...Change the Net Offshore

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Crew Discussion

Aquaculture operating in fully exposed, hostile offshore environments requires innovative problem solving to consistently raise fish. Offshore aquaculture sites have no protection from the natural elements and may regularly experience poor sea-state conditions which could be amplified when deploying offshore aquaculture components using a large boat and boat crane. Injuries to workers and damage to equipment and aquaculture components are legitimate concerns. The OAC has recently deployed a new net to their offshore Ocean Spar Sea Station cage. The crew and technicians met (Photo 1) to discuss plans for a new attachment procedure-from the bottom-up, as opposed to the previous top-down deployment method. A bottom-up strategy takes advantage of the more favorable work conditions at depth and neutral buoyancy of the spectra net.

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Bundled Net	Over the Side	Pulled to Ballast

Critical to this deployment method is that the net must be properly bundled to secure all loose ends and ensure twisting does not occur once the net is placed in the strong offshore currents (Photo 2). The net is placed in the water oriented such that the top of the net leads to the ballast weight (Photo 3). One rope is tied to the ballast weight, passed through the middle of the net, and tied to the boat to ensure divers can maintain control of the net in the strong current. A second rope is also tied to the boat, passed through a shackle on the ballast weight, and tied on the other end around the net. The latter rope is used to pull the neutrally buoyant net to the ballast weight while divers guide the descent (Photo 4). Once to the ballast weight, the ropes are untied and divers place the net over the ballast weight. Two new ropes were lowered down the length of the spar and tied around the netting. As the divers moved the net up the spar, two other individuals, standing on top of the spar, kept these ropes taut thereby maintaining the net's position as it moved up the spar.

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Begin Attachment	Spar Tow	Attaching Net	Final Shackles

Eventually, the net is moved up to the water surface and shackled to the top of the spar (Photo 5). The net is attached initially to the up-current side of the cage to take advantage of the strong current. The spar is then towed into the proper position allowing the other side of the net to be attached (Photo 6). Eventually the entire net is secured to the rim using 16 shackles (Photos 7 and 8). The cage is secured in this configuration for the night and the following day the harvest ring is secured to the bottom of the spar by traditional methods.