Takashi Kitagawa and Ko Fujioka

Session 3, Talk 2, 18/1/16 @ 1530 hrs

Investigations of the migration and distribution of Pacific bluefin tuna (PBT) in the Pacific Ocean have used fisheries data analysis and/or conventional tagging experiments mainly in the 20^th century, but these previous studies could not follow the detailed behavior of individuals at a higher resolution. The electronic tags that were developed and applied to fish species at the end of the last century allowed the measurement of environmental and physiological variables by recording raw or processed data in their memory. The tags used for PBT research allow a rough estimation of fish geolocation using a light sensor. To date, more than 800 PBT tuna tagged with the electronic tags have been released in the western Pacific Ocean (WPO). Analyses of the retrieved tag data have shown that the vertical distributions and movements of immature PBT are affected by spatial and seasonal changes in the vertical temperature structure. They make brief dives to depths below the thermocline for foraging and maintaining body temperature. The data indicate they aggregate in the Kuroshio-Oyashio transition region where they spent much more time at the surface feeding than in the other areas in the WPO. The timing of their trans-Pacific migrations from the transition region to the Eastern Pacific appears to depend on their wintering areas. We also suggest directions of future research for investigating PBT migratory characteristics in the WPO.

Contact:  T. Kitagawa, Atmosphere and Ocean Research Institute, University of Tokyo, Japan, This email address is being protected from spambots. You need JavaScript enabled to view it.