Stable isotope analysis is an emerging tool to examine trophic pathways and migratory patterns of marine organisms. Squid are widely distributed in coastal and deep water regions of the Gulf of Mexico. Stable isotope ratios of carbon and nitrogen found within cephalopod tissues can provide information on both trophic level and habitat of their food sources. More recently, ontogenetic changes in stable isotope ratios within squid eye lenses have been documented. Concentric layers of crystallin proteins are added to the lens as the squid ages; the center of the lens contains the oldest layer and the youngest layers are on the outermost surface. The crystallin proteins are rich in carbon and nitrogen, providing suitable sources for isotopic analysis of both δ15N and δ13C. Doryteuthis plei is a common inshore squid in coastal waters of the western Atlantic region. This study identifies the geographic movements of D. plei in the eastern Gulf of Mexico using changes in isotope ratios in eye-lens layers. Isotopic analyses suggest that these squid begin their lives in the deep chlorophyll maximum of the outer shelf and move inshore as they age.