Use of Pop-Up Satellite Archival Tags to Determine Habitat utilization of sailfish (Istiophorus platypterus) in the Southern Gulf of Mexico.

To determine habitat utilization of sailfish in the southern Gulf of Mexico and Florida Straits, 18 pop-up satellite archival tags were deployed on animals incidentally captured during regular commercial pelagic longline fishing operations targeting swordfish and tunas. Tags were programmed for a 10-day deployment period, with point measurements of depth, temperature, and light level every 90 seconds. A total of 17 tags transmitted following the full deployment period, transmitting 25-82% of the archived data; three tags were also physically returned, allowing for 100% recovery of the archived data. The data recorded by the tags showed repeated short-duration movements throughout the deployment period to depths greater than 75 m for less than five minutes each, presumably for feeding. Diel differences in depth distributions and individual movement patterns are examined, including differences in habitat utilization in relation to the local mixed layer depth. The maximum depths of the short-duration movements are also well below the measured effective fishing depths of the common types of pelagic longline fishing gear used in this geographic area. The results suggest that recent efforts to reduce domestic fisheries interactions with sailfish by deploying pelagic longline fishing gear below the depths frequented by this species may be counterproductive and that other bycatch reduction methods should be explored.