To secure labor for fisheries in Japan, it is necessary to investigate the actual working conditions of fisheries and redesign the tasks so that the work is reasonable. This paper quantitatively analyzed fisheries work on a small trawler working out of Choshi in Chiba Prefecture. All of the movements of the crew on the quarterdeck were recorded using a video camera and a hard disk recorder during a fishing trip. The recordings were sorted, and the times required for each task were measured. Physical loads on the crew were estimated using the Ovako Working-posture Analyzing System (OWAS), a popular approach that is based on the work posture of a subject. The trip was about 26 hours long and the crew were worked on the quarterdeck for about half of this time. Approximately 25, 24, and 7% of the casting, winding, and sorting work respectively, were judged as harmful and needing to be improved. The workload was roughly similar to the instances in primary industries, but higher than those in secondary industries.

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The shortening ratio, defined as the ratio of the horizontal distance between two neighboring floats to the mainline length, is one of the important factors in settled hook depth in tuna longline. Because it was difficult to measure the distance between floats, apparent shortening ratio was estimated from a log in shooting. The purpose of this study is to investigate the drift pattern and actual shortening ratio of a tuna longline using GPS buoys to determine the position of floats of a longline during drifting. The longline research cruise was conducted by Japanese R/V Shoyo-Maru in eastern area of northeastern Pacific Ocean in the period between September and November 2004. In this study, a total of 583 GPS buoys were used which measured the distance of 179 given baskets. Drift patterns of a longline are classified into two types. One is a parallel track to the shooting course, and the other is a meandering track. There is no relationship between the drift pattern and the variation in actual shortening ratio. Actual shortening ratio on 70 to 90% of total 179 baskets shows a different value from apparent shortening ratio without relation to drift pattern.

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フィリピンのパヤオ(浮魚礁)周辺で,キハダ幼魚の腹腔内に超音波発信機を挿入して放流し,パヤオのアンカーラインに装着した受信機で行動をモニタリングした。キハダ幼魚はパヤオ周辺にとどまり,同時にモニタリングした同サイズのツムブリに比べ,明らかに深い層を遊泳した。夜間は比較的浅く狭い層を遊泳し,昼間は深く広い層を遊泳する日周性や,深夜にパヤオから離れるなど,これまでに報告されているキハダ成魚とよく似た行動を示した。再捕結果から摂餌や移動が確認され,キハダ幼魚のテレメトリーが可能であることが示された。

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This study was carried out to examine the negative effect of penetration resistance (PR) of the sediment on burial ability of the Japanese littleneck clam Ruditapes philippinarum. In the laboratory experiment designed to estimate the critical PR for burial ability of the clam, relative burial depth and burrowing rate were compared between following PRs given to the sediment: 0.13, 0.24, 0.41, 0.55, 1.57 and 2.16MPa. In addition, PRs of the sediment, coupled with other variables such as median grain diameter (d_<50>), sorting coefficient (σ_1), mud content and water content, were measured in 12 fishing grounds of the eastern Hokkaido, Japan. No significant correlation was detected between PR and relative burial depth of R. phillipinarum, whereas burrowing rate significantly decreased when PR increased from 0.24 to 0.41MPa. Multiple regression analysis revealed that PR was best predicted with a combination of 3 variables, depth from the sediment surface (h), d_<50> and σ_1. These results suggested that burial ability of the clam in bottom disturbance due to erosion and deposition would be lowered when burrowing rate was limited by sand compaction. In conclusion, the combination of h, d_<50> and σ_1 could be a useful indicator to evaluate the suitability of the sediment for burial ability of R. philippinarum.

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To clarify the difference of fish species attraction to artificial fish reefs according to the structure of fish reef units, fish catch experiments were performed at different reef units and a control area arranged in Furubira-cho offing, Hokkaido. The attraction effect of the fish reefs for each fish species due to differences in structure was ascertained by use of principal component analysis (PCA). As a result, accumulated contribution ratio of the directivity for the element of fish reef unit accounted for 89% and the main characteristics were explained by just four components. It was suggested that the characteristics of the attraction effect for each fish species were different among the types of the fish reefs.

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Time variations of coastal bathymetry and sand grain size were investigated at the north Kashimanada Coast, a 40km long section of coast located between Oarai Port and Kashima Port. From the change of coastline position obtained from aerial photographs in 1975 and 1984 and bathymetrical surveys from 1984 to 2004, it was found that the beaches located just next to Oarai Port and Kashima Port had been depositional and the areas next to those depositional beaches had been heavily eroded. The central area of the Kashimanada Coast was shown to be slightly depositional. Grain size distributions at the shoreline obtained from surface layer samplings in 1982, 1998 and 2003 showed a tendency that grain size became coarser in the eroded areas and that the areas were expanding. From analyses of the bathymetrical surveys, it could be considered that in almost 2/3 of the coast, offshore longshore sandbars diminished from 1984 to 2004. From the long-term change of distributions of juveniles of Hard Clam, Meretrix lamarckii, along the Kashimanada Coast, it was found that the number of juveniles had been remarkably reduced since 1996 and that juveniles are now distributed at only the depositional beaches next to Oarai Port and Kashima Port, whereas in 1993 and earlier, juveniles were distributed in wide areas of the Kashimanada Coast, especially at the central area. From the coincidence of the areas of beach erosion, grain-size increase, sandbar extinction and decrement of number of juveniles, those changes of physical environments were considered to be responsible for the loss of juveniles at the Kashimanada Coast. The continuous change of the environment suggests that the suitable habitat area for juveniles of the Hard Clam may be further decreased.

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Input-output tables are useful in analyzing problems and tasks based on the industrial and economic structures in fishing villages. We compiled input-output tables for five regions in Hokkaido (Rausu, Akkeshi, Nemuro, Tomamae and Minamikayabe) and the economic effects resulting from changes in the industrial structure and the promotion of new industries to address regional problems and measures aiming to address other future problems were calculated by inputting variables to the tables. This research aims to highlight the mutual issues facing fishing villages and fisheries in addition to the unique issues confronting each fishing village by comparatively analyzing the characteristics of the present industrial structure for the aforementioned five regions, so that the most effective measure for each region could be assessed.

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