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.

For species of conservation concern, somatic growth and age at maturation are key parameters in models used to evaluate population dynamics, as spatial and temporal variability in growth rates may be particularly important for predicting population recovery. Following an oceanic juvenile developmental stage, endangered Kemp’s ridley sea turtles Lepidochelys kempii occupy neritic habitats in 2 primary regions, the Gulf of Mexico (GoM) and along the US Atlantic coast. Results of prior studies suggest that somatic growth rates differ between these groups, which has the potential to influence maturation trajectories and relative reproductive contributions. To determine the nature and extent of potential regional differences, we conducted skeletal growth mark analysis (skeletochronology) with complementary annual bone growth increment-specific stable nitrogen isotope analysis that allowed delineation of oceanic-to-neritic habitat shifts for turtles stranded from 1993 to 2016. Results demonstrate that in the GoM, the oceanic-to-neritic habitat transition is associated with younger ages and faster somatic growth rates than in US Atlantic waters. Overall, US Atlantic somatic growth response was depressed relative to that in the GoM throughout all juvenile life stages, and this disparity persisted for more than 20 yr. This discrepancy translated into regional divergence in size-at-age relationships and maturation trajectories, with the prediction that US Atlantic Kemp’s ridleys would mature on average 2 to 3 yr later than their GoM counterparts. These analyses provide important baseline information on somatic growth rates and predicted age at maturation that can facilitate the evaluation of factors contributing to recent fluctuations in reproductive output for this endangered population.

No abstract