HYDRODYNAMIC MODEL VALIDATION IN A CHILEAN EMBAYMENT: TOOLS FOR MODELLING FOOD DEPLETION IN MUSSEL FARMS  

Manuel Díaz1*, Gonzalo Olivares2, Diego Narváez3, Carlos Molinet1 and
Patricio A. Díaz1
 
1Programa de Investigación Pesquera & Instituto de Acuicultura, Universidad Austral de Chile, Puerto Montt, Chile
 2Ocean Applied Science Ltda, Puerto Varas, Chile
 3Departamento de Oceanografía, Universidad de Concepción, Concepción, Chile
 manueldiazgomez@gmail.com

In the recent years, there has been a growing global concern about the carrying capacity of coastal systems used for mussel aquaculture, including the Inner Sea of Chiloé (41.5º-43.5ºS) in southern Chile. This region supports almost 99% of the Chilean mussel (Mytilus chilensis) aquaculture, with annual productions of ~250,000 tons, placing Chile as the 4rd world's producer. Models for food depletion has been extensively used to estimate productive carrying capacity. Previously developed conceptual models have suggested that the water flow through the mussels' farms is an essential factor for optimal application of a food depletion model as a function of mussel loads and current velocities. In this study, we validated a hydrodynamic model in a southern Chilean embayment (Compu, Chiloé Island), used as input to move particulate organic material and therefore predict mussel production without negative effects in the growth rate and avoid non-sustainable practices.  

Surface current velocities were simulated with the Regional Ocean Modelling System (ROMS), which was forced by wind and tides, with horizontal resolution of 133-m and 32 terrain-following vertical levels. Validation was carried out with in situ observations recorded with an ADCP in Compu from 5 March to 3 April and from 14 May to 11 June 2014 and local winds recorded at the same time with a HOBO U30 Station.

The simulated hydrodynamic reproduced relatively well the circulation pattern in the Compu embayment (Fig.1). This model predicts the current velocities with a standard error of ±4 cm s-1 and 90% of the variance explained along the maximum variance axis (u along-embayment). Thus, the application of ROMS adequately predicts the movement of particles provided a reliable input information for modelling food depletion, increasing our capacity to find optimal conditions that maximize mussel's production.

Figure 1.  Simulated surface currents during flood (upper) and ebb (lower) tide in Compu embayment, Southern Chile.