The effects of current velocity and temperature upon swimming in juvenile green turtles Chelonia mydas L.

Young green turtles, Chelonia mydas responded to increasing current velocities by swimming upstream for a greater proportion of the time. At temperatures of 21-25 degrees C currents equivalent to 1-2 body lengths s(-1) induced continuous upstream swimming. At low current velocity the turtles usually employed 'dog-paddle' (ipsilateral synchronized:) swimming. At swimming speeds of 0.8-1.4 body lengths s(-1) they switched to synchronized forelimb flapping, with stationary rear limbs. Maximum dog-paddle speed was about 40% of maximum speed using synchronized foreflippers: the latter mechanism is clearly capable of generating far more propulsive power. Maximum sustained swimming speeds at 25 degrees C, 21 degrees C and 15 degrees C were 3.31, 2.96 and 2.09 body lengths s(-1) respectively; the speed at 15 degrees C was significantly lower than at the other two temperatures, and could not be sustained for more than 2-4 min before instability in pitch, roll and yaw prevented the animal from swimming upstream. A detailed analysis of the swimming mechanism at different temperatures is presented. This demonstrated a significant degradation of co-ordination of swimming at 15 degrees C, even though the lethal temperature of green turtles is well below 10 degrees C. The significance of this finding is discussed in terms of vulnerability of the species to cold.