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.
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.
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.
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.
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.
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.
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.