Installing Blocks of Fish Reefs in the Deep Sea
Type:
Presented during:
WODCON XX: "The Art of Dredging" - 2013, Brussels, Belgium
Authors:
Yamamoto K
Abstract: With their abundance of marine resources, the bodies of water off the coast of Japan have long been home to a thriving fishing industry. However, in recent years, the ever-increasing catch made possible by improving fishing techniques and unrestrained exploitation has inevitably affected these resources. Yields from offshore fishing have dramatically declined.
The government-run Fishing Ground Improvement Project, an initiative instigated by the Fisheries Agency to counter this trend, seeks to ensure steady yields by protecting and cultivating marine resources. Efforts currently underway as part of the Project include organizing fishing reefs to protect and cultivate snow crabs and flathead flounders within the exclusive economic zone in the western reaches of the Sea of Japan.
As part of the Project, we sought to establish blocks of artificial fishing reefs within a designated area, installed at equal intervals, to protect targeted marine life within the area from Trawlers. This area is located 30 to 50 km off the coast, far from land and in abysmal depths reaching 200 to 300 m. Making the Project still more arduous are the strong currents characteristic of the area. What was required was to install these reefs under unfavorable conditions while achieving a positioning accuracy of ±30 m.
To complete the various installation tasks under unfavorable conditions within the assigned work period, we needed to identify the days that would allow the execution of specific tasks and to carry out those tasks on the days assigned.
The actual installation work entailed a fleet of tugboats (350-ton suspension full-swing crane barges, among others), support tugboats, and anchor-handling boats.
In placing the blocks, we used a block-detecting/guiding system to ensure placement within requirements. We used an automatic separation mechanism to ensure the accuracy of block placement and safe, reliable separation of the individual blocks
The foregoing approach to these tasks resulted in successful placement of blocks of artificial fishing reefs with an accuracy of ±30 m in the ocean depths and allowed the completion of the installation within the predetermined work period.
The presentation here provides an overview of how this work was done and discusses various aspects of the work that led to successful completion.
Keywords: Deep water, Artificial fishing reef blocks, Block-detecting/guiding system,