This paper describes an experimental large-scale, high-rise artificial reef designed by the authors with the intention of developing an offshore fishing ground in deeper waters and a large-scale, high-rise reef for practical use based on application of the results obtained from the experiments. The experimental reef, the world's largest artificial reef with a height of 35m and 4,000m³ in volume, is located 20km off Nezugaseki, Yamagata Prefecture, in the northem part of the Sea of Japan, in the neighborhood of a natural reef (Ohse Reef) known as an excellent fishing ground for red sea bream (Pagrus major). Observation by diving and trial fishing have shown that a large number of fish of various species gathered and stayed around this artificial reef. The reef is now being used in practical operation, and similar artificial reefs are being built in many other fishing grounds.

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Power spectral analysis of heart rate variability is used to determine activities of autonomic nerve system components regulating heartbeat in humans and other mammals. The power spectrum of heartbeat variability is associated with autonomic nerve system. High frequency components of power spectrum, in particular, represent parasympathetic (vagal) nerve activation. In this study, the power spectral analysis was applied to quantitatively evaluate fish physiological conditions through ECG recordings. Noise in actively swimming fish can not be isolated and the baseline of ECG is distorted making it difficult to obtain clear and continuous recordings. Maximum entropy method (MEM) was introduced to overcome this problem. MEM generates power spectrum clearly using relatively limited data to analyze heartbeat variability. Continuous R-R intervals were measured before and after subjecting the fish to hypoxia and anesthesia (using MS-222) to simulate increase and decrease of vagal nerve activity, respectively. It was observed that when vagal nerve was active the relatively high frequency component (0.3-0.5 cycle/beat) of the spectral power of heartbeat variability increased. On the contrary, when vagal nerve was inactive this component vanished. It is inferred that high frequency bands of spectral power of R-R intervals also represent the vagal nerve activity in fish.

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Intemal waves affect the physical environment in coast areas and a formation of mechanism of fishery ground. We theorized a transformation of the intemal inertial gravity waves by coastal topography and inspected using hydraulic experiments with rotary chamel. This theorized model used Holmboe's density model, which applied a mathematical model inserted a continuous layer in an interface of two layers, and added an effect of Coriolis force. The wave speed led by this model was arranged to simple practical forms and was agreed with the experiments. When the intemal waves progress in the shallow area, it was confirmed that the waves cause the shallow water transformation and are refracted due to the Snell's theorem. When a mass transport is generated by the shallow water transformation, it is recognized that the Coriolis force acts to the mass transport and makes the wave direction change. It is clearly that the wave height is estimated with the energy flux preservation law in a non-breaking zone. And the breaking condition of the wave was estimated theoretically. The characteristics of the intemal inertial gravity wave in coastal areas were determined using these theories.

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The barren ground, so-called Isoyake in Japanese, maintained at south-west coasts of the Sea of Japan, Hokkaido, Japan. In the Isoyake area, the sea urchin, Strongylocentrotus nudus, dominate on the bed rock, and occurrence of the kelp, Laminaria religiosa, was limited in the refuge at shallower zones. Fisheries in the coasts had large problem that the sea urchin could not grow up to the commercial size with inadequate foods. To develop the kelp forest technology in the Isoyake area, seasonal change of some environmental factors, water movement, water temperature, vegetation, and distribution of grazer, were observed continuously during 1998 to 1999 in Oshoro Bay. Environments for occurrence of kelp forest were characterized ; the sea urchins took refuge in deeper zone from strong water movement and buds of the kelp were protected from over grazing pressure during Winter. Moreover destructive pressure of the sea urchin occurred on kelp bed with no strong water movement and rock bed for kelp (amual algae) was protected from occupied of peremial algae during summer. We proposed two methods to increase the kelp forest in Isoyake area. 1) Seasonal control of excess grazing pressure using fence. 2) Adjust the depth with block and stone to remove the urchin by increasing velocity.

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漁業技術の発達は,漁獲能力の向上によってもたらされると考えられていた。しかし,漁獲能力が著しく 向上すると,漁業技術の発達は有限な資源と対立する。北海道東部地域における2種の桁網漁業(ホタテガ イ桁網漁業とホッキガイ桁網漁業)では,漁獲能力の向上に伴う乱獲問題が発生した後,漁業技術が資源管 理に適した形に変化した。この報告で筆者は,そうした技術変化の内容と背景を明らかにし,技術発達が漁 業者間の協力関係の形成に基づく資源管理に適合的な方向に向かうことを指摘した。

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This study examined the effect of the pneumatic submersible system on saving labor and scallop growth in depth control work of scallop cultivation facility, in case of practical use scale, in Mutsu Bay, Japan. The experimental results showed that the pneumatic submersible system reduced working time by 36 % , working time by 52% when excepting the operational mistakes, working time per unit operation by 48 %, number of operation per unit facility by 20%, and didn't affect the mortality and growth of scallops.

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In this study, I discuss a method to measure the bottom material hardness using a digital force gauge. I conducted the field observations of the bottom material hardness along the Niigata coast. Values of the penetration resistance of the force gauge per 5cm depth into the bottom material ranged 0.81-5.72 N. The penetration resistance was higher than l.4 N in sandy mud bottoms. Muddy bottoms were classified into soft (< 1.4 N) and hard (1.4 -3.0 N) categories. The density of the benthic fauna in muddy bottoms was lower for hard categories than for soft ones. These results suggest that the hardness of the bottom material is one of the important factors of the bottom environment which affect the benthic fauna.

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The use of an acoustic-sound feeding method to enhance the colonization of marked and released, cultivated juvenile grouper, Epinephelus akaara, was investigated around artificial reefs off Shiraishijima Island in the Seto Inland Sea. During underwater observations from May 1996 to December 1999, 35 species of fish were observed around the artificial reefs and the fish biomass varied from 19 to l,247g/m³. Three species, E.akaara, Sebastes inermis and Sebastisucs marmoratus, dominated the fish community, and the biomass of each species varied among months. Although the number of juvenile grouper remaining in the area dramatically decreased on the first day of their release, 43.7% of the one year old fish remained where they were released on the artificial reef after one year. Furthemore, 2-4% of the released grouper remained on the artificial reefs two or three years later. Counts of juvenile grouper, however, varied significantly among both observation months and the reef sites. Yet, on the central part of the artificial reef where the acoustic-sound feeding method was used, the number of released grouper was significantly higher than at sites on the periphery of the reef. These results suggest that acoustic-sound feeding systems associated with artificial reefs enhance colonization of released grouper. Such methods increase wild and cultured fish populations in the nursery grounds.

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