Fig.2 Location of the points of laser position fixing system.
3. RESULTS AND DISCUSSION
3.1 Artificial reef clusters detected
The principal aim of the present report is to show the effectiveness of GIS in the analysis of the effect of artificial reefs on the distribution of fish, via the environment conditions, which were modified by the artificial reefs. Accordingly, as the base, a short description about the detected distribution of them was given here: According to the plan, 8 clusters ( 7 of high construction and one scattered, each within a radius of 125m around the planned center, 6396m3 in a total volume covered ) were settled in 1984 to 1989 in the area of 3,750 × 2,500m in on the sea-bed of 55 to 62m deep, as shown in Figs. 3, 5 and 6.
As the results of survey, the presence of as much as 96%1） of component blocks could be detected out of 305 × 7 + 293 ones of various types settled. All the center blocks were found at 186m (on the average) northwest of the respective planned positions. In spite of this fact, the relative position and arrangement of copmponent blocks could be regard to be within an acceptable range from practical point of view as shown by the fact that 86% of the detected components were found within the planned radius in nearly the planned arrangement.
3.2 Oceanographic conditions
Here, a short description about the vertical distribution of temperature and salinity was given, for reference, because overlay map drawn by GIS technique in Figs.5 and 6 can not cover the vertical section of respective factors drawn.
Fig.4 shows the vertical sections of temperature and salinity along Line D in May and October of 1995. In May, the temperature showed a small vertical difference ranging from 16.55℃ at surface layer to 15.95℃ near sea-bed. Salinity showed high values, when the local mean was taken into account, ranging from 34.40 at surface layer to 34.60 near sea-bed. Along with these findings, flowing of water of higher density in the deeper layer towards the coast was suggested from Fig.4. In October, on the other hand, the temperature showed relatively large vertical difference, from 22.0℃ at surface layer to 19.9 ℃ near sea-bed.
3.3 GIS graphics
The indispensable prelimina｣? step to examine the effect of artificial reefs on the distribution of fish is the choice of explanation variables and the examination of the bias of spatial distribution of them and objective variables and the presence and location of discontinuously high (or low) values. In spite of the fundamental importance of this preliminary step, it was not in common to examine, to stratify and to screen the data before the analysis. This may be due to difficulty in illustrating the related factors in an easily understandable form all together, within a reasonably short time and labor. The GIS technique is one of the most suitable tactics for this propose as reader can understand easily from Figs.5 and 6.
The bottom topography, in which the distribution and form of the artificial reefs are included, is shown in the floor of Figs.5 and 6. This is the basic information probable to cause heterogeneity in the distribution of fish. The induced result, which is the distribution of fish, was picked up as the mean surface area back-scattering strength (Sa) using the quantitative echo-sounder, and is shown in the floor just above it. The results differed according to the month. In May, no correspondency could be found between locations of reefs and Sa, because of rather uniform distribution of Sa. And these data were not suitable for the analysis of the relation of Sa to any of the environmental factors, when the distribution of Sa in very small scale was dealt. In contrast with the results mentioned above, in October, a good correspondency was found between the locations of reefs and high Sa, although some discrepancy was found between the size of reefs and value of Sa.
