Potential impact of global warming on temperate tuna habitat

点击翻译按钮获取中文摘要

To clarify their vertical distribution of Pacific bluefin tuna (PBFT), Thunnus orientalis, and Dolphin fish (DF), Coryphaena hippurus, we obtained the data of swimming depth and temperature from data-loggers for PBFT in April, May and November 2007, and for DF in May, September and October 2007 in the East China Sea. With the developing vertical stratification in late May when sea surface temperature is over 20℃ in the northern part of the East China Sea, PBFT sifted the distribution from the surface to the bottom to just above the thermocline, although PBFT made vertical excursions to bottom layer in early May and November when vertical structure of water temperature was homogeneous. At the same time, DF which appeared in this area remained near the surface due to avoiding cooler water of <19 ℃. However, DF's data in September and October indicated that DF should extend the swimming depth in the surface mixed layer where longline hooks is set more, with rising temperature in the surface mixed layer and more intensify the thermal stratification. The change of their distributions in late spring will increase the chance that DF will encounter longline hooks. We suggest that for more efficient catch of the main target PBFT avoiding bycatch DF, the longlines should be set at the depth based on their vertical distributions related to their respective temperature preferences seasonal change of vertical temperature structure.