The temperature, salinity and contents of dissolved oxygen on the plane of 40 in deep were chosen as the examples of the environmental factors. The first one is the representative of physical factors. The second one is of the chemical one of conservative nature, and the last one is also chemical one, but changes according to the conditions and sometimes limits the distribution of fish. As example of the condensed information, for the number of layers to be illustrated is limited, σｔ was chosen.
No symptoms suggesting the presence of clear boundary of water masses or discontinuous water masses were suggested from their distributions. This fact meant that there were no need to treat the data after stratification into some sub-groups. The gradient mainly in N-S direction was found in both of the two factors of oceanographically fundamental importance, the temperature and salinity, suggesting the inverse relation between them. This fact meant that, if one of them was adopted as explanation variable, it was less probable that the other was adopted as the second one. And the choice of either of them as explanation variable should be done carefully basing on the results already found in other reports. An inadequate choice may bring into confusion.On the contrary to them, the contents of dissolved oxygen showed the decreasing trend towards east. without showing any stagnant areas. This trend is somewhat parallel to the depth. If increasing trend with decrease in the contents were found in the distribution of groundfish. the practical meaning of the results obtained should be examined basing on the habit of the fish detected.
These are the examples of suggestions from overlay maps. to which full attention should be paid in the analysis of the relation between Sa and environmental conditions.
As described above, it may be concluded as follows: Introduction of GIS technique into marine science assists very much in making it easy to find many valuable information, to which full attention should be paid in analysis of the effects of artificial reefs on the distribution of fish. And adequate use of this technique may improve very much the reliability of the results of analysis. in which the spatial distribution of original data is apt to be not taken into account.
ACKNOWLEDGEMENT
The authors are thankful to Emeritus Professor Dr.H.Maeda of the National Fisheries University for his constructive advise.
REFERENCES
1) K.Uchida, A.Hamano, S.Sanetoh, S.Tatsumi and T.Tateishi: Evaluation of settled position of component reef blocks in an area with some large-scaled artificial reef groups detected by side scan sonar. Fisheries Engineering, 32, 13-22(1995) (in Japanese with English summary).
2) K.Uchida, A.Hamano, H.Maeda, K.Kubota and K.Tabuchi: Distribution of fish assembling around 54 large-scaled artificial reef clusters settled in an area. Proceedings of international conference on ecological system enhancement technology for aquatic environ ments. Vol.1. 18-23 (1995) (in Japanese with English summary).
3) Y.Simard, D.Marcotte and G.Bourgault: Exploration of geostatistical methods for mapping and estimating acoustic biomass of pelagic fish in Gulf of St.Lawrence: size of echo-integration unit and auxiliary environment variables. Aquatic Living Resources, 6, 185-199(1993).
4) J.Castillo, M.A.Barbieri and A.Gonzalez: Relationships between sea surface temperature. salinity, and pelagic fish distribution of northern Chile. ICES Journal of Marine Science, 53, 139-146(1996).
5) R.Kieser and G.Langford: An application of spatial analysis to fisheries acoustics. In Proccedings.GIS '91 Symposium, Vancouver, B.C., 335-339(1991).
6) K.Foote, H.Knutsen, G.Vestnes, D.MacLennan and J.Simmonds: Calibration of acoustic instruments for fish density estimation: a practical guide. (Cooperative Research Report. ICES No.144, 57pp(1987).
7) G.J.Meaden: Potential for geographical information systems(GIS) in fisheries management. In "Computers in fisheries research" (ed. by B.A. Megrey and E.Moksness). Chapman & Hall. London, 1996, pp.41-79.
8) R.Kieser, K.Cooke and G.Langford: Recent developments in spatial analysis of fisheries acoustic data. In Proccedings GLS '92 Symposium. Vancouver. B.C., 1-4(1992).
