USE OF A NATIVE PREDATOR TO CONTROL OVERCROWDING IN WARM-WATER POLYCULTURE PONDS - SIMULATION OF A TUCUNARE (CICHLA-MONOCULUS) TILAPIA (OREOCHROMIS-NILOTICUS) SYSTEM
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In this paper we describe an ecologically mechanistic simulation model representing the use of native predators (tucunare, Cichla monoculus) to control overcrowding of the primary culture species (tilapia, Oreochromis niloticus). The model consists of a prey submodel representing population dynamics and growth of tilapia, a predator submodel representing the predation process and subsequent population dynamics and growth of tucunare, and an economic submodel that calculates total net revenue. Simulated harvest weights of tilapia and tucunare were not distinguishably different from field observations, although tilapia weights were overestimated slightly. Results of sensitivity analysis suggest that the model could benefit most from refined estimates of tilapia growth rate and a better understanding of the dynamic size relationships between predator and prey that determine prey availability. Simulation of 21 different management scenarios suggests that stocking 10 tucunare weighing either 2 g or 10 g yields the highest total net revenue at the earliest harvest data. Stocking 20 tucunare weighing either 2 g or 10 g yields only slightly less total net revenue, but postpones harvest time by 3 weeks. Given the complexity of predator-prey relationships within polyculture systems, the interpretation of field observations on fish survival and growth can be enhanced greatly when viewed within the framework of an ecological model. From a management perspective, ecological models provide a means of explicitly relating pond production, and hence net revenue, to the underlying ecological processes that ultimately drive system dynamics. 1994.
