Effect of ambient temperature on the vertical distribution and movement of Pacific bluefin tuna Thunnus thynnus orientalis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 206:251-260 (2000) - doi:10.3354/meps206251 Effect of ambient temperature on the vertical distribution and movement of Pacific bluefin tuna Thunnus thynnus orientalis Takashi Kitagawa1,*, Hideaki Nakata1, Shingo Kimura1, Tomoyuki Itoh2, Sachiko Tsuji2, Akira Nitta3 1Ocean Research Institute, University of Tokyo, Nakano, Tokyo 164-8639, Japan 2National Research Institute of Far Seas Fisheries, Fisheries Agency of Japan, Shimizu, Shizuoka 424-8633, Japan 3Japan NUS Co., Ltd, Minato, Tokyo 108-0022, Japan *E-mail: takashik@ori.u-tokyo.ac.jp ABSTRACT: Immature Pacific bluefin tuna Thunnus thynnus orientalis, marked with an archival tag, were released near Tsushima Island in the eastern East China Sea (58 individuals on 7 to 14 December 1995, 47 individuals on 29 November 1996). Of these, 15 were recovered by the following summer period. From the tags retrieved, we analyzed time-series data on swimming depth and ambient temperature recorded every 128 s. Our main objectives were to determine diurnal and seasonal changes in the swimming depth of bluefin tuna and examine the effect of ambient temperature on their vertical distribution and movement. In winter, the bluefin swam within the surface mixed layer at shallower depths during the night than during the day; swimming depth displayed diel periodicity. Some individuals displaying marked diel periodicity tended to migrate further offshore (direction southwest), where greater temperature gradients in the vertical water column were observed. This indicates that diel vertical migration of bluefin tuna is a direct response to changes in the thermocline. However, as the thermocline developed further in summer, the bluefin spent most of their time at the surface, suggesting that bluefin avoid rapid temperature change at the thermocline by making behavioral thermoregulation. During the summer, however, the fish made frequent dives through the thermocline during the day, and diel periodicity of swimming depth was more prominent than that in winter. The purpose of this movement is considered to be foraging. In conclusion, spatial and seasonal changes of the vertical structure of ambient water temperature have a great effect on the vertical distribution and movement of the bluefin tuna. KEY WORDS: Pacific bluefin tuna · Archival tag · Daily periodicity · Behavioral thermoregulation · Thermocline Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 206. Online publication date: November 03, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.