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 ve locities by swimming upstream for a greater proportion of the time. At temperatures of 21-25 degrees C currents equivalent to 1-2 body lengt hs 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 switc hed to synchronized forelimb flapping, with stationary rear limbs. Max imum dog-paddle speed was about 40% of maximum speed using synchronize d foreflippers: the latter mechanism is clearly capable of generating far more propulsive power. Maximum sustained swimming speeds at 25 deg rees C, 21 degrees C and 15 degrees C were 3.31, 2.96 and 2.09 body le ngths s(-1) respectively; the speed at 15 degrees C was significantly lower than at the other two temperatures, and could not be sustained f or more than 2-4 min before instability in pitch, roll and yaw prevent ed the animal from swimming upstream. A detailed analysis of the swimm ing mechanism at different temperatures is presented. This demonstrate d 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 o f vulnerability of the species to cold.