Effects of water renewal estimates on the oyster aquaculture potential of an inshore area

Tidal and wind renewal of water in the coastal zone is important in the transport of natural and anthropogenic particles and solutes. Models of these systems require detailed parameterization of exchange processes. Renewal of seston food supplies for cultured suspension-feeding shellfish is one such application. This study examines the sensitivity of food limitation estimates of an inshore region for shellfish aquaculture to the methods used in calculating the region's water renewal time. The region is the Indian Island oyster culture site in the Richibucto estuary, New Brunswick, Canada, and the methods considered are the volume advection and the local conservative tracer methods. In both cases, water renewal is calculated from field time series measurements of hydrodynamic parameters and outputs of coupled hydrodynamic and advection-dispersion three-dimensional (3D) numerical models. A comparison of oyster food demand and supply is then made to estimate the food limitation risk in the region using field measurements of biological parameters and the renewal times previously estimated. It is found that water renewal by tides is efficient but it can be cancelled altogether by meteorological forcing. Contrary to the conservative tracer method, the tidal prism method proves to be inadequate when estimating water renewal in estuarine tidal channels and was replaced by another volume advection method. The preliminary results obtained using the depletion index estimates indicate that the Indian Island region could sustain a high oyster biomass. These simple calculations also show the importance of water renewal estimate for carrying capacity studies. Hence, the tidal prism method or other volume advection estimates should be used with great caution or be avoided altogether in such studies.