I thank the captains and the crews of the Oshoro Maru and Hokusei
Maru for their assistance at sea and T. Takahashi, T. Nakatani,
and T. Takatsu for their help with sample collections and for their
encouragement and advice during the course of this work. I also
thank R. Ishida for teaching the otolith polishing technique and K.
Yabuki for providing unpublished growth data. Earlier draft of this
manuscript was improved through critical comments and useful
suggestions of two anonymous reviewers.