This paper proposes a method for estimating an in-water image contrast using its black-and-white photograph. Contrast values Ci of 26 test boards, each of which has specific coloring composition against black background, were estimated from the proportion of their luminance values under different intensities of illumination ranging from 1500lx to 0.03lx. In other method, each of the test boards was photographed using black-and-white film with different sensitivities based upon the light conditions. Using the particular computer software and scanner, the specific gray values of both target and background for each image photograph were obtained to estimate the comparative contrast value Cg. Results show that increasing light intensities did not enhance the contrast value. In comparison with the contrast estimated from the two methods a relative equation between the Cl and the Cg is presented as : Cl= 0.174 ln Cg十0. 921. Application of this equation to data for the in-water photograph was also discussed.

抄録全体を表示

The stratified intensity of water column can be estimated by measurements of temperature, salinity and density gradients between the upper and lower water layer, but the quantitative method using the Vaisala frequency or potential energy has been proved more efficient. The potential energy method was applied in this study for Uranouchi Bay (southem Japan): (1) The water column's stratified intensity was a combination of potential energy by temperature and salinity. The latter, however, appeared to have more influence on stratification. (2) The seasonal change in stratified intensity consisted of short (1-2 months), and long period (1 year), corresponding to salinity and temperature changes, respectively. (3) Beside solar radiation and precipitation, mixing by intemal waves also influenced stratified intensity. (4) The estimation of stratified intensity with potential energy is effective in expressing the phenomenon of dissolved oxygen deficiency of bottom water.

抄録全体を表示

In spite of a widely accepted trend of settling large-scaled artificial reef groups, the structure of the actually settled ones is scarcely verified, because the suitable equipment was hardly available until recent. A survey by using highly sophisticated electronic devices was conducted in October 1991, off Nagato for the 13 groups of artificial reefs settled. And the following results were obtained : The side scan sonar (500kHz, 150m range each side) was proved to be very effective for the present purpose, as supported by the fact that as many as 95% of the component reefs could be detected by sailing at 3.5 knots along parallel courses of 200m intervals. Most of the component reefs in the circle type groups were found within the planned range, while the aberration of their settled positions in the pseudo-ellipse type reef groups was mainly due to that of center blocks settled by hanging methods basing on the indication from Loran C.

抄録全体を表示

Researches to clear the cause of death or decrease of population of Japanese littleneck clam in winter Were conducted. Environmental factors for the clam, such as water temperature, chlorophyll-a, low salinity, and ground-level movement by wave were investigated on Banzu tidal flat in Tokyo Bay from 1991 to 1992. Water temperature in the tidal flat waters ranged from 5℃ to 15 ℃ during investigation period, and the fluctuation in shore-side of the flat were larger than that in off shore-side. When chlorophyll-a increased in the Waters off the flat, clorophyll-a, condition factor and burrowing rate of the clam on off shore-side of the flat increased, but not on shore-side of it. In addition, survival rate of the clam on shore-side of the flat decreased gradually. When salinity less than 16 continued for more than four days, the clam began to die in laboratory experiment. But, on the tidal flat, low salinity continued for only less than two days. The highest value of the ground-level movement by wave was - 5cm for 24 hours on off shore-side of the flat. It was considered that the clam become inactive with low temperature and by decrease of phytoplankton. Weakened clams may not keep burrowing in substratum and will be dispersed by wave action, and consequently, the population decreases in culture ground.

抄録全体を表示

Behaviour of the Japanese striped knifejaw Oplegnathus fasciatus was studied by underwater observation and tagging experiment at Tajima coast in Japan Sea. The results obtained are as follows ; 1) The fish schools were small on the rocky reef, but were large on the artificial seaweed farm plant. 2) High rates of schooling were shown in juvenile and young fish respectively, both on the artificial seaweed fam plant and on the rocky reef. The rates of schooling on the artificial seaweed fam plant were higher compared with those on the rocky reef. 3) Approximately 92 % of tagged fish were recaptured within l0 km from the released point. 4) It was suggested that small schools and solitary individuals on the rocky reef were sedentary and large schools were migratory. It was also suggested that large schools on the artificial seaweed farm plant were staying there temporarily. 5) An unfavourable environment as sandy bottom seemed to force the fish to aggregate on the structure like the artificial \SeaWeed farm plant and the artificial reef. On the other hand, the large schools broke into smaller ones on a favourable environment as the rocky reef and the fish stayed there for a long period of time.

抄録全体を表示

Using a fence designed to obstruct the movement of the shortspined sea urchin, Strongylocentrotus intermedius, and the northem sea urchin, Strongylocentrotus intermedius, the characteristics of their behaviors on different substrates, and their behavior on horizontal and vertical plates were observed. Five kinds of substrates were used (i.e. acrylic, cloth, sponge, and 2 kinds of net). On these substrates, their moving force and speed were measured. Using a video camera, sea urchins positioned on a horizontal plate or at one side of a vertical plate were observed moving across the plates. For both species, the moving force and speed on the acrylic board were highest, i. e. 270 gf and 2.9 cm/s for the short-spined sea urchin, and 417 gf and 5.0 cm/s for the northem sea urchin. The lowest values for the short spined sea urchin were 27 gf and 0.6 cm/s on sponge, while the lowest for the northem sea urchin were 45 gf on sponge and 2.5 cm/s on net. The sea urchins could move easily across the plates. After observing the moving behavior of sea urchins, it was considered that the kinds of substrates and the urchin's position on a plate are not factors which obstruct the sea urchin movement.

抄録全体を表示