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Feature Article

Developing a Remotely Operated Submersible Fish Cage System
New Cage Design Could Help Protect Fish Stock From HABs and Other Shallow-Water Hazards

Dr. Tae Ho Kim
Associate Professor
School of Marine Technology

Dr. Seung Sik Shin
Associate Professor
Division of Business and Commerce
Chonnam National University
Yeosu, Korea

Kyu Serk Hwang
Technical Director
Sungsin Shipyard Co. Ltd.
Ulsan, Korea
Korean coastal waters have experienced a significant increase in the frequency, severity and duration of harmful algal bloom (HAB) events, which can cause large economic losses in the aquaculture and fishery industries and have major environmental and human health impacts. HABs associated with the planktonic dinoflagellate, Cochlodinium polykrikoides, have been known to be responsible for massive fish kills during the summer and fall seasons in Korean coastal waters. These 'red tides' occur in the surface waters to an approximate depth of 3 meters and affect the economies of local coastal communities by causing fish mortalities.

In the aquaculture industry, having the ability to submerge a farm of fish cages below this level during one of these HAB events could help protect the fish from harm. A submersible fish cage could also avoid other substantial operational challenges that exist in surface-based fish farming, including heavy storms, jellyfish infestation, unsuitable temperatures, high pollutant levels, oil spills and many types of biofouling.

A worker checks the control station on top of the remotely operated submersible fish cage system.

Submersible Fish Cage Development
The primary objective of designing this submersible fish cage system was to provide the capability of reducing the mortality of farmed fish due to HAB toxicity in coastal waters.

The cage consists of 12 angled, rigid-frame components with both a containment and cover net, 12 upper floats, 12 tanks (for fixed and variable ballast), mooring ropes, anchors, a control station and a surface control panel. The upper frame has 12 fixed flotation tanks, and the lower frame has six fixed flotation tanks and six variable ballast tanks. The fixed ballast tanks allow workers to adjust buoyancy manually, while a control system can remotely adjust the buoyancy of the variable ballast tanks.

Control System. The mechanical components of the control system are attached to the top of the fish cage and tethered to the surface control panel. This allows the operators at the surface to regulate either the flow of air or seawater in the variable ballast tanks. The surface control panel regulates a compressed air source with six two-way and 12 three-way valves. It also has three clinometers, four electrical terminals and the necessary air hose connections.

The control station is designed to be watertight and is attached to the center of the upper frame of the cage with stainless steel turnbuckles and wire rope. It was also connected via electrical cables to the surface control panel located on a service vessel. Operation buttons and LED lamps on the surface control panel indicate the normal, descent and ascent modes of the cage operation and to show the status of motor valves. In addition, the surface control panel incorporated digital indicators that display submerged depth and inclination of cage during descent and ascent.

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Dr. Tae Ho Kim is an associate professor at the School of Marine Technology of Chonnam National University in Korea. He received a Ph.D. in ocean engineering from Pukyong National University. His research interests involve design and development of fishery systems and facilities.

Dr. Seung Sik Shin is an associate professor at the Division of Business and Commerce at Chonnam National University in Korea. He received a Ph.D. in economics from Korea University. His studies have focused on the economic aspects of marine systems, especially for fisheries.

Kyu Serk Hwang is a technical director at Sungsin Shipyard Co. Ltd. in Korea. He received a bachelor's degree in mechanical engineering from Pukyong National University in Korea. His interests are developing marine systems, especially for offshore fish cages.

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