The possibility of equalizing the length of time for daily work was, in the preceding report, eXamined using the records of 139 strings, which were extended along a nearly straight course and taken from 392 records obtained from a research tuna longliner in 2 years in the eastem mid-Pacific. These records covered 35.4% of the available records. The coverage of the records was increased to 90.6% ( = 355 strings) by including those extended along a curved or meandering course. They were classified into 23 groups with respect to position, season and gear construction. It took about 5 hours to extend a string with 2,400 hook droppers and 12.5 hours to retrieve it on the average. The observed time length of each operation was compared with that estimated from either the group average of the speed or the regressive relation of the speed to the number of sections, slack in the mainline and wind speed. Setting a difference of less than 10 min for extending work and 30 min for retrieving work was within the permissible range, the times for extending 85.6 % of the strings and that for retrieving 68.5% could be expressed by using the group average of the speed. These rates increased to 91.0% and 77.7%, respectively, when the observed time length was compared with that using the regressive relation. The strings showing a difference in the time length over the permissible range were concentrated in 4 groups for the extending time and in 10 groups for the retrieving time. The former suggested the dependence on the number of days fishing. For the latter, the reason for the difference between these groups and others has not been clarified yet. These results suggested the possibility of equalizing the time length of daily work by adjusting the length of the string according to the predetermined conditions.

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The theoretical formula of three stratified interfacial long waves are deduced and its validity is verified by the experiment. The three stratified interfacial long waves consist of two modes that are Mode I and Mode II. These waves velocity are expressed c_I and c_II in equation (1') respectively. The wave numbers of these waves are expressed k₁ and k₂ in equation (3). These stratified interfacial wave profiles of first and second interface are expressed ζ_I1, ζ_I2, ζ_II1 and ζ_II2 in equation (8) respectively. The water particle velocities of these waves in first, second and third stratified layers are expressed u_I1, u_I2, u_I3, u_II1, u_II2 and u_II3 in equation (9) respectively. These relations between the profiles and the velocities are shown in figure 2.

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This paper presents details of a second order accurate Godunov-type numerical model of the two-dimensional shallow water equations and shows the application of the model to flow in a vertical sIot fishway. The model employs Roe's flux function for the convection tems and a non-linear slope limiter to prevent unwanted spurious oscillations. The model is also based on quadtree grids that adapt to inherent flow parameters, such as depth-averaged vorticity. Three test cases are demonstrated using a typical vertical slot fishway. The first test case uses relative coarse numerical grids and the second uses fine grids. The third one uses solutio-adaptive grids. Comparing the results between the first and second cases, it is shown that the results largely depends on the size of grids in interior flow region, even though the flow boundaries are fitted correctly by quadtree grids. Through the comparison between the results of second and third cases, the advantage of solutio-adaptive grids is demonstrated.

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The differential Global Positioning System, DGPS, improves the user positioning accuracy based on correction data computed of the reference station. The offset of the reference station, which includes an absolute position erro, influences the user positioning accuracy. In addition, it is thought that in case of constructing a personal DGPS system, the absolute accuracy of reference position influence user positioning accuracy. Authors applied an intentional offset to the reference position, and quantitatively tested the influence of the reference station offset on the user positioning. In this experiment, one GPS antenna was connected two GPS receivers (one was for the reference and the other was for the user). DGPS measurement was done the baseline 0 m so that other positioning error factors (e.g., multipaths, ionospheric delay, etc.) would not affect this experiment. As a result, the reference point offset corresponded to the user measurement in the offset distance and direction. In the case of constructing a personal DGPS, the absolute position of the reference station must be bighly accurate.

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This paper reports on the development and testing of the new type seawater intake works using wave energy. The one is 'the seawater intake works with cylindrical holes',. one of the most important characteristics of the works is to having the aeration ability for the improvement of aquatic environment. A hydraulic model test on the works was conducted in the basin and in the channel. The adequate specifications of the works had to be found by trial and error. According to the various studies, the works has proved to be good enough. The main results are as follows : (1) The works with 10 meters length has the ability of training seawater 40,000m³/day when the coastal waves has the condition that is head incident, 0.5 meter significant wave height and 4 seconds wave period ; (2) In case of the tide level locates the quarter diameter below from the center of the cylindrical hole ; the works functions the most effectively ; (3) The reflection coefficient is 0.63 to 0.65 ; the transmission coefficient is no detected in random waves ; and (4) When the ceiling slab cIoses the wave chamber, the air duct with 0.5 to 1 percent of the ceiling slab area must be constructed to prevent air compression.

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Propagation of the seagrass, Zostera marina, was examined by using artificial seeding methods on polypropylene mats named as a sediment stabilizer mat (SS-mat) used to decreasing sediment disturbance on the sand substratum off Kushiki, Naruto, Tokushima prefecture, eastem Seto Inland Sea. SS-mats (1m x 1m, 4cm, 23 and 31kg of weights) were made of pemeable meshes. The first experiment was started in autumn, 1995 and the second experiment in autumn, 1996. Plants of Z. marina, seeded on to the mats, grew successfully for four years even under a harsh environmental condition of high wave height and fluctuations of the sand bottom level in the winter season. In both experiments, the shoot density on the SS-mats was observed to decrease after the maximum number of individual shoots (50-60 shoots/m²) in the first summer season to several shoots/m² in the 2nd and 3rd summer seasons. Z. marina plants made reproductive flowering shoots on the SS-mats since 2nd spring maturing period. The SS-mats were useful in germination of seed and growth of seedlings for Z. marina, but not useful for the survival of adult plants due to the lack of sand accumulation on the mats. Such long term monitoring of continuous growth of Z. marina plants on the SS-mats is required for promoting the methodoIogy of establishing sea grass beds restoration.

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Ammonia removal was studied using a submerged filter and a rotating bioｌogical contactor (RBｌC) with an interlocked fiber medium. Experiments were carried out to examine the effect of flow rate on the ammonia removal rate with a submerged filter and the effects of physical parameters (flow rate, submersion ratio, and rotational velocity) on the ammonia removal rate in an RBC. In the submerged filter, the ammonia removal rate increased in proportion to the hydraulic loading rate in the range of 80-640 m³/m²/day. In the RBC, the ammonia removal rate was high at rotational velocity range of 12-18rpm (peripheral velocity, 0.094-0.14m/s) and at a submersion ratio of 40% or more. Conceming flow rates, while an increase was observed with increasing flow rates, the actual differences were minimal as compared with the submerged filter. When the influent ammonianitrogen concentration was fixed at lmg-N/L, the ammonia removal rate was higher in the submerged filter, peaking at 0.25g-N/m²/day (flow rate, 240L/h), While the RBC's maximum was 0.15g-N/m²/day (rotational velocity, 12rpm ; aubmersion ratio, 50% ; flow rate, 120L/h).

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This study examined the effects of bottom disturbance associated with wave action on the burrowing behaviors of the surf clam Mactra chinensis (shell length = 28.5 - 85.0mm) using a vertical circulating water channel. The burrowing speed of the clam tended to increase with shell length and Shields number as an index of bottom disturbance regardless of burrowing posture toward water flow. The relationship between the burrowing speed (V : mm/s), Shell length (L : mm) and Shields number (ψ) was described as V=0.022L+5.989ψ. A large number of the clams apparently burrowed with orienting their lateral toward the flow. The critical conditions when the clams could not burrow into the sand and would be washed out of the sand by bottom disturbance were shown as functions of the shell length and Shields number with ψ =3.087×10^-4L＋0.081 and ψ=0.004L＋0.099, respectively. The critical Shields number to wash the clams out of the sand corresponded to that of shallower limit of water depth in the clam habitat.

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We attempt to inhibit the accumulation and proliferation of marine fouling organisms on vinyl plates through application of a weak electric current via a titanium wire electrode. Plates are set in two sea areas near the National Fisheries University ; one area is subject to an electric current, and the other area is used as a control. The experiment was carried out over two periods ; July and August 1998 (2 months) and September to January 1999 (4 months). The electrode was a platinum-coated titanium wire of 0.5mm diameter twisted with a polyethylene rope. Using solar cell modules and rechargeable NiCad batteries, we supplied a constant current and voltage during both periods. It is found that an electric current of 20mA at 2.5V is not sufficient to effectively prevent the adhesion of marine fouling organisms, whereas the application of 50mA at 5V is effective in preventing the adhesion of bamacles.

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The mean fish body length, the fish body weight and cultured fish number per unit volume of the pen are estimated from the practical fish culture data of yellowtail, sea bream and so on. Depending on these data, the relationship between the body length and body weight and numbers of cultured fish per unit volume of the pen are clarified. Moreover the dissolved oxygen consumption by fish per unit volume of the pen are discussed.

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