which had 226% more rainfall than the same period in 1997. The positive correlation of crawfish emergence with rainfall events may help explain why early recruitment and early harvests are not always associated with early flooding.

Key Words:

• Crawfish
• burrows
• emergence
• rainfall
• levee reconstruction