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Aquaculture Site Selection

Mussell raft and lines in Blue Hill Bay, Maine
Mussel Raft and Lines, Blue Hill Bay, ME

This article, authored by John Richardson (Blue Hill Hydraulics) and Carter Newell (Great Eastern Mussel Farms), summarizes their work in developing the Aquaculture Expert System, which is used to improve shellfish culture throughout North America and in the British Isles.

Site selection plays an important role in successful marine shellfish culture. It has been shown, for instance, that shellfish grow best when they are exposed to tidal currents within certain limits. Site selection and the knowledge of local site characteristics also affect mooring design and stocking densities.

To address the issue of site selection for aquaculture systems, a three-dimensional numerical modeling scheme for simulating flows through individual aquaculture units (e.g., floating rafts) and lease-sites was developed. The modeling approach, which uses FLOW-3D as its hydraulics engine, is capable of calculating nutrient uptake and transport, and can also be used to simulate larger-scale circulation patterns in coastal areas. This modeling scheme provides a comprehensive understanding of the near-field hydrodynamics of shellfish culture systems, and can be used to simulate the performance of a wide variety of different cultivation strategies in order to increase their productivity (e.g., rafts or other culture systems such as bottom, rack and bag, longline, and tray or basket systems).

The Importance of Aquaculture

It has been many years since the world's demand for seafood has exceeded its availability in nature. About half the world's wild fisheries have been exhausted by overfishing, driven principally by the combination of a growing population and increased consumer demand for fish as a healthy alternative to red meat.

Aquaculture, the process of rearing fish in captivity and managing both the fish and their environment to improve growth and reproduction, has the potential to pick up the slack. Today, farm grown finfish and shellfish supply 30% of all the seafood consumed worldwide, up from 10% just two decades ago. Aquaculture is one of the fastest-growing segments of global food production. (Source: Time, November 25, 2002). Typically, aquaculturists use floating cages or rafts to raise their stocks in estuaries and coastal areas.

This note is focused on marine shellfish culture. Click here for more detailed background information on the development of shellfish farming techniques in Maine.

Screeshot of the Aquaculture Expert System
Main input screen for the GUI.

FLOW-3D aquaculture simulation of phytoplankton
The calculated distribution of
phytoplankton with dual raft
aquaculture system

Aquaculture data collection
Field data collection

The Aquaculture Expert System

The Aquaculture Expert System is a comprehensive tool devised by the authors to assist shellfish growers with site selection, increasing productivity & yield and more. The system uses FLOW-3D to provide the hydraulic information required to calculate food availability within shellfish aquaculture systems based on site specific conditions and husbandry practices. As a result of its formulation, the expert system can be used to simulate flow through different types of aquaculture structures such as rafts, cages, and longlines.

Use of the Aquaculture Expert System has increased the productivity of farms in Maine, and the expert system is currently being used in Virginia, Connecticut, Washington State, and Ireland.

Typical studies with the Aquaculture Expert System involve in situ data collection and computer modeling. Results of the studies answer questions. How many shellfish can a water body support without slowing growth rates? What seeding densities should be used at a given location? Where aquaculture operations should be located to maximize growth? What is the best aquaculture practice to use within a given water body?

Studies with the expert system can require all of the following information depending on the scope of the analysis: bathymetric data (water depths in the vicinity of the aquaculture farm), hydrologic information (tidal records and estimates of river flows), water quality data (conductivity, temperature and chl-a versus depth measurements), and lease site information (layout, seeding densities, and raft design).

These data are used to produce computational models of aquaculture farms and surrounding waters. The models predict food concentrations within the aquaculture sites as well as current speeds and mussel growth rates. By performing a series of what-if simulations the effect of changes made to existing or proposed aquaculture operations can be evaluated.; For example, the graphics below show how different schemes for attaching ropes to aquaculture rafts can affect the amount of water that passes through the rafts (ref. Hardwood Island research study). Read about more cases where the Aquaculture Expert System has been successfully applied.

FLOW-3D CFD simulation of flow through aquaculture rafts
Flow through Aquaculture Rafts (colored by speed)

During the summer of 2005, further development of the Aquaculture Expert System is planned as part of the National Oceanographic and Atmospheric Administration's (NOAA) National Marine Aquaculture Initiative (NMAI). This research is designed to provide information regarding the effects of shellfish farms on the surrounding environment.

To aid in the environmental assessment of different types of shellfish culture, the Aquaculture Expert System will be used to determine the relative impact of each production method studied. Research sites for the project are located in Chesapeake Bay, Long Island Sound, and Puget Sound, and will involve the study of flows and shellfish growth in inter-tidal locations.

The NOAA project titled, 'Environmental and Technical Assessment of Alternative Shellfish Production Methods' is being managed by the Pacific Shellfish Institute (Olympia, WA) and includes researchers from Connecticut Sea Grant, the Massachusetts Institute of Technology, the Pacific Coast Shellfish Growers Association, and the Virginia Institute of Marine Sciences.

About the Authors

Development of the Aquaculture Expert System is being carried out by Aquaculture Productivity.

Aquaculture Productivity is an R&D partnership between Blue Hill Hydraulics Incorporated and Great Eastern Mussel Farms. The partnership performs hydrodynamic studies of aquaculture lease sites, assists with site selection and permitting, performs productive capacity studies, and provides consultation on the topics of aquaculture technology and husbandry practices.

Aquaculture Productivity's principal investigators are Carter Newell and John Richardson. Carter Newell has 25 years of aquaculture experience working for Great Eastern Mussel Farms and being one of the founding members of Pemaquid Oyster Company. John Richardson has 15 years of aquaculture experience developing hydrodynamic models of lease sites and performing productive capacity studies. The partnership is equipped to perform field studies with the latest generation of field data collection equipment and maintains a state-of-the-art computing laboratory.

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