Sex-biased predation rates have been documented in marine turtles, but no study to date has addressed the causes of such bias. In Shark Bay, male Loggerhead Turtles (Caretta caretta) display evidence of Tiger Shark (Galeocerdo cuvier) attack more often than do females, and sex-specific differences in swim speed or maneuverability have been posited as a possible reason for this pattern. We used simulated shark attacks (boat chases) in shallow water to test this hypothesis. Differences in speed and maneuverability between males and females were not detected, indicating that the heightened vulnerability to predation of male Loggerhead Turtles in Shark Bay requires a different explanation.