Age-specific growth and maturity estimates for the flatback sea turtle (Natator depressus) by skeletochronology

Details

• Journal Title:
  PLoS ONE
• Personal Author:
  Turner Tomaszewicz, Calandra N. ; Avens, Larisa ; Seminoff, Jeffrey A. ; Limpus, Colin J. ; FitzSimmons, Nancy N. ; Guinea, Michael L. ; Pendoley, Kellie L. ; Whittock, Paul A. ; Vitenbergs, Anna ; Whiting, Scott D. ; Tucker, Anton D.
• NOAA Program & Office:
  NMFS (National Marine Fisheries Service) ; SEFSC (Southeast Fisheries Science Center) ; SWFSC (Southwest Fisheries Science Center)
• Description:
  To address a major knowledge gap for flatback sea turtles (Natator depressus), a species endemic to Australia and considered ‘Data Deficient’ for IUCN Red List assessment, we present the first-ever skeletochronology-derived age and growth rate estimates for this species. Using a rare collection of bone samples gathered from across northern Australia, we applied skeletochronology and characterized the length-at-age relationship, established baseline growth rates from the hatchling to adult life stages, and produced empirical estimates of age-at- and size-at-sexual-maturation (ASM, SSM). We analyzed humeri from 74 flatback sea turtles ranging in body size from 6.0–96.0 cm curved carapace length (CCL), and recovered from Western Australia (n = 48), Eastern Australia (n = 13), central Australia (n = 8; Northern Territory n = 3, the Gulf of Carpentaria n = 5), and unknown locations (n = 5). We identified the onset of sexual maturity for 29 turtles, based on rapprochement growth patterns in the bones. Estimates for ASM ranged from 12.0 to 23.0 years (mean: 16.3 ± 0.53 SE), SSM ranged from 76.1 to 94.0 cm CCL (mean: 84.9 ± 0.90 SE), and maximum observed reproductive longevity was 31 years for a 45-year old male flatback. Growth was modeled as a smoothing spline fit to the size-at-age relationship and at the mean SSM (84.9 cm CCL) corresponded with a spline-predicted maturity age of 18 years (95% CI: 16 to 24), while mean nesting sizes reported in the literature (86.4 to 94 cm CCL) corresponded to estimated ages of 24+ years. A bootstrapped von Bertalanffy growth model was also applied and showed consistencies with the spline curve, yielding an estimated upper size limit, Linf, at 89.2 ± 0.04 cm (95% CI: 85.5 to 95.9 cm) with the intrinsic growth rate parameter, k, at 0.185 ± 0.0004 (0.16 to 0.22); at the same mean SSM (84.9 cm CCL) the estimated ASM was 16.3 ± 0.05 years (95% CI: 12.8 to 27.7 years). Lastly, four of the samples analyzed were collected from deceased adult females that had previous sizes known from on-going mark/recapture studies at nesting sites in Western Australia. The paired CCL data (measured at nesting and back-calculated) did not significantly differ (p = 0.875). This first skeletochronology study for flatback sea turtles generates valuable empirical estimates for ongoing conservation and management efforts.
• Keywords:
  Growth Sea Turtles Sea Turtles
• Source:
  PLoS ONE 17(7): e0271048
• DOI:
  https://doi.org/10.1371/journal.pone.0271048
• Document Type:
  Journal Article
• Rights Information:
  CC BY
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha256:e84dac1b84233bba07b42edb5b0fd7aa5a9bf20f5e2dd1ecdb3b78cedfc7e927
• Download URL:
  https://repository.library.noaa.gov/view/noaa/45075/noaa_45075_DS1.pdf
• File Type:
  [PDF - 1.23 MB ]