Fig. 1

Positioning of archival-tagged striped marlin (Fish 890271) using depth records. Clockwise from top left. a Light level data were properly sampled by sensor embedded in the external sensor stalk until the stalk was damaged less than two months post-release. Rise and fall in logged light levels corresponded to changes in ambient light throughout a 24-h day (y-axis, hours in UTC), with times of sunset and sunrise outlined in turquoise and purple, respectively. As soon as the sensor stalk was damaged, and eventually fell off, logged light level no longer reflected changes over the course of a day. b Depth data were still available many months after the external sensor stalk was damaged, as the pressure sensor was housed inside the main logger implanted in the fish’s body cavity. Diel swimming activities, including deeper during daytime and shallower at night, coupled with crepuscular ascents and descents have allowed an estimation of times of sunset (red line) and sunset (green line) in UTC. These solar events could then be used in the astronomical derivation of longitude and latitude estimates. c Track estimates obtained with logged light via Wildlife Computer’s GPE3 model (orange line), and with depth via our depth-based geolocation strategy (black line, crosses). Release (start) location is denoted by a green triangle, and tag recovery location by a red triangle. Note depth-logging terminated 626 days prior to physical tag recovery, which accounts for the apparently large discrepancy between the last track position and recovery location. d Final reconstructed track utilizing both light-based and depth-based positions