Abstract
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.
Highlights
The global distribution of the hawksbill sea turtle Eretmochelys imbricata is predominantly centered in tropical waters, its range in the westernNorth Atlantic extends into sub-tropical areas along the US Gulf of Mexico (GoM) and Atlantic coasts (Wallace et al 2010; Fig. 1)
Humeri were collected from 94 hawksbill sea turtles that stranded along the US coastline (Fig. 1) from 1989 through 2012, ranging in size from 7.5 to 80.8 cm straightline carapace length (SCL)
Through integration of multiple analytical approaches, we generated the first empirically derived estimates of juvenile hawksbill oceanic stage durations in the western North Atlantic, with turtles transitioning from oceanic to neritic habitats between the ages of ~1 and 3 yr and SCLs centered around 23−24 cm Predicted size
Summary
The global distribution of the hawksbill sea turtle Eretmochelys imbricata is predominantly centered in tropical waters, its range in the westernNorth Atlantic extends into sub-tropical areas along the US Gulf of Mexico (GoM) and Atlantic coasts (Wallace et al 2010; Fig. 1). In Florida, hawksbills regularly occur in nearshore waters off the southeastern coast, in the Florida Keys (including the Marquesas and Dry Tortugas) and in GoM waters off the west-central coast; they are rarely encountered along the upper northwest coast or in northeastern Florida (reviewed by Meylan & Redlow 2006). In-water survey, power plant entrapment, museum, cold-stunning, and incidental capture records in Florida have documented the regular presence of juvenile and, in some cases, adult-sized hawksbills
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