Vertical and horizontal movements of sailfish (Istiophorus platypterus) near Taiwan determined using pop-up satellite tags

Sailfish (Istiophorus platypterus) are of substantial economic importance to Taiwan because of their seasonal abundance (April to October, with a peak from May to July) off the island's eastern coast. They are harvested by drift gill nets, set nets, harpoons, and as incidental bycatch by inshore longline fisheries. Although the biology of sailfish has been investigated in eastern Taiwan, there is a paucity of data on movement patterns. Pop-up satellite archival tags (PSATs) were used to study the vertical and horizontal movements of three sailfish in 2008. The fish were tagged near the southeastern coast of Taiwan and linear displacements ranged from 1050 to 1400 km (~ 40 km day− 1) from deployment to pop-up locations and all movements were confined to the East China Sea. Sailfish spent 88% of their time in the upper uniform mixed layer above 50 m, but made more extensive vertical movements during the nighttime (x¯ = 60.61 m ± 48.24 SD) than daytime (x¯ = 35.21 m ± 35.37 SD). Depths and ambient water temperatures visited ranged from 0 to 214 m and 30.0° to 17.8 °C, respectively. However in all cases, the depth distribution appeared primarily limited by an 8 °C change in water temperature. Diel diving patterns also suggested basking behavior. Sailfish behavior makes them particularly vulnerable to surface fishing gears.

Research Highlights
► Pop-up satellite archival tags were used to study movements of sailfish in Taiwan.
► Sailfish spent 88% of their time in the upper uniform mixed layer above 50 m.
► Depth distribution appears to be limited by an 8 °C change in water temperature.
► Diving patterns suggested daytime basking with more varied movements at nighttime.
► Diving behavior makes sailfish vulnerable to surface fishing gears.