Evaluation of the FVCOM modeling system to map the far-field dispersal of aquaculture waste

Description

Particulate aquaculture wastes, such as fish feces and feed pellets can accumulate beneath and near farm operations. Near-field waste accumulation is relatively well understood and can be predicted using depositional modelling tools such as the depositional model known as "DEPOMOD". Far-field distribution (i.e., distribution of wastes a distance away from the farm sites) and potential environmental effects of particulate waste and material that is re-suspended from beneath aquaculture cages is more complex and difficult to predict. With increasing concerns over the potential far-field effects of aquaculture, including cumulative effects and ecosystem interactions, it is necessary to be able to predict the quantity and range of this dispersal. The goal of this study was to develop a coupled hydrodynamic-sediment (i.e., particle) transport model capable of mapping the far-field dispersal of aquaculture wastes from a single farm site in southwest New Brunswick using the Finite Volume Coastal Ocean Model (FVCOM).

The hydrodynamic component of the FVCOM model has been used and validated for ocean currents in southwest New Brunswick. Additionally, the particle tracking component of this model, for use with passive particles, has been successfully employed to infer the movement of and the dispersal of dye which is similar to therapeutant transport. The fully coupled hydrodynamic-sediment transport model adds active particle transport by defining variables such as settling velocity, critical erosion shear stress, and erosion rate, which are necessary to predict the deposition and transport of aquaculture waste. To develop the model, parameters obtained from previous and current research on the transport dynamics of aquaculture waste were used. The model was validated using site specific data collected from a salmon aquaculture site in southwest New Brunswick.

The examination of this proof of concept modelling project helps facilitate improved predictions regarding the transport of wastes generated from aquaculture operations and consequently the potential environmental interactions associated with aquaculture operations in the far-field. This provides managers and regulators with the information needed to assist in decision making regarding the monitoring and/or mitigation of far-field wastes associated with aquaculture operations and for informing decisions on where to locate potential new aquaculture sites.

Findings

Presence of salmon aquaculture cage structures can cause changes in the tidal currents both in the whole water column and in the horizontal direction.

The sediment (particle tracking) module in FVCOM was configured using field data and run using a single size class of sediment representative of naturally settling and very small aquaculture waste particles. The model revealed that this material could be transported over 2 km away from fish cages and into the far field before settling. Model results also showed that the existence of fish cages were able to significantly change the local current field and the erosion of the bottom sediment beneath the cages. Optimal netting and depth of the fish cages could significantly increase the water velocity and bottom shear stress that could speed up the removal of wastes.

Publications

Wu, Y., Chaffey, J., Law, B., Greenberg, D. A., Drozdowski, A., Page, F. and Haigh, S. 2014. A three-dimensional hydrodynamic model for aquaculture: a case study in the Bay of Fundy. Aquaculture Environment Interactions5:235-248. DOI:10.3354/aei00108.

Program Name

Program for Aquaculture Regulatory Research (PARR)

Year(s)

2012 to 2014

Principal Investigator(s)

Brent Law
Habitat Sedimentologist, Fisheries and Oceans Canada, Bedford Institute of Oceanography, Maritimes Region
Email: Brent.Law@dfo-mpo.gc.ca

Yongsheng Wu
Research Scientist, Fisheries and Oceans Canada, Bedford Institute of Oceanography, Maritimes Region
Email: Yongshen.Wu@dfo-mpo.gc.ca

Terri Sutherland
Research Scientist, Fisheries and Oceans Canada, Centre for Aquaculture and Environmental Research, Pacific Region
Email: Terri.Sutherland@dfo-mpo.gc.ca

Team Member(s)

David Greenberg, Research Scientist, Fisheries and Oceans Canada, Bedford Institute of Oceanography (BIO), Maritimes Region

Jason Chaffey, Fisheries and Oceans Canada, Bedford Institute of Oceanography, Maritimes Region

Adam Drozdowski, Physical Scientist, Fisheries and Oceans Canada, Bedford Institute of Oceanography, Maritimes Region

Fred Page, Research Scientist, Fisheries and Oceans Canada, St. Andrews Biological Station, Maritimes Region

Susan Haigh, Physical Scientist, Fisheries and Oceans Canada, St. Andrews Biological Station, Maritimes Region

Randy Losier, Technician, Fisheries and Oceans Canada,  St. Andrews Biological Station, Maritimes Region