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www.sea-technology.com June 2016 / st 33 T he Pacifc abalone, Haliotis discus hannai, is a very valuable species that is commercially avail- able in South Korea. The production of the abalone at a commercial scale began in South Korea in the 2000s, and the country is currently the second big- gest producer of cultured abalone in the world, with 8,977 tons produced in 2014. The abalone production system in South Korea is divided into two stages: seed production and rearing. Abalone seeds are produced at about 500 hatcher- ies, and almost all juveniles are reared using approxi- mately 500,000 sea cages. Abalone is cultured in the south, specifcally in the coastal waters of the Jeonnam province, where it is the most common species. However, Korean coastal waters have been polluted by many anthropogenic sources that affect the dissolved oxygen (DO) levels. The DO levels within a nearshore abalone farm could be as low as 40 percent saturation (4.0 mg/L), and the low DO levels limit the production of many aqua- culture species because DO limits growth by limit- ing the scope of the aerobic metabolism. As the intensity of farming increases, the DO level and its impact on abalone growth will become more important for farmers. The spe- cifc growth rate (SGR) is signifcantly affected by hypoxia. Therefore, in order to expand abalone aquaculture op- erations, using more exposed, often underutilized sites with better DO exchange is an option. However, these sites can be subject to high-energy conditions, including strong oce- anic currents and irregular seas, especially those related to typhoon events. Moving the existing structures to more ex- posed sites is not recommended because most of the existing abalone cage systems utilize net cages that are mounted on raft-type structures that maintain their buoyancy with Styro- foam billets mounted under square frames made of polyeth- ylene pipe. These cage systems are fragile, and most were destroyed in 2011 and 2012 by typhoons with high waves and strong currents. Thus, the primary objective in designing the submersible abalone cage system described in this study was to provide the capability to reduce system damage while operating with compressed air in the open sea. Submersible Abalone Cage Design The submersible abalone cage grow-out system is de- signed as a modular box with a commercial size. An inline combination of currents with a magnitude of 1.0 m/s, ir- regular waves with a signifcant wave height of 8.01 m, and a peak period of 12.52 s was considered. The submersible abalone cage system we designed is free to move vertically within the water column by adjusting the weight and buoy- ancy. To control the surfacing operations, compressed air is introduced into variable ballast tanks to displace water. When descending, air is discharged from the tanks, allow- ing seawater in, thus increasing the weight of the cage sys- tem, causing it to sink. The submersible abalone cage system is comprised of rigid frame components with 25 fxed ballast tanks, 24 vari- able ballast tanks, a walkway, 16 containers and 192 shel- ters for abalone, a balance control valve, an air compressor, a manifold, a valve to regulate the fow rate of the com- pressed air, air hoses to transfer the compressed air, moor- ing ropes and anchors, and ropes that regulate the targeted sinking depth. The cylindrical tanks used for the fxed (508 mm in diameter and 2,900 mm in length) and variable bal- last (700 mm in diameter and 1,200 mm in length) were made from steel pipe coated with zinc. The tanks were in- stalled on the bottom of the square shape, so the abalone cage system would submerge evenly. Buoyancy increases when the air generated by the compressor is injected into Submersible Cage System for Abalone Aquaculture Design for Open Sea Can Avoid Extreme Wind, Waves By Dr. Taeho Kim • Dr. Moo-Hwan Oh The abalone cage system consists of a combination of four-by- three containment module confgurations mounted within a frame.