Fig. 4

Characteristic changes in PSAT tilt and depth during swimming bouts for Port Frederick fish. A 15-min segment of a detailed data set from a wild Pacific halibut (Hippoglossus stenolepis), fish PF-3, tagged with an accelerometer Pop-up Satellite Archival Tags in Port Frederick (PF), Alaska provides an example of typical PSAT tilt patterns (a) during swimming bouts (grey rectangles) that coincide precisely with changes in depth (b). The tag is in a vertical position at a value of − 1 g while the fish is stationary but abruptly switches to a more horizontal orientation and tilt values exceed the threshold of − 0.75 g (horizontal dashed line) that classifies movement as active in the %tilt PSAT algorithm. The knockdown (KD) algorithm (vertical dashed line) detects the change from vertical (inactive) to more horizontal (active) tilt values when movement bouts are initiated (here, n = 7 KDs)