The Conceptual Offshore Aquafarm

Description of the demonstration project currently under development by UM-RSMAS and Snapperfarm, Inc.
 

The offshore areas of the Southeastern U.S. and the Caribbean countries have extraordinary potential for the development of an environmentally sustainable mariculture industry. Site selection is the first and most crucial step taken to ensure environmental sustainability and successful implementation of the Offshore Aquafarm. A detailed site assessment was conducted to evaluate parameters related to infrastructure, topography, bathymetry, meteorology, hydrology, environmental and biological information, as well as the legal, social, economical and political framework. Areas of potentially conflicting use were avoided. These criteria were carefully studied to ensure the technological, environmental, social, and economical feasibility of the operation.

The Offshore Aquafarm demonstration project is completely submerged, as illustrated in the accompanying figure. This preserves the aesthetic aspects of the area. In compliance with USCG regulations, systems comprised of cages, rafts, lanterns, longlines and moorings will clear at least 40 ft (12m) from the surface in order to avoid
impediments with navigation. The depth of the site (90-100 ft/30m) and steady current (0.5-1.5 knots) maintain water movement in a downstream direction, dispersing organic and inorganic pollution that could potentially be associated with aquaculture operations. No coral reefs are present in the area surrounding the Offshore Aquafarm. Rather, sparse patches of Halimeda - a macroalgae characteristic of oligotrophic environment- are found at the predominantly sandy bottom. The cages stocked with with hatchery-reared cobia and snapper for growout, inevitably generate a certain amount of nutrients and suspended solids, which is not dramatically affecting the nutrient deprived, offshore environment due to its carrying (i.e., environmental) capacity. Downstream from the cage site, the concept includes the deployment of rafts and longlines of filter feeder mollusks and banks of macroalgae that will utilize the inorganic nutrients being released by the system.

The submergible cages also function as FADs (Fish Aggregating Devices). Since an estimated 50% of the hatchery-reared fish will be suitable for stock enhancement
purposes, FADs will provide the ideal habitat for releasing fish. Additionally, the combination of FADs and hatchery-reared released fish will promote the enhancement of fish stocks in the area. The concept of Acoustic Ranching in Aquaculture (ARIA) will also be tested.

To ensure long run autonomy of the Offshore Aquafarm, a state of the art marine hatchery and school will be established in the Island of Vieques and/or Culebra. The marine hatchery and school are seen in the background of the accompanying illustration. An educational program and curricula will be established for training of personnel at all levels, from high-school to technical and graduate level. Simultaneously, the marine hatchery will be producing larvae, post-larvae and juveniles of high-value marine fish and invertebrate species for aquaculture and stock enhancement.

The submersible cages, called SeaStation, are state of the art, manufactured in the U.S. by Ocean Spar Technologies, one of our private sector technological partners in the project. To ensure long term sustainability and develop this concept properly, scientific research is required. For example, environmental models based on energy budgets, mass balance, current velocity and direction, depth (bathymetry) and water quality parameters must be constructed to determine the amount of solids and nutrients being generated by the fish cages to estimate the biomass of filter-feeder mollusks (oysters, mussels) and nutrient-stripper macroalgae (Gracilaria, Ulva) required to clean up the water downstream. These parameters can be determined using mass balance and differential equations. The environmental or carrying capacity of the area must be precisely determined to avoid the risks of eutrophication. Since the cages deployed and their mooring systems will act as artificial reefs or FADs (Fish Aggregating Devices), the model should also incorporate data on fish and invertebrate assemblages surrounding the cages.

The Offshore Aquafarm will be autonomous and self-sustained. Automated feed hoppers loaded with environmentally friendly feeds will dispense automatically pre-calculated rations to ensure the highest assimilation and feed conversion rates with minimal organic and inorganic wastes. A key determinant in the success of major aquaculture operations is the ability to monitor water quality parameters such as temperature, salinity, oxygen, pH, suspended solids, as well as nutrients, in order to determine whether fish feeds are being dispensed at the optimum rate. We propose to accomplish this by installing autonomous monitoring devices with several sensors in the cage system. The Seakeepers monitoring device will allow for gathering and transmission of real time data via satellite to computerized systems in the control room at the hatchery. This will be a fundamental tool in assisting the development of improved management strategies for minimizing solid organic and inorganic wastes (feeds, feces and nutrients) as well as promoting optimal food conversion and growth rates. The International SeaKeepers Society, which owns a patent on this monitoring device, is a technological partner in the proposed offshore project.

Properly developed, this concept may enable the simultaneous development of aquaculture of high-value organisms that feed low in the food chain such as filter feeders and nutrient strippers in areas of the Caribbean which could otherwise not be utilized for any purpose because of the extremely low productivity. Mollusks and algae, for instance, can only be cultured in nutrient rich areas. Therefore, nutrients and solids being released by the fish cages will create a favorable environment for raising species of mollusks and algae that could, in turn, provide additional crops while removing the organic and inorganic nutrients from the area. The Center for Sustainable Fisheries is supporting this initiative.