title: Time in tortoiseshell: a bomb radiocarbon-validated chronology in sea turtle scutes.
abstract: Some of the most basic questions of sea turtle life history are also the most elusive. Many uncertainties surround lifespan, growth rates, maturity and spatial structure, yet these are critical factors in assessing population status. Here we examine the keratinized hard tissues of the hawksbill (Eretmochelys imbricata) carapace and use bomb radiocarbon dating to estimate growth and maturity. Scutes have an established dietary record, yet the large keratin deposits of hawksbills evoke a reliable chronology. We sectioned, polished and imaged posterior marginal scutes from 36 individual hawksbills representing all life stages, several Pacific populations and spanning eight decades. We counted the apparent growth lines, microsampled along growth contours and calibrated Δ(14)C values to reference coral series. We fit von Bertalanffy growth function (VBGF) models to the results, producing a range of age estimates for each turtle. We find Hawaii hawksbills deposit eight growth lines annually (range 5-14), with model ensembles producing a somatic growth parameter (k) of 0.13 (range 0.1-0.2) and first breeding at 29 years (range 23-36). Recent bomb radiocarbon values also suggest declining trophic status. Together, our results may reflect long-term changes in the benthic community structure of Hawaii reefs, and possibly shed light on the critical population status for Hawaii hawksbills.
authors.affiliation: NOAA Fisheries, Pacific Islands Fisheries Science Center, 1845 Wasp Boulevard, Building 176, Honolulu, HI 96818, USA Nicholas School of the Environment, Duke University, 450 Research Drive, Durham, NC 27708, USA kyle.vanhoutan@gmail.com.
authors.forename: Kyle S
authors.initials: KS
authors.lastname: Van Houtan
authors.affiliation: NOAA Fisheries, Pacific Islands Fisheries Science Center, 1845 Wasp Boulevard, Building 176, Honolulu, HI 96818, USA.
authors.forename: Allen H
authors.initials: AH
authors.lastname: Andrews
authors.affiliation: NOAA Fisheries, Pacific Islands Fisheries Science Center, 1845 Wasp Boulevard, Building 176, Honolulu, HI 96818, USA.
authors.forename: T Todd
authors.initials: TT
authors.lastname: Jones
authors.affiliation: NOAA Fisheries, Pacific Islands Fisheries Science Center, 1845 Wasp Boulevard, Building 176, Honolulu, HI 96818, USA.
authors.forename: Shawn K K
authors.initials: SK
authors.lastname: Murakawa
authors.affiliation: Vertebrate Zoology Collections, Bernice Pauahi Bishop Museum, 1525 Bernice Street, Honolulu, HI 96817, USA.
authors.forename: Molly E
authors.initials: ME
authors.lastname: Hagemann
mesh_terms: D060105:Animal Shells / Q000737:chemistry*; D000818:Animals; D044822:Biodiversity; D054042:Bombs; D057894:Coral Reefs; D006254:Hawaii; D055110:Radiometric Dating; D013997:Time Factors; D014426:Turtles / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*
keywords: Eretmochelys imbricata; age determination; carbon-14; coral reefs; maturity; somatic growth