Effective management of a rapidly increasing juvenile green sea turtle Chelonia mydas population necessitates an understanding of the foraging grounds utilized throughout ontogeny. We used stomach content (SCA) and stable isotope analyses (SIA) of multiple size classes of green turtles foraging along the middle (MTC) and lower Texas coasts (LTC) in the northwestern Gulf of Mexico to identify ontogenetic shifts in foraging behavior. Spatial differences in diet and habitat residency were examined based on samples gathered from live (n = 55) and deceased turtles (n = 114). Additionally, the isotopic composition of putative forage material within nearshore and inshore habitats was investigated to determine prey contribution to diet. Green turtle recruitment to neritic channel environments in Texas waters at sizes < 25 cm straight carapace length (SCL) was established based on the presence of benthic macroalgae in the diet. Integration of SCA with SIA of carbon and nitrogen in scute material, as well as potential prey, revealed a subsequent inshore shift to seagrass beds before obtaining 35 cm SCL for turtles of the LTC, while turtles from the MTC exhibited considerable variation in size at transition. This study improves our understanding of the feeding ecology of green turtles within critical foraging grounds along the Texas coast. KEY WORDS: Green turtle • Chelonia mydas • Ontogenetic shift • Stomach content analysis • Stable isotope analysis • δ 13 C • δ 15 N • Gulf of Mexico • Texas Resale or republication not permitted without written consent of the publisher

Oceanic dispersal characterizes the early juvenile life‐stages of numerous marine species of conservation concern. This early stage may be a ‘critical period’ for many species, playing an overriding role in population dynamics. Often, relatively little information is available on their distribution during this period, limiting the effectiveness of efforts to understand environmental and anthropogenic impacts on these species. Here we present a simple model to predict annual variation in the distribution and abundance of oceanic‐stage juvenile sea turtles based on species’ reproductive output, movement and mortality. We simulated dispersal of 25 cohorts (1993–2017) of oceanic‐stage juveniles by tracking the movements of virtual hatchling sea turtles released in a hindcast ocean circulation model. We then used estimates of annual hatchling production from Kemp's ridley Lepidochelys kempii (n = 3), green Chelonia mydas (n = 8) and loggerhead Caretta caretta (n = 5) nesting areas in the northwestern Atlantic (inclusive of the Gulf of Mexico, Caribbean Sea and eastern seaboard of the U.S.) and their stage‐specific mortality rates to weight dispersal predictions. The model's predictions indicate spatial heterogeneity in turtle distribution across their marine range, identify locations of increasing turtle abundance (notably along the U.S. coast), and provide valuable context for temporal variation in the stranding of young sea turtles across the Gulf of Mexico. Further effort to collect demographic, distribution and behavioral data that refine, complement and extend the utility of this modeling approach for sea turtles and other dispersive marine taxa is warranted. Finally, generating these spatially‐explicit predictions of turtle abundance required extensive international collaboration among scientists; our findings indicate that continued conservation of these sea turtle populations and the management of the numerous anthropogenic activities that operate in the northwestern Atlantic Ocean will require similar international coordination.

Sea turtles exhibit complex life histories, encompassing intermittent use of multiple spatially separated habitats throughout long lifespans. This broad scope presents challenges for collecting comprehensive biological and ecological data, yet absence of such information complicates evaluation of management strategies for populations at risk of extinction. Hawksbill sea turtles Eretmochelys imbricata are endangered worldwide, primarily due to long-term, directed harvest. However, available information regarding life stage durations, somatic growth patterns, and maturation attributes to enhance understanding of anthropogenic impacts and recovery potential remains constrained. To address these data gaps in the western North Atlantic, we conducted skeletochronological analysis for hawksbills stranded along US coastlines to generate straight-line carapace length (SCL)-at-age and somatic growth data. Generalized additive mixed models and bootstrapped von Bertalanffy growth curves were used to characterize age at maturation and covariate influence on somatic growth. For a subset of turtles, annual bone growth increment-specific stable isotope and trace element analyses were incorporated to evaluate habitat use relative to age. Integration of these data sources indicated that juveniles transitioned from oceanic to neritic habitat at 1-3 yr old and mean SCLs of 23-24 cm (range 15.7-35.0 cm). Initial ages at maturation for this population at minimum nesting female SCLs were estimated at 15-25 yr. Somatic growth varied significantly relative to size, age, and stranding location, while no association with sex or calendar year was observed. Our results demonstrate the utility of these complementary analytical approaches for generating baseline data fundamental to characterizing hawksbill sea turtle population attributes.

Knowledge of green turtle (Chelonia mydas) foraging ecology in the northwestern Gulf of Mexico (GOM) is critical as populations begin to recover from heavy harvesting in prior centuries. We present a comprehensive long-term assessment of green turtle diets from carcasses salvaged from 1987 to 2014 along the Texas coast. Digestive tract contents were examined from 420 green turtles, ranging in size from 7.3 to 86.0 cm in straight carapace length (SCLmax). Green turtles as small as 16.2 cm SCLmax recruit from the oceanic environment to nearshore foraging habitat in the northwestern GOM and consume macroalgae principally. A successive shift in diet and habitat to inshore seagrasses was evident by the seagrass-dominated diet of turtles larger than 30 cm SCLmax. Animal matter remained a frequently ingested diet item suggesting these immature green turtles are better classified as omnivores. The overall evidence indicates that Texas’ recovering green turtle assemblage is exhibiting foraging plasticity within seagrass meadows changing species composition and density.