The Award of the Japanese Society of Fisheries Engineering 2007 was given for the comprehensive study on hydraulics of coastal fishing grounds. This study is made up of three parts, which are the characteristics of variability of bottom layer fiow in coastal sea area, the environmental conservation of coastal tidal lagoon and the characteristics of the flow in stratified bay. The first is for the establishment of design guideline of estimation of bottom current for the structures on sea bottom such as artificial fish reefs. The second is to make rough estimation of material balance and to establish the conceptual framework of material circulation model in Lake Saroma. The third is for the estimation of flow pattern and seawater exchange by internal tide in Gokasho bay. In this paper, the purpose, means, results and outcomes of the study are outlined.
This manuscript summarizes the results of our paper, which has been awarded by the Japanese Society of Fisheries Engineering, on the process of the mortality of Japanese littleneck clam (Ruditapes philippinarum) due to large winter waves. The major finding of the pap-er is negative influence of the frequency in the clam exposure to the seabed surface and the burrowing rate on glycogen content and condition factor as indicators of energy store. We also suggest other factors affecting the abundance of clam resources such as warmer water temperature in winter and discuss methodology to stabilize the clam resources in future.
The distribution of the fishes in the circumference of fish reefs varies with fish species. Furthermore, it changes with forms and volume of fish reefs. The relation between the distance x and the fish catch index q which were obtained by the fish catch experiments classified by distance from artificial reef unit was applied to the approximation formula q=f(x). Moreover, the fish catch index F, for flat ground was determined. Thereby, the distance of the effective range in which an artificial reef unit brings fishes together was determined by the intersection of q=f_c, and approximation formula q=f(x). Furthermore, the distribution of white-edged rockfish fished by two artificial reef units having different volume was compared. Consequently, it is suggested that the effective range become increase with the volume of reefs.
Midwater float for pelagic longline consists of plural additional small fioat, which keeps the depth of each hook to the same layer, and this study presents three-dimensional shape of longline with the midwater float in uniform stream, by model experiment in a flume tank and by numerical simulation based on finite element method Each part of longline was shoaled by the current, and then the depth of the hooks became shallower with the faster water current. In particular, the principal factor affecting the hooks shoaling was the spread of horizontal spacing between the two successive buoys by the faster current. When the longline was cast with a given angle to the stream, the longline gear had threedimensional structure, and then the hooks were set at much shallower depth. The numerical calculation simulated well the shoaling of the longline in the flume tank. The comparison of the numerical simulation in longline shoaling between the midwater fioat setting and the conventional setting suggested that the depth of longline with the midwater float was susceptible to the current. The possible reason was that the in-water weight of the longline gear was lightened by the midwater float, comparison to the conventional setting. For setting the hooks at the target depth in water current by using midwater fioat, the simulation of longline shoaling was useful to determine the specification of the midwater float system, e. g. the number and buoyancy of the midwater float, and fioat line length.
A trousers-type framed midwater trawl (T-FMT) was developed for the simultaneous sampling of plankton and micronekton, which allows the use of two kinds of mesh sizes at the same time. This paper describes the performance of T-FMT in the survey of plankton and micronekton. In addition, the estimation of size selectivity for these small creatures was conducted by using the SELECT analysis expanded for a sub-sample from the trousers trawl experiment. The experiments for plankton and juvenile walleye pollock were conducted offshore of Usujiri, Hokkaido. Three kinds of codends were prepared: two moji-nets with mesh sizes of 1.7mm (M17) and 3.1mm(M31), respectively, and a plankton mesh with a mesh size of 526μm (PL). A pair of codends, M17 vs. PL and M17 vs. M31, was tested for sampling plankton and juvenile walleye pollock, respectively. Euphausiids dominated the catches of the M17 codend, whereas copepods were dominant in the PL codend. The Iength distribution of euphausiids in the PL codend showed a bimodal shape, whereas of those in the M15 codend showed a unimodal shape. The average L_<50> and S. R. values for the estimated selectivity curve of the M17 codend for euphausiids were 7.8 and 1.0mm, respectively. For the juvenile walleye pollock caught in April (early season after spawning), the length distribution in the M17 and M31 codends showed a deviant shape, i.e. there were no fish smaller than 12mm in length. For the fish caught in June, the length distributions for the M17 and M31 codends showed a unimodal shape, and there was no difference in length distribution between the M17 and M31 codends. Based on these results, it was concluded that the PL and M17 codend pair was suitable for the simultaneous sampling not only of plankton and micronekton but also of juvenile walleye pollock in this area from April to June. In addition, the availability of T-FMT in the study of size selectivity for small creatures was confirmed.
When oyster shells generated through oyster culture are placed on the ocean floor, it is understood that the shells have a positive effect on the improvement of bottom quality as well as a stabilizing effect on the growth of eelgrass. In Okayama Prefecture, the focus is being put on the effectiveness of oyster shells. Various examinations designed to quantify the effects of placing oyster shells on the ocean fioor are being carried out so that oyster shells can be put to practical use as a material for improvement of bottom quality in ooze see areas and to aid in the creation of tidelands and seaweed beds. Through these tests, it was demonstrated that the quality of the bottom was improving and that, along with the diversification of benthos, the survival rate of eelgrass was rising. "Guidelines for the Effective Use of Oyster Shells" were formulated in order to address concerns surrounding the use of oyster shells. Some such concerns included the necessity to clearly draw the line regarding rules on waste disposal in the ocean, intended uses and procedures for laying down shells based on the results up to this point. This report will discuss the progressions and results achieved thus far of verification tests conducted up until this point. Together with this, this report will discuss more about the contents of the guidelines and the future development of these findings.
The prevention of global warming and environmental destruction, furthermore the formation of sustainable development society is both important and indispensable. The present society of mass production, consumption and disposal must rapidly replace to the recycling-oriented society. Therefore, it is necessary to form the fishing ports and the fishing villages to be compatible with the recycling-oriented society. Above all, in the fishing port and the fishing village area, the various waste biomass resources are generated from the fishery production activity and the fishing village community. As effective use of waste biomass resources generated in the fishing port and the fishing village, there are farmland use, energy use, construction materials use, and product use, etc. For example, one of the realistic and effective uses is compost in green space and farmland.
The promotion of the action for the construction of the recycling-oriented society is one of outcomes of the fishery infrastructure improvement project. For the construction of the recycling-oriented society in the fishing village, the promotion of material recycle is understood as one of main purposes in the fishing port and fishing ground long-term development plan. For the positive promotion of material recycle, it is very important to process the fishery by-product such as shells that is discharged in large from shellfish aquaculture. In this paper, the important points on practical use of recycled materials were shown for not only the fishery by-product but also the by-product which occurred from the other industry. The legal, institutional and technological problems of various recycled materials were reviewed. The future prospect of practical use of recycled materials was shown.