Population Biology and Production of the Red Swamp Crayfish Procambarus-Clarkii (girard) in the Lower Mondego River Valley, Portugal

The population of Procambarus clarkii from the lower Mondego River valley, Portugal, was studied for 13 months. Population structure was analyzed and 7 cohorts were identified. The main recruitment period occurred from the second half of October to the end of November, but juveniles were found throughout the year. Tracking recognizable cohorts along size-frequency distributions from successive sampling dates allowed an estimation of growth parameters in order to calibrate a growth model incorporating seasonal adjustments. Average growth rate was estimated at 1.16 mm of total length per week. Production was estimated at 27.22 g m-2 per year, the average biomass at 5.4 g m-2, and the P/B ratio at 5.03. Females outnumbered males throughout the year and the average sex ratio was 0.24.