...Deploy an Offshore Aquaculture Cage

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Ocean Spar Sea Station	Rim Assembly	Towing Operation

The Gulf of Mexico Offshore Aquaculture Consortium utilizes a 600 m³ Ocean Spar Sea Station cage that measures approximately 16 m wide and 11 m high. The cage retains its shape and volume through its semi-rigid structure and netting and without assistance from traditional gravity and tensioned anchors. In its final configuration, the cage has a double-cone shape that is considered ideal for raising a pelagic fish species, providing increased internal volume (Illustration 1). The cage components were shipped to the National Marine Fisheries Service lab in Pascagoula, MS. This facility provided sufficient workspace to assemble the 15-m octagonal rim (Photo 2), and stage the various cage and mooring components near the water. The octagonal rim is composed of eight flanged sections of steel pipe that are individually pressurized and sealed to allow floatation on the water surface. The assembled octagonal rim was hoisted to the water surface and towed to the distant offshore aquaculture site with the central spar buoy inside the rim, in a horizontal position on the surface during the towing operation (Photo 3).

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Mooring Connection	Ballast Placement	Spar Rotation

Upon arriving at the site, the octagonal rim was connected to the single-point mooring using two bridles connected to two flange intersections of the rim (Photo 4). The ballast weight, a circular concrete block weighing approximately 3,200 kg, was lowered to the water surface, and attached to the bottom of the spar that was floating on its side nearby. The boat crane slowly lowered the ballast weight deeper in the water until it rotated the spar into a vertical position (Photos 5 and 6). The spar has a variable buoyancy chamber that controls the depth of the cage-to lower the cage a valve is opened on the top of the spar allowing air to escape and water to enter into the bottom of the spar. To raise the cage air from a SCUBA tank is introduced into the top valve of the spar displacing the ballast water in the bottom of the spar.

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Harvest Ring Assembly	Net Placement	Net Assembly

The harvest ring is next lowered over the top of the vertical spar (Photo 7). The net was lowered over and attached to the top of the spar (Photo 8), followed by the work platform, positioned on the top of the spar and bolted in place. The spar was then floated to the center of the octagonal rim. The netting was stretched to each flanged region of the octagonal rim and shackled to the inside corner of the rim section (Photo 9). This completed formation of the upper-cone section of the cage and created a very taut net. The lower portion of the net was attached to the harvest ring which was then tightened down to the bottom of the spar using long threaded rods.

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Finished by Sunset