Shift from the Clean Sea to the Bountiful Sea
Osaka Bay Fish Farm
Concept: Obayashi Project Team

(3) Coastal Farm
The coastal farm consists of onshore facilities, the eutrophic ponds that are built on the shore, and reef seaweed beds. The nutrient cycling method and the way the seaweed beds are used is similar to that of the other farms, but the coastal farm has its own unique and important role to play.
The onshore facility will also grow fish, raise fish fry and mollusks, and cultivate the food for fish and shellfish to preserve the fish species which need the protection in Osaka Bay and maintain the health of the bay. Recent increases in seawater temperature have destabilized the growth of fish fry. It is expected to will become increasingly important to hatchlings and fry to maintain the stability of native species. Sunlight will be used on the rooftop of the facility to cultivate microalgae (phytoplankton) used to feed the fry and juvenile fish. In addition to the aquaculture facility, there will also be a research facility and an integrated smart fisheries-related management facility.
An important part of the coastal ranch is its role as a place to teach people about fish-eating culture, raise awareness, and provide hands-on experience.
In the indoor seminar room, "Fish-eating culture seminars" will be held to trace the history of fish eating and to share accumulated wisdom and knowledge. Research presentation on fish nutrients will also be given. The facility's kitchen will hold cooking classes demonstrating the preparation of the Osaka Bay "pride fish" yellowtail grouper as well as other under-used species. There will be nutrition education "fish events" for children and cooking workshops where participants can learn how to cut and prepare fish. Visitors will be able to learn about the role of seaweed beds and about the creatures of the sea through viewing tanks and by touching pool.
The facility will be more than just a learning center; it will also offer visitors a number of entertainment options. There will be a restaurant featuring traditional seafood cuisine, a barbecue terrace where visitors can enjoy beach grills and fisherman's hot pots. The seaside area will be a place to enjoy fishing and diving, available to the public. An underwater tunnel facing the sea will allow visitors to observe seaweed beds and the fish that live among them.

[Coastal Fish Farm Floor Plan (1 unit)]

[Coastal Fish Farm C-C' cross sectional view]

[Image of underwater tunnel]

Validating the Balance Between Aquaculture and Seaweed Beds and Facility Size
What kinds of fish catches can this project actually yield?
Data on seafood consumption in Japan is published by the Ministry of Internal Affairs and Communications. Since the most detailed data available focuses on red sea bream, we have used this fish to model the productivity of the fish farm concept.
Each year, the people of Osaka Prefecture consume a total of 3,438 tons of red sea bream. Wild-caught red sea bream from the waters off Osaka Prefecture makes up 3.34% of that quantity.
The aquaculture ponds in the bay can accommodate five adult red sea bream weighing approximately 2 kg per square meter, so the final production capacity of a single unit would be 18 tons per year, with ten units producing 180 tons per year, which represents 5% of Osaka Prefecture's total consumption.
The annual production capacity of a single unit of the out-bay fish ponds is 12 tons. Thus, 10 units would produce 120 tons per year, or 3% of Osaka Prefecture's total consumption.
In other words, the Fish Farm project can provide as much as 8% Osaka Prefecture's red sea bream consumption.
Moreover, the data on the absorption of nutrients, also based on red sea bream data, shows that an area 20 to 40 times larger than the project plan would be required to absorb all of the nitrogen and phosphorus discharged by aquaculture using the seaweed beds. But since red sea bream swims and feeds relatively well among the fish species which are slated for production in the project, it is safe to assume that the amount of feeding, nitrogen, and other discharges will be less than for other fish species. In this project, the nitrogen, phosphorus, etc., which are biologically treated by the water treatment system, are first released as nutrients into the eutrophic ponds adjacent to the aquaculture ponds. Phytoplankton and bivalves such as clams and red clams absorb these nutrients. Since bivalve nutrient uptake is extremely fast, most of the nitrogen and phosphorus would be absorbed by bivalves, with the remaining nutrients supplied to the seaweed beds. In addition, water quality will be monitored at the margins of the seaweed beds. Should nitrogen levels in excess of the effluent standard be detected, the pumps will be turned off to control the discharge of water and reduce the outflow of nutrients from the aquaculture ponds and eutrophic ponds. Based on these calculations, we assumed that good water quality in the project will be maintained in the system which combines the seaweed beds and nutrient cycling.
Utilization of Offshore Wind Power Generation Facilities
One approach to anchoring the fish farm facilities might be to use piles that are driven deep into the seabed, the method that is currently in use around Japan for offshore wind firm. For example, if wind turbines are positioned at intervals of 1 km, the same units as on the in-bay farm facilities would be arranged as shown in the figure above. The units would be connected and the four corners of the entire structure would each be anchored to the base of windmill pillars. It would be easy to make up for a lack of strength of the mooring rope or the of the unit connectors by anchoring the mooring at an intermediate point on the seabed.
The efficient and economical approach might be to use what is readily available: wind turbine columns. This method is likely to be feasible since it is already well known that existing fishing and shipping industries can continue to function without disruption during the construction of offshore wind power generation facilities.

IV. Afterwords
For centuries, the Japanese people have reveled in the changing seasons and the wide assortment of fishes available with each passing season. That's why it would simply be wrong to try to force-fit an approach to aquaculture, similar to that in the Europe and North American, in which a single variety of fish is produced in massive quantities (monoculture). We were surprised to learn that there are already many fish farming methods being considered in Japan, including some that are still in the research stage of development. In the process of studying the project, the team found that while the effects of global warming may be depleting coastal fishery resources and the need to nurture fisheries is increasing, there are in fact ways to restore to bountiful sea and to nurture a fishing industry that makes the most of Japan's unique characteristics.
The spotlight is increasingly turning to the effectiveness of seaweed beds in absorbing and fixing carbon dioxide. In that context, the Fish Farm, which puts seaweed beds front and center in the concept, serves as an example of a fishing industry that is uniquely Japanese. Further, by combining seaweed beds with aquaculture, we believe that this is a method that can support appropriate maintenance and management of seaweed beds and their effective use as an economically rewarding seaweed bed fishing ground.
We know that it will be important to collaborate with fishermen and other stakeholders, as well as to give due consideration to navigation routes to ensure the economic viability of the project. However, I would be happy to see the development of "nurture fisheries" that are right for each region and adoption of technologies and concepts that take advantage of nutrient cycles and nature's innate ability to regulate life cycles and habitats in as many places as possible.
We hope that this project will serve as a catalyst for many people to think about the diversity of marine life and the marine environment, and to consider what a sustainable fishery and aquaculture industry should look like. We sincerely hope to see the creation of a "bountiful sea" where seaweed and seaweeds thrive and a variety of marine organisms can live.
Finally, in developing the concepts underlying this project, the members of the Obayashi Project Team would like to express their profound gratitude to the many individuals who graciously shared their invaluable time and expertise in support of this project, among them Professor Emeritus YAMOCHI Susumu of Osaka City University, Professor ISHIGAKI Mamoru of the Hiroshima Institute of Technology, Mr. HORI Masakazu, Advisor of the Japan Blue Economy Association, Professor KITAZAWA Daisuke of The University of Tokyo, Dr. HOSOKAWA Takashi of Nitto Seimo Co., Ltd.
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The issue this article appears

No.63 "Fishery"
Our country is surrounded by the sea. The surrounding area is one of the world's best fishing grounds for a variety of fish and shellfish, and has also cultivated rich food culture. In recent years, however, Japan's fisheries industry has been facing a crisis due to climate change and other factors that have led to a decline in the amount of fish caught in adjacent waters, as well as the diversification of people's dietary habits.
In this issue, we examine the present and future of the fisheries industry with the hope of passing on Japan's unique marine bounty to the next generation. The Obayashi Project envisioned a sustainable fishing ground with low environmental impact, named "Osaka Bay Fish Farm".
(Published in 2024)
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Drawn Fishery and Fish
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A History of Japan’s Seafood Culture: Focusing on Fermented Fish
SATO Yo-ichiro (Director General, Museum of Natural and Environmental History, Shizuoka; and Emeritus Professor, Research Institute for Humanity and Nature)
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The Future of Our Oceans, Marine Life, and Fisheries: Biodiversity and Environmental Conservation
MATSUDA Hiroyuki (Emeritus Professor and Specially Appointed Professor, Yokohama National University)
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What Will Be on the Table in 10 Years?: The Challenge of Fisheries GX
WADA Masaaki (Professor, Future University Hakodate and Director, Marine IT Lab, Future University Hakodate)
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Fishery This and That
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OBAYASHI PROJECT
Osaka Bay Fish Farm - Shift from the Clean Sea to the Bountiful Sea
Concept: Obayashi Project Team
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FUJIMORI Terunobu’s “Origins of Architecture” Series No. 14: Seagrass Houses
FUJIMORI Terunobu
(Architectural historian and architect; Director, Tokyo Metropolitan Edo-Tokyo Museum; and Emeritus Professor, University of Tokyo) - View Detail
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Fish Culture This and That
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