development during recent decades has been made possible by the carefully coordinated, nationwide cooperation between the government, fishing cooperatives (to which virtually all fishermen belong) and scientists at regional, prefectural, and university laboratories and equipment stations.. The national government currently provides about 60 percent of the funding for larger projects, with the remainder coming from prefectural and municipal governments and local fishing cooperatives.

Since 1952, fisheries development has been carried out through a series of long-term national programs. By coordinating a number of diversified projects, these programs have altered the nature of coastal fisheries and have contributed to appreciably increasing the income of coastal fisher

men.

Improvement of grounds and resources received emphasis during the 1950s in projects designed to improve coastal habitat by removing unsuitable reefs and creating new shelter areas; to improve cultivation grounds for scallops and other shellfish; to provide facilities for the collection of seaweed (nori) spores; and to develop the expertise needed to stock and transplant juveniles of valuable species of fish and shellfish.

From 1962-1975, projects emphasized coastal aquacultural development and involved the construction of artificial mass culture facilities for shellfish and seaweed, aquacultural pens for open water fish culture, wave-damping breakwaters, and waterways to improve water exchange in inner bays. Improvements continued to be made in shelter design, and the use of specially designed concrete blocks was expanded-more than a million were placed at over 3800 locations by 1970. Aquacultural grounds were dredged, cultivated, and fertilized, while predator and disease control were improved. Technical developments in seedling production and stocking of scallops, abalone, yellowtail, shrimp, salmon, and seaweeds established Japan as the world leader in marine culture.

えび肉

Present Program

The present seven-year Coastal Fishing Grounds Adjustment and Development Project, which began in 1976, is the result of a 1974 law in which the national government allocated over a billion dollars to enhance coastal fisheries. The project emphasizes habitat improvement as a way to enable Japan to meet its seafood requirements in an era of 200-mile limits and increasing fuel costs.

The thrust of the new project results from a careful reevaluation by Japanese scientists and economists of the viability and economic feasibility of some of the massive stocking projects undertaken during the past 15 years. While the technological advances of the 1960s and early 1970s made possible the mass production of juveniles of a number of species, the survival of the juveniles after stocking, and economic return generated by these programs, came under scrutiny. The fate of juveniles after stocking was considered to be a weak link in the production system, and the new program was designed to integrate some of the hatchery and habitat improvement projects and maximize the productive potential of the coastal zone. This new project expands the earlier intensive" aquacultural activities in ponds, pens, or from rafts, to what is now commonly called "culture-based fisheries."

Concrete jacks used to

stabilize gravel at Tokushima.

近海魚

"Tsukiiso" abalone shelters, FRP with stones, manufactured by Asahi Chemical International Ltd. (Photo courtesy of Dr. Ogawa)

Fishing Ground Construction-
Artificial Reefs

Japanese fish shelters are commercially manufactured from reinforced concrete, steel, iron, or petroleum-based materials such FRP and PVC, according to designs resulting from extensive engineering efforts undertaken by corporations, national laboratories and universities, and from the biological research conducted by the regional prefectural laboratories in conjunction with fishermen. A variety of large scale shelter units which have undergone extensive testing are now being mass produced and placed along the coasts of Japan. These include bottom reefs and moored mid-water and surface structures.

The buoyant fish attractors, both surface and mid-water, are designed to attract pelagic species. They are used to concentrate fish, alter normal migratory routes, and attract fish to specific water layers to avoid pollutants. Some of the shelters are used in conjunction with feeding programs to increase their effectiveness. Generally the mid-water and surface structures are moored in water between 60 to 100 meters deep and some surface units are capable of being placed in water up to 200 meters deep.

Artificial reefs, termed "gyosho" in Japan, are placed either to expand existing natural reef areas or to create new commercial fishing grounds in areas which were previously sparse or marginally productive. Projects to expand existing grounds require a minimum site area of 2500 square meters,

T

he Agricultural Civil Engineering Laboratory in Kanagawa Prefecture has been conducting studies on the hydraulic factors involved in reef placement and site selection. This research has provided some new ideas on how reefs function. When currents impinge on reefs, instabilities occur between vertically stratified fluid layers which generate internal waves. Studies demonstrated that the presence of internal waves significantly influences pelagic fish distributions. Acoustical observations indicate that fish concentrations correlate with the presence of lee waves resulting from the interaction of currents with the reefs. Results of these studies suggest that the aspect ratio (height of the reef to water depth) should be between 1/20 to 1/5, depending on local conditions. Other studies concerned with benthic fish indicate that the width of the reef is an important factor in fish abundance.

Research at Hokkaido University's Fisheries School has contributed to the development of new techniques for placing reefs which reduce damage and permit controlled spacing of shelters. Spacing has been shown to influence turbulence effects. The influence of reef shapes has also been examined in efforts to design reef units that attract the more important commercial species.

Most of the larger reefs ("jumbo gyosho') are designed to promote an upward current deflection, provide sheltered, darkened, calm areas, and allow for adequate circulation within the units. Many of the shelters are built from prefabricated components which are assembled at the shore staging area and transported by barges to the site. Some can be built in a variety of configurations from basic unit components. Fiberglass reinforced-plastic units are manufactured by Asahi Chemical International Ltd. in a variety of shapes and

sizes. Twenty-three of these reefs have been constructed using units which range from 41 to 720 cubic meters each. These units have a large surface area which is rapidly colonized since there is no alkaline leaching. The reefs are generally weighted with concrete according to the site bottom type, wave conditions, and current velocity. The weight per unit area of these units is less than half that of concrete and they can be used in areas unsuitable for the more massive units. Installation is somewhat less expensive since the units can be towed to the installation site with the aid of air bag floats.

"Dragon Reefs produced by the Onoda Cement Co. Ltd. have been placed at eight sites. The number of units per site ranges from 3 to 30; each unit weighs about 34mt and has a volume of 131 cubic meters. These units are made from eight reinforced concrete panels which are bolted and mortared together, and placed by a floating crane and barge. These shelters produce good current deflection in all orientations and influence both benthic and pelagic species. During the current year 150 additional units will be installed.

Reef units produced by Ishikawajima-Harima Heavy Industries Co. have been placed at 32 sites. Each site holds between 10 and 50 units, and each unit weighs about 22mt and has a volume of 139 cubic meters. These units are designed to generate an upward current which produces conditions conducive to fish congregation. The structure is built from reinforced concrete panels which are coupled together into triangular columns. They are installed using a floating crane.

Improvement Programs for
Specific Species

Most of the reefs designed for specific species are for invertebrates or seaweeds. Such small, shallow water reefs are known as 'tsukiiso" in Japan. Over 40 percent of the current large-scale projects using this type of reef are for abalone, a very valuable species subjected to heavy fishing pressure.

A number of abalone hatcheries in Japan produce over a million juveniles (1.5 to 3.5cm) each year. Some of these hatcheries use warm water from electric power plants or geothermal sources to increase their production. The juveniles are generally sold to the fishermen who stock them in their fishing grounds.

Since hatchery-reared abalone can be distinguished from natural abalone by a shell color variation, fishermen and researchers can evaluate the effectiveness of the stocking programs. Return has been quite variable, ranging from almost zero to as high as 70 percent. One of the reasons postulated to account for this variation is the differences in the stocking habitats. Research indicates that stocking conditions in some areas could be greatly improved by altering the natural bottom with special shelter units.

A variety of special units are now being tested or are in use. Some are designed especially for juveniles; others for adults. Still other units are designed to improve conditions in natural nursery areas by limiting wave action, promoting food seaweed growth, or stabilizing the bottom. In some cases, special shelter units, designed to minimize predation or food competition, are directly stocked with juveniles.

Tokushima Nursery Ground

Ecological studies in areas subjected to heavy storm wave conditions indicated that the wave action on inshore gravel and cobble is responsible for significant mortality in juvenile abalone in a natural nursery ground. The wave action also reduces the attached seaweed which provides the primary food for the growing abalone.

An effort to create an artificial nursery area has been undertaken by the Tokushima Prefectural Fisheries Experiment Station in cooperation with the local fishermen's association. It is funded, in part, by the national government. The project is designed to reduce wave action, promote seaweed growth, and stabilize near-shore gravel beds which are the habitat of newly settled abalone.

Based on biological, physical, and geological studies, a site near Abu City was chosen. Three types of concrete units were used to construct the nursery ground. At the seaward edge of the nursery, large hemispherical blocks weighing about 15mt where placed in two rows (1-2m deep) to break waves. Inside this area, truncated pyramid-shaped blocks with attached lines were placed to aid seaweed growth. In the near-shore (0.5m) zone, small jack units, with grooves to provide additional shelter for the juveniles, were set in the coarse gravel to stabilize the bottom.

Preliminary estimates are that survival and growth of naturally spawned abalone have been increased in the nursery area. Studies on predation rates and general ecology are now in progress.

Fukushima-Taise Stocking Ground

In waters surrounding Hokkaido, the northernmost of Japan's major islands, several projects are aimed at integrating hatchery production with habitat improvement. These projects, conducted under the guidance of the Hokkaido Institute of Mariculture, are designed to increase the survival and growth of hatchery-stocked abalone by placing them in specially prepared shelter units.