Fig. 2. Average distance (top) and

Fig. 2. Average distance (top) and movement rate (distance/interval, middle) between sequential calculated positions, and average error (bottom) by hour of the day for retained
positions of octopuses from semi-continuous tracking in a fixed array. An activity peak (vertical rectangle) was apparent between midnight and 0500 in average inter-ping dis-
tances and instantaneous movement rates of octopuses. The performance of the receiver array, as reflected in hourly average horizontal position error (HPE), which had no
peak, did not vary with time of day.