Sea turtles -- Mortality

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.

Two species of sea turtle, loggerheads (Caretta caretta) and leatherbacks (Dermochelys
coriacea) are caught frequently as bycatch in longline fisheries. These fisheries use
hooks baited with fish or squid. Yet, leatherbacks feed on gelatinous prey while
loggerheads are carnivores. I investigated the responses of these two species to bait
odors in controlled laboratory experiments to better understand their feeding behavior
and why they interact with longlines. Both species initiated feeding behavior in the
presence of squid bait odors and just C. caretta showed feeding behavior with sardine
odors; neither responded to mackerel odors. The turtles are hooked differently on
longlines. Loggerheads are usually hooked in the mouth while leatherbacks are usually
hooked in the shoulder or flippers. Comparisons of prey attack behavior and accuracy in
apprehending a stimulus in the presence of waterborne food odors identified speciesspecific differences that may predispose the turtles to particular kinds of hooking.