Dynamics of commercial size interval populations of female redclaw crayfish (Cherax quadricarinatus) reared in gravel-lined ponds: A stochastic approach

The objective of the present study was to establish the impact of monosex-female redclaw crayfish (Cherax quadricarinatus) culture in gravel-lined ponds, by using a stochastic approach to analyze production dynamics for the 40-60 g, 61-90 g and> 90 g commercial-size intervals. After growing female redclaw crayfish 17 weeks in 2500 m(2) gravel-lined ponds stocked at 6 females m(-2), mean final weight was 80.53 +/- 0.70 g, survival was 76.2 +/- 1.7% and FCR was 0.82 +/- 0.10. Overall, yields averaged 0.26 t ha(-1), 2.12 t ha(-1) and 0.99 t ha-1, respectively, for the 40-60 g, 61-90 g and> 90 g size intervals. This resulted in a mean total biomass of 3.39 t ha(-1) and a commercial biomass of 3.3 t ha-1. Values of the coefficient of variation of total commercial biomass indicated a maximum certainty in production after 10 weeks, when percentages of recruitment of the 40-60 g and 61-90 g size intervals were similar. The contribution of the > 90 g size interval was negligible, and the total composition of the commercial population was more homogeneous. The sensitivity analysis showed consistency of the simulation model. After 10 weeks, variability of the commercial biomass is particularly influenced by the rate at which mean individual weight (w(t).) changes from its initial value to its final value (k). In contrast, after 17 weeks the variability of k was not relevant in determining the variance of commercial biomass, because the influence of k progressively diminishes as the final weight of crayfish is approached. Results from the Monte Carlo simulation indicated that, when increasing sample size from one pond to 100 ponds, variability in production forecasts was reduced 89.8%. The present study demonstrates the feasibility of monosex-female redclaw crayfish culture in gravel-lined ponds. It also shows that the stochastic approach used to analyze production dynamics for the 40-60 g, 61-90 g and> 90 g commercial-size intervals is an important tool to evaluate the impact of size classes on total production and commercial yields. According to our results, we recommend an initial stocking density of 6 organisms m(-2) for commercial monosex grow-out of females in gravel-lined ponds.