Sailfish (Istiophorus platypterus) Habitat Utilization in the Southern Gulf of Mexico and Florida Straits with Implications on Vulnerability to Shallow-Set Pelagic Longline Gear

A total of 19 pop-up satellite archival tags (PSATs) were deployed on sailfish in the southern Gulf of Mexico between 2005 and 2007 aboard a commercial pelagic longline vessel (n = 18) and a recreational rod-and-reel vessel (n = 1). All PSATs were programmed to collect pressure (depth), temperature, and light-level data for 10 days at approximately 90-second intervals. These point-level data were not summarized prior to transmission, allowing the reconstruction of vertical movement patterns. Three tags suggested mortality events and were excluded from subsequent analyses. We present the preliminary data analyses from the remaining 16 PSATs. Sailfish are primarily associated with the upper surface waters at 20 m or less depth. However, sailfish also exhibited numerous repeated short-duration vertical movements below the local thermocline to depths of 50-150 m. The depth utilization from these tagged fish coincide with the actively fished depths of shallow-set pelagic longline gear, yet appear to be shallower than the depths of settled deep-set gear used to target bigeye tuna.