CRISP (crayfish and rice integrated system of production): 2. Modelling crayfish (Procambarus clarkii) population dynamics

An ecological sub-model of crayfish (Procambarus clarkii) population dynamics is presented for integration into the CRISP (crayfish and rice integrated system of production) series of models. The present structure is directed towards simulation of crayfish population responses under different human interventions, namely different capture rates. The crayfish population was subdivided into seven age classes of 80 days, each one constituting a state variable. The increase in weight for each 80-day period was considered dependent on the temperature, the oxygen level and the water level. Mortality was assumed to be dependent on the dry weight of the crayfish and regulated by the total crayfish biomass. Food, water and oxygen content of the water were considered to be non limiting. Total crayfish biomass and total wet weight of crayfish captures were very sensitive to both the temperature for maximum growth and the mortality rates. Our most optimistic simulation, with a 50% decrease in the mortality rates, resulted in a fourfold increase in captures, from 230 to 917 kg ha^-1 per year. Without capture, a value of 121 kg ha^-1 was simulated for the average crayfish biomass, which is close to the 124 kg ha^-1 obtained with crayfish capture. Our simulated average crayfish biomass was approximately 120 kg ha^-1 in a natural situation, which lies inside the reported ranges from areas at approximately the same latitude.