Modelling the population dynamics of an exploited, tropical fish species playing a fundamental role in aquatic ecosystems

The coporo, Prochilodus mariae, plays a fundamental role in aquatic ecosystems as a detritivorous species facilitating the flow of carbon to the rest of the ecosystem's food web. It is also one of the most exploited freshwater fish species. Fishing, pollution and environmental changes in the Orinoquia region of Colombia have considerably reduced its population size. We analysed the population dynamics of P. mariae during an annual river cycle, including extreme drought and flood scenarios, by means of a mathematical model and simulations. The model we propose is novel because it relates biological, ecological and environmental factors to the population dynamics, including reproduction, growth in size and biomass of fish, recruitment, predation, fishing mortality and river flow. The proposed mathematical model apparently gives an approximate description of the population dynamics of P. mariae for 2010 because a good fit of the model to the catch data of the species of that year was obtained. The simulations showed that the first 3 months of the year are crucial for the species because this is when it is most affected by a combination of fishing, biological factors which increase natural mortality (e.g. upstream migration and predation) and environmental factors (e.g. low river flow). Hypothetical scenarios show that local extinction could occur if fishing were to increase and river flow were to decrease.