Dataset Submitted

Validating radiocarbon aging in sea turtle hatchling eye lenses

Authors: Jenna D. Bennett, Amy A. Wallace, William F. Patterson III, David J. Duffy, Hannah B. Vander Zanden
Identified On: Dec 20 2024 19:37 UTC
DOI: https://doi.org/10.7266/3t17a0wx
UDI: F3.x304.000:0001
Project Information

Funded By:
Florida RESTORE Act Centers of Excellence Program

Funding Cycle:
FLRACEP 3

Research Group:
Tissue Clocks: New Methods for Ageing and Decoding Sea Turtle Life Histories

Point of Contact

Hannah Vander Zanden
University of Florida
hvz@ufl.edu

Data Collection Period
1992-01-01
to
2021-12-31
Theme keywords

sea turtle, radiocarbon, stable isotopes, age

Abstract:

Population health assessments and conservation measures rely on accurate aging to estimate life-histories parameters, such as age at sexual maturity, timing of habitat shifts, and life-stage duration. Sea turtles are typically aged using skeletochronology, in which annual lines of arrested growth (LAGs) in the humerus are stained and counted, but there are multiple challenges to aging older individuals. In the 1950s and 1960s, nuclear weapons testing in the Pacific Ocean resulted in an atmospheric spike of radiocarbon (14C), which has become a useful tracer in aging applications of other taxa, including fish. In this study, we examined the efficacy of using eye lens Δ14C values to validate age estimates in sea turtle hatchlings. We measured loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtle eye lens Δ14C values from 15 hatchlings collected along eastern Florida during 2019-2021 and one hatchling from 1992. Hatchling sea turtle Δ14C values decreased annually, as expected. Though sea turtle eye lens Δ14C varied among individuals in a given year, this variation did not correlate with straight carapace length (SCL) or carbon and nitrogen stable isotope values.

Suggested Citation:

Jenna D. Bennett, Amy A. Wallace, William F. Patterson III, David J. Duffy, Hannah B. Vander Zanden. Validating radiocarbon aging in sea turtle hatchling eye lenses. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/3t17a0wx

Purpose:

The objective of this study was to examine the efficacy of using bomb 14C dating to validate sea turtle age estimates or to directly age sea turtles. This aim was accomplished by examining the correspondence between Δ14C values of known-age hatchling loggerhead and green turtles and the Gulf of Mexico and northern Caribbean Sea regional coral-otolith reference series.

Data Parameters and Units:

Turtle_ID: A unique identifier for each individual δ15N_skin: Nitrogen stable isotope values of hatchling skin (permil) δ13C_skin: Carbon stable isotope values of hatchling skin (permil) N_skin: Percent nitrogen content of hatchling skin (permil) C_skin: Percent carbon content of hatchling skin (permil) δ15N_lens: Nitrogen stable isotope values of hatchling lens (permil) δ13C_lens: Carbon stable isotope values of hatchling lens (permil) N_lens: Percent nitrogen content of hatchling lens (permil) C_lens: Percent carbon content of hatchling lens (permil) Lens_side: Side from which the lens was analyzed for radiocarbon Δ14C_whole: Radiocarbon values of entire hatchling lens (permil) Δ14C_core: Radiocarbon values of the hatchling lens core when it could be separated (permil) Δ14C_cortex: Radiocarbon values NOSAMS_no1: Lab identification number for National Ocean Sciences Accelerated Mass Spectrometry Lab for first sample analyzed from an individual NOSAMS_no2: Lab identification number for National Ocean Sciences Accelerated Mass Spectrometry Lab for second sample analyzed from an individual Washback_year: Year of collection Species: Scientific name Life_stage: H = hatchling based on straight carapace length (notch-to-notch) of < 50 mm, PH = posthatchling based on straight carapace length (notch-to-notch) >50 mm SCL_nt_mm: Straight carapace length, notch-to-tip (mm) SCL_nn_mm: Straight carapace length, notch-to-notch (mm) SCW: Straight carapace width (mm) Head_length_mm: Head length (mm) Head_width_mm: Head width (mm) Head_depth_mm: Head depth (mm) Lens_wet_wt_mg: Wet lens weight (mg) Lens_dry_wt_mg: Dry lens weight (mg)

Methods:

Loggerhead (Caretta caretta) and green (Chelonia mydas) turtle hatchlings were collected as part of a larger washback project conducted by the University of Florida’s Sea Turtle Hospital at the Whitney Laboratory for Marine Bioscience during the 2019-2021 nesting seasons. Washbacks were found ranging from Nassau to Volusia Counties, inclusive. One additional green turtle hatchling used in this study was collected at Melbourne Beach from an excavated nest and stored at the Archie Carr Center for Research University of Florida in 1992. Eye lenses were dissected, and subsamples were shipped to Woods Hole Oceanographic Institute National Ocean Sciences Accelerated Mass Spectrometry Lab (WHOI-NOSAMS) for Δ14C analysis. Methodological details are available at https://www2.whoi.edu/site/nosams/resources/methods/. Epidermis samples and second eye lenses were collected from hatchlings for δ13C and δ15N analysis to determine the possibility of any offsets due to dietary input. The δ13C and δ15N sample composition of eye lenses and epidermis samples was measured at the University of Florida’s Department of Geological Sciences.

Instruments:

Stable isotope values were measured on one of two instrumentation combinations: 1) a Carlo Erba NA 1500 CNS elemental analyzer (Thermo Scientific, Waltham, Massachusetts, USA) interfaced via a ConFlo II to a Delta V Advantage isotope ratio mass spectrometer (Thermo Electron, Waltham, Massachusetts, USA) or 2) an ECS 8020 elemental analyzer (NC Technologies, Milan, Italy) interfaced via a ConFlo IV interfaced to a Delta V Advantage isotope ratio mass spectrometer (Thermo Electron, Waltham, Massachusetts, USA).

Error Analysis:

Reference materials were used to calibrate stable isotope results. The standard deviation of USGS40 was 0.07 ‰ for δ13C values and 0.08 ‰ for δ15N values (n = 18 replicates), and the standard deviation of USGS41 was 0.20 ‰ for δ13C values and 0.13 ‰ for δ15N values (n = 8 replicates). Repeated measurements of a laboratory reference material, homogenized loggerhead scute, were used to examine consistency in a sample with similar isotopic and elemental composition to samples in this study. The standard deviation of the laboratory reference material was 0.06 ‰ for δ13C values and 0.15 ‰ for δ15N values (n = 4 replicates).