Aquatic Turning Performance in Juvenile Loggerhead and Green Sea Turtles.

Abstract

Sea turtles are known for being accomplished swimmers, capable of covering great distances. Despite the importance of maneuverability, little has been done to define the mechanics of turning in these marine organisms. To examine turning performance, juvenile loggerhead (Caretta caretta) and green sea turtles (Chelonia mydas) were video recorded overhead in pursuit of food in a large tank. The turtles were observed performing two types of yawing turns: pure rotational turns and translational turns. The trajectory of points on the body of the turtles (rostrum, anterior of shell, and posterior of the shell) were digitally tracked. X and Y coordinates were analyzed over time with a custom MatLab code, which estimated center of mass (COM), turn radius, and turn rate (angular velocity). Turning performance significantly differed between sea turtle species during rotational turns but did not significantly differ between sea turtle species during translational turns. Asymmetries were observed in limb usage during turns, which affected the angular velocity. Stroke frequencies significantly differ between turn type, but not between species. Analysis of the coordination of flippers suggests that C. caretta more often initiates turns with both forelimbs, while C. mydas more often initiates turns with one forelimb. When mapped categorically with other swimming taxa, sea turtles, resembled most other rigid-bodied swimmers, and placed below the guideline separating flexible-bodied swimmers and rigid-bodied swimmers. These data support the hypothesis that having a rigid body-plan constrains turning performance.