There is a growing need for ecosystem-based fisheries management. Proper assessment and management of the impacts of fisheries on non-target (bycatch) species are required. Scientists have conducted various research and development to solve the issues in the interaction of tuna longline fisheries with the bycatch species worldwide. Recently, tunas Regional Fisheries Management Organizations (RFMOs) have implemented Conservation and Management Measures (CMMs) for bycatch species (e. g., seabirds and sea turtles). In Japan, the author have developed and evaluated various mitigation measures for reducing bycatch and/or mortality of seabirds and sea turtles in tuna longline fishery. The present paper introduces several approaches of the bycatch mitigation measures (tori line and side setting for seabirds, and circle hook, bait modification and de-hooking device for sea turtles) based on fishing gear technology, highlighting some interesting topics.
To restore macroalgal beds in sea urchin-dominated barren areas, concrete blocks were placed and seeded with germlings of several Sargassum species at a wave-sheltered shallow site off Sakinoyama, Kasasa, Kagoshima, Japan in 1999. This resulted in a remarkable extension and long-term persistence of Sargassum beds, without removing urchins. Previous studies suggested that thin sediment cover might exclude sea urchins and allow the recruitment of sediment-tolerant species such as Sargassum duplicatum. Field studies were added to understand the mechanisms for the establishment of Sargassum in more detail. Transect surveys suggested that sea urchins including long-spined Diadema spp. having high mobility do not move into the area with >50% of even thin sediment cover, although shorter-spined Echinometra sp. translocated to small blocks within sand-covered areas moved over sand. Survivorship of caged Sargassum germlings on cobbles translocated to sediment-free urchin barrens were considerably lower than the previous observations in sedimented Sargassum beds, suggesting that thin sedimentation might prevent herbivory not only by urchins but also by mesograzers. However, outplanting S. duplicatum germlings suggested that thin sediment cover might not ensure their survival due to other factors such as feeding by sandy bottom organisms. Maintenance and recent reduction of Sargassum stands are also discussed.
Marine structures like cylindrical bridge piers are exposed to hydrodynamic force F (=F_M + F_D, where, F_M is mass force and F_D is drag force) exerted by wave and current. While wave generates F_M and part of F_D, current generates residual part of F_D. F is calculated by Morison's formula. Ocean current velocity u is broken down into steady flow velocity ν and fluctuating wave velocity ν_w cosωt (where, ν_w is half amplitude horizontal velocity of wave, angular velocity ω = 2π/T, T is wave period and t is time). Drag force F_D (= F^^-_D + F^^〜_D, where, F^^-_D is steady drag force and F^^〜_D is fluctuating drag force) has been calculated by Fourier transform. Conclusions are as follows: (1) Steady drag force F^^-_D acting on a structure, which is primarily generated by steady velocity ν, increases under the existence of fluctuating velocity ν_w cosωt. (2) Fluctuating drag force F^^〜_D acting on a structure which is primarily generated by ν_w, increases in the same frequency components as that of wave under the existence of steady velocity ν.
Nine artificial sea-mounts have already been constructed in rather shallow waters (i.e. less than 100 m). There is a strong demand for artificial sea-mounts in deeper waters to create a larger fertilized area for fishing. It is essential to construct an artificial sea-mount with the least number of blocks with the least scattering of blocks because the blocks tend to scatter during the drop, particularly with an increase in depth. The more the water depth increases, the more the blocks scatter on the ocean floor. It has been experimentally demonstrated through water tank experiments that scattering can be minimized by connecting four blocks loosely with rope or wire.
On the basis of the report published from Marine Accident Inquiry Agency, the operating state of the safety devices i.e. the alarm and automated shut-down device for engine system when the engine troubles arose was investigated. Results showed that the cases in which the engine broke down were 42 (25%), even though the safety devices operated, the cases in which the engine broke down were 67 (39%), since they did not operate. The breakdowns of the former causes in the engine troubles were artificial mistake, insufficient inspection, non-operation of engine shut-down device and the latter causes were insufficient maintenance, un-installation of the safety device, sensor fault. Therefore, the following matters are recommended from the viewpoint which prevents the engine troubles, 1) the execution of the operating test of the safety device, 2) the execution of the stop of the engine by the emergency stop button.
Engine performance before and after blower cleaning of turbocharger in main engine was measured in order to evaluate the fuel-saving effect of the detergent cleaning of the blower of the turbocharger. The results showed that there was almost no recognizable difference in the fuel consumption, the rotational frequency of turbocharger, and the maximum pressure of the cylinder for the engine power, however, the intake manifold pressure for the engine power increased and exhaust gas temperature for the engine power decreased. From these results, there was no fuel-saving effect on the blower cleaning of the turbocharger. However, the execution of that cleaning will contribute to the prevention of the accidents of cylinder-head, cylinder-liner, and exhaust valve.