INTRODUCTION
Japan has long been recognized as a leader in the aquaculture of molluscs. In 1969, approximately 560,000 tons (with shell) of shellfish were harvested (Japanese Fisheries Association, 1971). Principal species under cultivation include Pacific oysters, Crassostrea gigas, scallops, Patinopecten yessoensis, and the abalone, Haliotis discus. Several species of clams and snails also play an important role in the total production figures, but these are mostly caught from wild populations and are not farmed to any extent.
During my short tour of aquaculture sites in Japan related to the UJNR (United States-Japan Natural Resources) Aquaculture Panel, I concentrated my effort on surveying the areas where oysters, abalone, and scallops are being farmed. An overview based on these visits is listed below.
Oyster production in Japan has shown a steady increase in recent years. From 1958 to 1968, landings rose from 151,894 tons (with shells) to 265,881 tons (Furukawa, 1971). Production declined slightly in 1969 when 245,000 tons were harvested (Japanese Fisheries Association, 1971).
A major reason for the increase in production is the expansion of the hanging method of oyster culture, raft, longline, and rack. By using the third dimension, the yield per acre is greatly increased over the bottom or sowing method. Furukawa (1971) estimates that the oyster yield from raft culture in the Hiroshima Prefecture is 20 tons of oyster meats per acre per year. These figures compare favorably with Ryther and Bardach's (1968) estimate of 23.3 tons per acre per year.
The entire industry is dependent on the natural production of seed oysters. Both scallop shells (northern and southern variety) and oyster shells are used for cultch. Shells are strung on wires (1/2-inch bamboo spacers are used to separate scallop shells) and draped over racks. Following setting, the seed caught on scallop shells is used domestically while a considerable portion on oyster shells is exported to the United States and France.
Two major areas of oyster production were visited during the tour--Miyagi and Hiroshima Prefectures. In addition, we visited Lake Hamana, the only saltwater lake in Japan, where shallowwater rack culture is being carried out.
According to Furukawa (1971), Miyagi Prefecture produced 3,814 tons of oyster meats in 1968, or about 9.3% of the total Japanese production. Matsushima Bay has been one of the most important culture areas in Miyagi Prefecture. In 1959, 1,456 tons of shelled oysters were harvested. However, beginning in 1961 mass mortalities occurred in Matsushima Bay. Total annual losses from 1961 to 1964 were 62.5, 41.6, 42.3, and 51.9%, respectively (Ken-no et al., 1965).
From our on-site visit of Matsushima Bay, it was apparent that the Japanese had solved their oyster mortality problems by converting the Bay's use from oyster culture to seaweed culture. Very little oyster culture in the Bay proper was observed.
Yet, total oyster production for Miyagi Prefecture has declined only slightly. The Japanese have expanded raft and longline culture in areas outside Matsushima Bay.
One big industry in the Miyagi Prefecture is the exportation of seed oysters. On our tour, we had the opportunity to visit this operation at Watanoha as they were preparing seed for air shipment to France. Oyster seed, which is hardened on racks for 3 mo, is brought ashore in small boats. The seed (all caught on oyster shells) is removed from the galvanized wire strings, placed in baskets, and thoroughly washed. It is then culled into single pieces and examined for predators; all shells with six or less spat are discarded. The good shells are placed in freshwater for 1 hr to kill flatworms, Pseudostylochus sp. After a quick saltwater dip (5 to 10 sec), 750 spat-laden shells are placed in shipping cases. Before wrapping, a random sample of 50 shells are taken out of the case and the number of seeds counted. Within 48 hr after crating, the seeds reach France.
The French's interest in Japanese seed has come about only in recent years. Heavy mortalities have occurred among the Portuguese oyster. Crnssostrea angulata, in France, and the government has banned the importation of Portuguese oyster seed in their country. In its place, they are now importing seed from Japan.
The new competition for Japanese seed could have two implications in the U.S. Pacific coast oyster industry: 1) the cost of Japanese seed to the United States could increase, and 2) because the French have entered the market, there could develop a possible shortage of Japanese seed for importation to the United States. In 1972, heavy sets of Pacific oysters occurred on the west coast, so the need for Japanese seed, at least in that year, was considerably less.
About 77% of the total oyster production in Japan comes from Hiroshima Prefecture (31,188 tons of meat out of a 1968 total of 40,928 tons). Furukawa (1971) states that a total of 10,962 rafts (9.1 x 18.2 m average size) are utilized in the Prefecture.
During our tour of the area, seed oysters were being strung on galvanized wire and suspended from bamboo rafts. Initially, 1,600 strings (wrens) are suspended. As the oysters grow, the number per raft is reduced to 800. On each string, about 15 m long, spat bearing scallop shells are separated by a 9-inch bamboo spacer.
Each raft is constructed out of bamboo logs. A typical raft, 20 x 9 m, is supported by 25 Styrofoam floats, each the size of a 50-gal oil drum. Fifteen Boats are located down the center of the raft while two series of five floats are located along the outer edge. An iron cable runs down the center of the raft and is the connecting link between each series of four or five rafts. The rafts are held in place by six (5 tons each) concrete anchors. A typical raft, including labor, costs about $350 and takes a crew of four 1 day to build.
As in Miyagi Prefecture, the entire industry is dependent on natural setting. No attempt is being made to supplement natural sets with hatchery-reared stocks. The seed is caught in the intertidal zone on scallop shells draped over racks.
Several problems are facing the oyster industry of Japan. Of considerable concern is the increased threat of both domestic and industrial pollution. Industries are located in areas adjacent to oyster growing and setting areas. Further expansion of such industries could seriously affect the oyster industry.
Because the bulk of oysters in Japan are grown off-bottom, a considerable amount of labor is involved. In recent years, there has developed a serious labor shortage in the oyster industry. Young people do not wish to follow their parents in this line of work. Thus, simplification of techniques and development of mechanization in the oyster industry is urgently needed (Fujiya, 1970).
Abalone production in Japan has increased from 4,600 metric tons in 1964 to 6,500 metric tons in 1970. One possible reason for this increase is the effect of a large seed planting program. According to Sanders (1971), there are 16 laboratories in Japan artificially producing 2 to 3 million seed abalone annually.
A typical laboratory is the Kanagawa Prefectural Fisheries Experimental Station located on the island of Joga Shima near the City of Miura. Their quota, which is set by the government, is to produce about 300,000 seed abalone annually.
At the Station, mature abalone are induced to spawn by first air-drying and then placing them in shallow, standing water tanks which are exposed to sunlight. Apparently as the sunlight heats the water, the abalone spawn.
The fertile eggs are transferred to setting tanks located inside an adjacent building. These tanks are covered with black plastic sheeting to eliminate light. The larvae, which require no supplementary feeding, set in about 1 week on special plastic plates. These plates have been previously exposed to running seawater in order to obtain a film of diatoms, the food of young abalone. Since the larvae swim near the surface, the water is slowly raised in the setting tanks so that the setting abalone are distributed as evenly as possible on the plates. Once setting is over, the plates are transferred to outdoor tanks where the abalone continue to feed on the diatom film until they reach 5 to 10 mm in size. They are then removed from the plates and placed on either tiles, oyster shells, stones, or cross-shaped plastic configurations. At this stage, they are fed macroscopic algae such as Ulva and Laminaria. When the abalone are approximately 2.5 cm in size (about 8 mo to 1 yr old), they are sold to the fishermen for 10 yen each. The growth rates in the area of the Kanagawa Station are as follows:
| Age in yr | Size in cm |
| 1 | 2.5 |
| 2 | 6.0 |
| 3 | 11.0 |
| 4 | 14.0 (market size) |
The hatchery-reared abalone acquire a green shell coloration which natural populations do not have. This green "tag" helps to evaluate the government's success in this seed planting program since the color persists throughout the abalone's life. It has been estimated, on preliminary results, that there is a 10% recovery on planted seed (Ryther, 1968).
In addition to the Prefecture laboratories which are producing seed abalone, there are Regional laboratories (equivalent to Federal laboratories in the United States) which are studying the biology of abalone. One such laboratory is the Tohoku Regional Fisheries Research Laboratory located in Shiogama, about 10 miles northeast of Sendai. Several studies on the growth of abalone are now underway. These include studies on the growth of juveniles using different varieties of diatoms and the growth of older forms on different varieties of seaweeds.
Shogo Kikuchi, biologists at the Tohoku Laboratory, is initiating a large-scale study where he will establish an artificial kelp bed in one of the Japanese bays. It is planned to plant the area with 10 million seed abalone.There are many areas in Japan where abalone set but do not grow or survive due to the lack of macroscopic algae. The development of artificial kelp beds may help to solve this problem. Kikuchi plans also to keep a close watch on invading predators and develop control methods if such invasion does take place.
The only commercial company producing seed abalone in Japan is the Oyster Research Institute. The Institute is located on Mohne Bay near the City of Kesenuma. Under the initial leadership of Takeo Imai, the Institute has become famous throughout the world for some of the basic studies in molluscan aquaculture. Since the untimely death of Takeo Imai in 1971, Hisashi Kan-no of the Tohoku Laboratory has been Acting Director.
The tank farm at the Institute has been described in a number of papers (Imai, 1967; Ryther, 1968; Costlow. 1969). At the time of my visit, 80% of the tanks (there are 180 in all) were devoted to abalone culture. The remainder contained oyster and scallop seeds.
At the Institute, abalone are spawned in early September and the larvae are caught on plastic plates (coated with Platymonas and Navicula) similar to those used at the Kanagawa Station. As the juveniles grow, they are removed from the plates, placed in plastic containers wrapped in netting, and resuspended from the floating tank farm. Twice a week the abalone are fed seaweed such as Ulva and Laminaria. When they are 20 mm or larger, the Institute sells them to the fishermen for 1 yen/mm.
The Institute has a cooperative program with the Sendai Thermal Power Station located near Shiogama on Matsushima Bay. Young abalone (1 to 2 mm in size) are transferred in the fall from the Institute's installation at Mohne Bay to tanks at the Power Station. Using the heated water from the Power Station, the young abalone grow four to five times faster than in the natural environment. When the abalone are 1 cm in size, they are transferred back to the tank farm at Mohne Bay. Lack of seaweed around the Power Station and costs for collecting or buying seaweed are the main reasons for moving them back to Mohne Bay at the l-cm size.
Because the preliminary results were so promising, the Power Station had built five new canvaslined, steel-frame tanks. Each tank, 20 x 1 x 1/2 m deep, can hold 60,000 seed abalone. Plans are to build up to 50 of these tanks in the next few years with a goal of producing 10 million seed abalone annually. All the equipment, including installation, is being paid for by the power company.
The sea scallop fishery reached its peak of production in 1934 when 80,000 metric tons (in shell weight) were harvested. Since then, production has declined and only 6,000 metric tons were produced in 1968 (Sanders, 1971). With the increased expansion of off-bottom culture, scallop production has been increasing in the past few years. The Japanese estimate that 40,000 metric tons would be produced in 1972 and possibly 100,000 tons in 1974.
In Mutsu Bay, the longline method of culturing scallops has been expanding in recent years. Here longlines are used not only for collecting seed but also for growing the scallops to market size. A scallop longline differs from those used in oyster culture in that there is a second buoyed line 3 to 8 m below the surface. It is from this lower line that seed collectors and cages for growing scallops are attached.
Scallop spawning in Mutsu Bay begins in March, peaks in early April, and is over by mid-April. The larvae life is about 35 days (temperature during this period ranges from 7° to 12°C). The fishermen put out their seed collectors in early May.
Initially, seed scallops were caught on suspended cyprus branches, but now over 50% of the collectors consist of plastic web bags filled with used gill nets. Eventually, most collectors will be of this type. In 1971, 2.3 million bag collectors were used and 40 billion seeds were collected in Mutsu Bay.
Before the young scallops lose their byssal threads, they are removed from the bags and placed in pearl nets. As the scallops grow, they are transferred to new pearl nets with larger mesh size. At about 4 cm, the scallops are either planted on the bottom or placed in circular or book nets and resuspended from the longline. The suspended scallops reach commercial size, 10.5 to 11.0 cm, in about 2 yr. It costs the fisherman approximately 14 yen/scallop to raise it to market size using the longline method. In turn, he can sell the scallop for 30 to 60 yen apiece.
Unlike the sea scallop fishery of the United States, the Japanese save all the scallop shells. These are bagged and shipped to the Inland Sea where they are used as cultch for catching seed oysters.
One of the principal laboratories involved in sea scallop research is the Aquaculture Center located on Mutsu Bay near the City of Asamushi at the northern end of Japan's main island of Honshu. The Center is a new installation that opened in April 1968. One of its largest programs is related to the propagation of sea scallops. Their goal is to produce 1 million seed scallops annually using hatchery techniques.
The Oyster Research Institute is also culturing sea scallops at their tank farm.
Scallops are induced to spawn using both natural and conditioned stocks. Over 200,000 seed scallops are cultured annually. They are suspended from the tank farm in book nets, circular nets, and pearl nets until a size of 2 to 3 cm is obtained. The scallops are then sold to local fishermen who grow them suspended from rafts. When the scallops are approximately 5 cm in size, the fisherman drills a hole in the ear (wing) of the scallop, threads a nylon line through the hole, and ties it to ropes suspended from rafts. They reach market size (12 cm) in about 2 yr (Costlow, 1969).
AUSTRALIAN FISHERIES.
1 Middle Atlantic Coastal Fisheries Center. National Marine Fisheries Service. NOAA. Oxford. MD 21654.