Vessel strikes have become a concerning source of mortality for sea turtles due to
increased turtle and vessel abundance in shared areas. For effective management strategies to be established, this threat to sea turtles must be thoroughly understood. To aid in this effort, we observed how green turtles (Chelonia mydas) reacted to oncoming vessels at varying speeds. We conducted observational boat surveys to measure turtle flight responses and flight initiation distances (distance from the bow of the vessel an animal begins flight behavior) and then compared behaviors of turtles of differing size classes (greater or less than 60 cm estimated carapace length). We found that green turtles’ average flight initiation distance was significantly driven by the speed of the oncoming vessel, with the average flight initiation distance reducing from a high of 7.7m in ideal conditions at 4 km to a high of only 5m in ideal conditions at higher speeds of 9 and 14 km . There was no correlation between flight initiation distance and the turtles’ size. Green turtles show a preference of flight behavior, fleeing directly away from the trajectory of the oncoming vessel in 51% of interactions (n = 78). Green turtle populations are rebounding, and the number of recreational vessels is increasing in coastal waters, meaning alikely increase in vessel/turtle interactions. This research looks to improve the available information on a threat for sea turtles in coastal waters and will be useful for managementorganizations to help reduce vessel related mortality.