Data from: Environmental influences and ontogenetic differences in vertical habitat utilisation of black marlin (Istiompax indica) in the Southwestern Pacific

The black marlin (Istiompax indica), is a highly migratory billfish that occupies waters throughout the tropical and sub-tropical Indo-Pacific. To characterise the vertical habitat use of I. indica, we examined the temperature-depth profiles collected using 102 pop-up satellite archival tags (PSATs) deployed off the east coast of Australia. Modelling of environmental variables revealed location, sea surface height deviation, mixed layer depth, and dissolved oxygen to all be significant predictors of vertical habitat use. Distinct differences in diel movements were observed between the size classes, with larger size classes of marlin (>50 kg) undertaking predictable bounce diving activity during day light hours, while diving behaviour of the smallest size class occurred randomly during both day and night. Overall, larger size classes of I. indica were found to utilise an increased thermal range and spend more time in waters below 150m, than fish of smaller size classes. The differences in the diving behaviour among size classes were suggested to reflect ontogenetic differences in foraging behaviour or physiology. The findings of this study demonstrate, for the first-time, ontogenetic differences in vertical habitat in a species of billfish, and further the understanding of pelagic fish ecophysiology in the presence of global environmental change.