Evaluation of Sampling Gear for Predicting Harvest Size, Yield and Incidence of Stunting in Crawfish Ponds.
Date of Award
Doctor of Philosophy (PhD)
Forestry, Wildlife, and Fisheries
Robert P. Romaire
Dip-nets, test traps and experimental drop samplers were evaluated for their potential to predict crawfish (Procambarus spp.) yields and size distribution at harvest. Field studies were conducted at the Rice Research Station, LSU Agricultural Center, Crowley, Louisiana, between 1991 and 1996 in 82 (0.16-0.2 ha) earthen impoundments. Fields were managed to simulate rice-crawfish systems typical of the southwestern and south-central Louisiana. Multiple linear regression analysis was used to determine the relationship among catch-per-unit-effort (CPUE) of sampling gear (alone and in combination) with respect to yield in weight (kg/ha), yield in number (crawfish/ha) and size distribution at harvest. Relative abundance of crawfish as determined by each gear was compared to size distribution at harvest to develop predictive capabilities for assessing the potential of ponds to yield sub-marketable ("stunted") populations. Ponds with recruitment during October to December were shown to yield 800 to 1,000 kg/ha, based on December dip-net sweeps of 0.25 to 1.5 crawfish/sweep or a December test trap catch of 0.5 to 11 crawfish/trapset. At higher sampling CPUE rates, yields began to decline. The CPUE of all three gear were statistically correlated to yield in number (crawfish/ha). Regressions models predicted a smaller size harvest with increasing number of crawfish caught per sample. Dip-net sweep models predicted $<$30% of total yield in weight would be $\ge$21g when mean monthly catch during November through February was $>$1.5 crawfish/sweep. Test trap critical thresholds for "stunted" populations ranged from $>$4 crawfish/trapset in November to $>$9 crawfish/trapset in February. Drop sampler models predicted "stunted" populations when catch exceeded 13 crawfish/m$\sp2$ during November through February. Multiple gear assessments within a pond did not produce a significant improvement over the predictive capability of the gear when used alone. An empirical relationship existed among the number of crawfish caught with one gear and the number of crawfish caught with another gear. This relationship changes as the season progresses due to the effect of size on vulnerability to different gear. Additional research is needed to evaluate the reliability of drop sampler devices to accurately reflect crawfish standing crop and biomass.
Avery, Jimmy Lee, "Evaluation of Sampling Gear for Predicting Harvest Size, Yield and Incidence of Stunting in Crawfish Ponds." (1997). LSU Historical Dissertations and Theses. 6536.