Vertical habitat use of sailfish (Istiophorus platypterus) in the Atlantic and eastern Pacific, derived from pop-up satellite archival tag data

Abstract

Vertical habitat use of sailfish (Istiophorus platypterus) was evaluated using pop-up satellite archival tag data from the eastern tropical Atlantic, western North Atlantic, and eastern tropical Pacific. Data included Argos transmitted depth, temperature, and light level frequency histograms binned at 1–8-h intervals, and four recovered pop-up satellite archival tags that provided high resolution archival data recorded at 30-s intervals. We tabulated the proportions of time spent within each degree of water temperature relative to the surface temperature (Delta T) and proportions of time at temperature, as these are major input variables for habitat standardization models used in stock assessment procedures. Frequency distributions were calculated for daylight, darkness, and twilight for each of the three regions and for all regions combined. Vertical habitat envelopes indicated greater use of deeper strata in the western North Atlantic, compared to the hypoxia-based habitat compressed regions of the eastern Atlantic and Pacific. However, there were no significant differences in Delta T distributions when comparing the three regions, affirming this metric for its application in habitat standardization models.