A pop-up satellite tagging experiment was conducted to track the seasonal migratory pattern and range of the common thresher shark. On June 21-24, 1999, satellite tags were successfully deployed on eight large thresher sharks released in the Southern California Bight. These satellite tags can be pre-programmed to release from the fish at a specified time, pop up to the seas surface, and then beam their location and various other data to an orbiting satellite. The tags were pre-programmed to release 60, 120, 210 and 300 days after the release date.
As of March 23, 2000, five tags have successfully released from their host fish and transmitted location and archival temperature data to orbiting Argos satellite which has been subsequently downloaded. The first two tags popped up on schedule 2 months after tagging on August 20-21, 1999-- one released from a 246-cm TL male near the tagging location off Oceanside, CA, another from a 240-cm TL female 79 nm miles off Point Conception. Two months later on October 18, 1999, another tag released from a 260-cm TL male near Oceanside, while on October 20, a fourth released from 237-cm TL female 290 nm west of Magdalena, Baja California, Mexico. On January 18, 2000, a fifth tag released from a 255-cm female 540 nm southwest of La Paz, Mexico, approximately 160 miles west of Clarion Island.
These results confirm transboundary migration in this species and indicate a more offshore distribution than previously thought for the common thresher shark. This is the first deployment of satellite tags on a shark species, and the results are especially encouraging considering this species was once thought to be too large and delicate to land, tag, and release in good condition.