WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2013 53 (CONTINUED ON PAGE 52) Calibrating ShellGIS A demonstration site was chosen for ShellGIS development in the upper Damariscotta River, Maine, USA, where Eastern oyster Crassostrea virginica is cultured in surface and bottom systems. To populate the GIS system, historical data and field data collected from 2010-2012 were used to provide drivers for the hydrodynamic model (depth, tidal elevations, water velocities) and the shellfish growth model (water temperature, salinity, chlorophyll a, TPM, POM, dissolved oxygen, POC, PON, shellfish growth rates and mortality). Water samples were collected at the surface and near the bottom throughout the growing season and field and modeling studies of food supply and demand in bottom and tray culture were performed. ShellSIM was calibrated for Eastern oysters by measuring feeding response in flow-through biodeposition chambers (Fig. 2). Care was taken to ensure that measurement of environmental variables used as forcing functions in ShellSIM represented the exact conditions actually experienced by shellfish at sites where shellfish growth was monitored. Measurements confirmed that Eastern oysters make use of detrital organic matter and living phytoplankton (Fig. 3) and with a similar form of digestive function as other bivalve species. ShellSIM was calibrated for Eastern oysters using measures of feeding behaviour and literature values for responses to temperature, salinity and other variables. Applying the resulting set of parameters for this species within ShellSIM’s standard set of functional interrelations, growth was simulated to < 5 percent error across full ranges of environment variability and variability in normal culture practices in the Damariscotta River and Long Island Sound (Fig. 4). ShellGIS Output The high-resolution flow results (50-m grid or better) and particle depletion modeling (depending on culture strategy and stocking density) make the software useful for running “what-if” scenarios on the modeled domain, rather than engaging in “trial and error” aquaculture. The software allows queries on a range of practical issues that are important to potential culturists: • Where is the best place to grow shellfish in a particular bay or region? • What is the effect of seed size, time of year and planting density? • What is the growth rate of the selected species? • What are the results in weight, length or profit? One of the most useful aspects of the ShellGIS system is the use of STEMgis2 software because STEMgis stores and presents data over time and over depth (4 dimensional) and presents data in 3D viewers and video animation, as well as in traditional static layers. The ShellGIS team also created customized user interfaces because many GIS or ecosystem modeling software packages present a confusing array of user inputs and options. To improve the user interface, meetings with shellfish farmers resulted in the addition of new oyster growth prediction capabilities to the software, including: • What is the difference between a warm year and a cold year? • What is the difference between tray or bottom culture at a given site? • What is the difference between a wet and a dry year? • Is it more profitable to grow more smaller oysters than fewer larger ones at a site? • What are the effects of time of year of seeding on time to market size at different farm sites? Examples of ShellGIS runs based on frequently asked questions by oyster growers were presented at the NACE meeting in Groton, Connecticut (2012) and the NSA/WAS meeting in Nashville, Tennessee (2013). FIGURE 3, LEFT. Relation between total organic absorption (mg/h/g) and the relative ingestion of detrital and phytoplankton organics (mg/h/g) in the Eastern oyster Crassostrea virginica. FIGURE 4, ABOVE. Comparisons of Eastern oyster growth simulated by ShellSIM with growth observed (mean ± 2 SE) throughout normal culture practiced in both the Damariscotta River, Maine, and Long Island Sound, Connecticut.
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