Kara Dodge

Date of Award

Fall 2013

Project Type


Program or Major


Degree Name

Doctor of Philosophy

First Advisor

Maryellen M Lutcavage


The endangered leatherback turtle is a highly migratory predator that feeds exclusively on gelatinous zooplankton. Leatherbacks spend most of their lives submerged or offshore, and their at-sea biology (particularly that of males and sub-adults) is poorly understood throughout much of their range. I used satellite telemetry to monitor movements and dive behavior of nine adult and eleven sub-adult leatherbacks captured off Massachusetts, USA, and tracked throughout the NW Atlantic. Leatherback movements and environmental associations varied by oceanographic region, with slow, sinuous, area-restricted search behavior and shorter, shallower dives occurring in cool, productive, shallow shelf habitat at temperate latitudes. Leatherbacks were highly aggregated in temperate shelf waters during summer, early fall, and late spring, and more widely dispersed in subtropical and tropical habitat from late fall through early spring. Leatherbacks increased path sinuosity with decreasing water depth in temperate and tropical shelf habitats. This relationship is consistent with increasing gelatinous zooplankton biomass with decreasing depth, and bathymetry may be a key feature in identifying leatherback foraging habitat in neritic regions.

I used satellite-derived turtle tracks to examine migratory orientation cues of fifteen leatherbacks in the North Atlantic subtropical gyre. Individual leatherbacks were significantly oriented with no difference between adult and sub-adult headings, and turtles were significantly oriented with respect to magnetic field inclination, sunrise angle and sunset angle. Leatherbacks may use one or more of these features to orient during their open-ocean migrations between temperate and tropical latitudes.

I analyzed stable isotopes in leatherback tissues and prey to investigate feeding behavior. Leatherback skin and whole blood 813C values and red blood cell 815N values were correlated with body size, while 813C values of red blood cells, whole blood and blood plasma differed by sex. Mixing model results suggest that leatherbacks foraging off Massachusetts primarily consume. Cyanea capillata and Chrysaora quinquecirrha, and ctenophores, while a smaller proportion of their diet comes from holoplanktonic salps and sea butterflies (Cymbuliidae). My results are consistent with historical observations of leatherbacks feeding on scyphozoan prey in this region and offer new insight on sizeand sex-related differences in leatherback diet.