Vessel avoidance behavior in green turtles off the west coast of Florida

Vessel strikes are an increasing source of mortality for sea turtles in coastal waters with high recreational vessel traffic. We quantified flight initiation distance (FID) and avoidance behavior of green turtles Chelonia mydas in response to an approaching vessel traveling at different speeds in shallow coastal waters of Florida. Observational boat surveys were conducted at 3 vessel speeds, and observed FID was evaluated in relation to vessel speed, turtle size class (<60 cm vs. ≥60 cm estimated carapace length), and environmental conditions using a regression tree analysis. Observed FID was most strongly partitioned by vessel speed, with shorter mean distances consistently associated with higher speeds. Mean observed FID ranged from approximately 7.7 m at low vessel speed under specific environmental conditions to approximately 5 m or less at higher speeds. Turtle size class was not associated with differences in observed FID. Flight behavior was non-random, with turtles most frequently fleeing directly away from the vessel’s trajectory, and was independent of vessel speed and turtle size. Observed FID reflects the combined effects of turtle behavior and observer detection. Nevertheless, the consistent association between higher vessel speed and reduced observed FID supports management strategies that would reduce boat speeds and increase boater awareness to protect green turtles in shallow coastal habitats.