Monitoring and simulating the operations and dissolved waste production of cobia fish farm off the coast of Cartagena, Colombia

Abstract

In 2008 the first fish farm in Colombia was constructed off Tierrabomba Island near Cartagena de Indias (10.3601 – 75.5966 NW). The farm was stocked with cobia, Rachycentron canadum. This species grows very rapidly, has high market value, and has been successfully cultured in the Caribbean. Three years after initial stocking of the cages, a study was begun to determine the farm’s effect on the surrounding environment. Monthly physical variables and nutrients in the water column were measured for eight months at three stations located in proximity of the cages (5, 30, 100 m) and a control point (1000 m). At each station, samples were collected and measurements were made at depths of 7, 15 and 30 m. Additionally, a current Doppler profiler was installed near the site and data were collected continuously. This information was input and analyzed with the AquaModel fish farm simulation software (www.aquamodel.org). This software consists of a system of coupled sub-models of fish physiology, hydrodynamics, water quality, dispersion of dissolved and particulate wastes produced by the farm, and the ecological transformations of these wastes within the water column. AquaModel’s 4-D simulation of farm operation and environmental impact is driven by the currents measured with the Doppler profiler as well as other field measurements such as water temperature, and the concentrations of oxygen, nutrients, and chlorophyll-a. The simulation indicated that the environmental impact of the farm was insignificant. Both the field measurements and simulation results show that there is rapid dilution of the total dissolved nitrogen downstream from the farm, and that the concentration of oxygen in the cages and in the ambient waters is above the 5 mg / L, more than sufficient to support rapid growth of the fish.