The temperature–depth structure the opah encounters is estimated from a temporal interpolation using the eight pairs of temperature and depth values from each 4-h period over the duration of the tag deployment (Fig.  7 ) Overlaid on this vertical structure is the mean daily opah depth (Fig.  7 ).

The mean daily depth of this opah was about 200 m until about October 21 when it suddenly shifted to about 150 m for most of the remaining record (Fig.  7 ).

The shift in mean depth occurred when there was a shoaling of the temperature–depth structure and it appeared the opah moved shallower in response to a shoaling of the temperature–depth structure (Fig.  7 ).

After about 5 days with a mean depth of about 125 m the opah appeared to have moved into a region with a deeper temperature–depth structure (the edge of the eddy) and its mean daily depth increased to 225 m (Fig.  7 ).

About a week later, the temperature–depth structure shoaled somewhat and the opah moved shallower (Fig.  7 ).

Thus, in both opah, their mean daily depths moved deeper or shallower coherent with changes in the temperature–depth structure (Fig.  7 ).