颱風對小型圓框沉下式箱網之結構與深度之影響

       國內外常有颱風侵襲箱網養殖場並造成養殖魚類全死亡或逃逸，造成養殖業者莫大損失之事件。臺灣夏秋期間經常有颱風來襲，部分箱網養殖業者採用圓框沉下式箱網 (submersible cage)，使整組箱網沉入離海表面約20 m 水深處避開海面強流與強浪，但卻無法得知箱網於水下的變化情形。本研究以實際箱網養殖場之小型圓框沉下式箱網 (網框直徑16 m、網深8 m)，結附9個水深計於箱網四周測點上，並設置1組流速流向儀，藉以觀測颱風前後箱網於水下的深度變化與養殖海域之流向與流速。無颱風時，箱網於水下各測點均能保持穩定深度，養殖海域海流流速超過20 cm/s時，易使網具上浮，造成容積比減少。莫蘭蒂颱風中心通過養殖海域時，海流流速超過30 cm/s且持續約3 hr，最高流速可達41.6 cm/s，且維持約半小時；箱網由水深 20 m處上浮至 5–8 m，且箱網發生嚴重變形。馬勒卡颱風中心未經過養殖海域，但亦造成箱網上浮，且網片嚴重變形，使得養殖空間遭壓縮變小。本研究成果可提供箱網養殖產業在開發抗強流箱網及提升水下固定網形與水下錨碇技術的參考依據，並探索減少下沉箱網網具變形的方法，降低養殖魚類的死亡率。

       Frequent occurrences of typhoons invading cage culture farms and causing the death or escape of all the farming fish result in substantial losses for farmers in our country and abroad. Before a typhoon hits Taiwan, fishermen who use round submersible cage farming will submerge the cage to a depth of about 20 meters to avoid the effects of strong currents and waves on the sea surface. Typhoons are prevalent in Taiwan during the summer and fall. However, the fisherman are unaware of the depth changes of the cage. In this study, 9 depth sensors and an Acoustic Doppler Current Profiler were attached to a small round submersible cage with a diameter of 16 m and a net depth of 8 m in order to detect the change in the cage's depth in different parts, as well as the speed and direction of current during the typhoon that struck Taiwan. The cage can maintain a stable depth when there is no typhoon, but when the current speed exceeds 20 cm/s, its volume ratio will decrease and it will float to the surface. When the center of the Meranti Typhoon passes through the culture farm, the current speed exceeds 30 cm/s for approximately three hours, with a maximum speed of 41.6 cm/s that is maintained for approximately half an hour. The deformed cage is floated from a depth of 20 meters to a depth of 5 to 8 meters. The center of the Malakas Typhoon did not pass through the culture farm, but it caused the cage to float upwards and the mesh to become severely deformed, resulting in a reduction in breeding space. This research may provide the cage culture industry with references for the technological development of the anti-strong flow cage, cage structure fixation, and underwater anchor to reduce fish culture mortality.