We tagged 84 bluefin tuna with electronic pop-up tags and released them in the Mediterranean and the Strait of Gibraltar between June 1998 and August 2000; 25 (32 percent) were located by the Argos satellite system. Location rates were 21 and 62 percent, respectively, for single-point tags (61 released) and archival tags (23 released). Most tags surfaced in the western Mediterranean and eastern Atlantic, but one archival tag transmitted from a position south of Iceland and one single-point tag transmitted from the Greenland Sea. No transatlantic migrations were observed. Most tags released in the western Mediterranean surfaced near the tagging location, suggesting local residency. Residency and spawning site fidelity (which was also indicated by our data), offer the potential for overexploitation, if the industry progressively catches more large tuna for fattening. Domestication needs to obviate this risk. PAT tag experiments were conducted in collaboration with the Tuna Research and Conservation Center, USA.