Comparison of growth patterns in three species of juvenile sea turtles

Sea turtles are most vulnerable to predators during early growth when they are small and
relatively defenseless. Predation risk might be reduced by evolving effective behavioral as well
as morphological defenses. Loggerhead Caretta caretta and green turtle Chelonia mydas neonates
hide in weed lines. They also become wider faster than they increase in length, a pattern of
positive allometry that may function to minimize the time during growth when they are
vulnerable to gape-limited predators. Virtually nothing is known about how young leatherbacks
grow which might reduce their vulnerability to predators. To find out, we reared 30 hatchlings
from 10 nests in the laboratory for up to 14 weeks, post-emergence. Once weekly, each turtle’s
body proportions straight line carapace length, SCL; straight line carapace width, SCW were
measured to yield an observed pattern of growth. That observed growth pattern was compared to
an expected pattern in which the turtles retained their hatchling proportions as they grew larger
isometric growth. We found that all of the leatherbacks showed allometric growth as their SCW
increased more rapidly than their SCL. Thus as they grew, leatherbacks became proportionally
wider, though this growth was not as pronounced as seen in loggerheads and green turtles. We
also modeled vulnerability to gape-limited predators. Leatherbacks, like loggerhead and green
turtles, were less vulnerable to predation when growing allometrically. These results provide
insight into a little know sea turtle life stage and aids in understanding how morphology in early
development may reduce predation risk.