Ecological Modelling 123 (1999) 5 – 16 CRISP (crayfish and rice integrated system of production): 2. Modelling crayfish (Procambarus clarkii ) population dynamics P.M. Anasta ´cio a, *, S.N. Nielsen b , J.C. Marques c a IMAR, Department of Ecology, Uniersity of E ´ ora, Apartado 94, 7001 E ´ ora codex, Portugal b Royal School of Pharmacy, Enironmental Chemistry, Uniersitetsparken 2, DK2100 Copenhagen, Denmark c IMAR, Department of Zoology, Uniersity of Coimbra, 3000 Coimbra, Portugal Accepted 12 October 1998 Abstract 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. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Crayfish; Procambarus ; Model; Population dynamics; Integrated production www.elsevier.com/locate/ecomodel 1. Introduction The Louisiana Red swamp crayfish, Procam - barus clarkii, is an exotic species in Spain and Portugal. In both countries, soon after its intro- duction, crayfish populations increased without control, invading most of the rice fields and wet- land areas (Correia, 1993). To prevent damage to rice crops farmers have tried to get rid of crayfish by means of xenobiotic chemicals. Unfortunately, in environmental terms, this was not the wisest decision. A better solution is the use of crayfish as * Corresponding author. Tel.: +351-266-745385; fax: + 351-266-709498. E-mail address: anast@evunix.uevora.pt (P.M. Anasta ´cio) 0304-3800/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII:S0304-3800(99)00164-7