Pate, Jessica Hope

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.

Marine turtles produce many offspring which offsets the high mortality
experienced by turtles during early development. Juvenile mortality might be reduced by
evolving effective behavioral as well as morphological anti-predator defenses. Body
proportions of three species (Caretta caretta, Chelonia mydas, Dermochelys coriacea) of
turtles were measured in the first fourteen weeks of development to examine how growth
may mitigate predation by gape-limited predators. Growth was categorized as isometric
if shape did not change during development or allometric if body shape did change. All
three species showed allometric growth in carapace width; however it was less
pronounced in the larger D. coriacea turtles. Allometric growth in carapace width
decreased as all three species grew in size. When high predation occurs in early
development, many species will favor rapid growth into a size refuge. Juvenile sea turtles
may optimize their survival by growing allometrically when predation risk is the greatest.