Marine Turtle Demography Laboratory
Using bone growth layers to answer questions about the demography, habitat, and ecology of sea turtles.
The SWFSC Marine Turtle Demography Laboratory is a multi-user facility directed by Dr. Cali Turner Tomaszewicz. The lab utilizes analysis of growth layers in sea turtle bones to understand demography, habitat use and trophic ecology. Our facility houses a variety of equipment from an automated micro-drill sampler interfaced with 3D movement and microscope-equipped instant imaging software, to bone cross sectioning and preparation tools that aid in collecting samples from sea turtle bones. Below you will find more information and background on skeletochronology and associated analytical techniques.
Lab capabilities include bone extraction, cleaning, and drying, cross sectioning with low-speed Isomet saw and slicing with freezing stage microtome (in partnership with the Marine Mammal Stranding Lab), bone and tooth polishing, and automated micromilling of annual growth layers for stable isotope sample extraction (with applicability to other tissues including scutes, marine mammal teeth, fish otoliths, vertebrae and more.)
Skeletochronology is a means to date layers of growth within bones, akin to dendrochronology, the study of tree rings, or schlerochronology, more generally. Sea turtle humeri develop by adding annual layers on the outer edges of the bone, thereby creating a record through the building of internal rings. By identifying and measuring visible layers of arrested growth, representative of annual body growth, the Marine Turtle Ecology & Assessment Program researchers are able to learn a great deal from dead stranded turtles. This includes aging turtles, characterizing demographic patterns and age structure of populations in foraging areas, and estimating vital rates such as annual growth. It also allows for the recreation of multiple, sequential years’ worth of information on individual turtles, where each layer of arrested growth, is associated with an estimated age, body size, annual growth and calendar year. Further, using skeletochronology, together with sequential stable isotope analysis of annual growth layers (see below), we can determine the duration of turtles’ oceanic juvenile stage (the “lost years”), age-at-settlement to nearshore foraging areas, and residency time in specific habitats of interest, e.g., areas of high fishery interactions and bycatch.
Stable Isotope Analysis of Bone Growth Layers
Stable isotope analysis has many ecological applications and has become a common tool to answer diet and movement questions about many animals including marine turtles. These inferences are possible because the isotope compositions, or the chemistry, of a turtle’s body tissues are ultimately derived from its diet and location. As turtles shift diet, and or move from one habitat or ‘isoscape’ to another, they retain information from their previous diet and habitat. By sequentially sample a turtles’ humerus growth layers, we can reconstruct its history of diet and movement back in time. Coupled with skeletochronological analysis of adjacent humerus cross sections, isotopic analysis provides insights about the specific age, size, and year at which a turtle moved between two isotopically distinct habitats (i.e. oceanic to neritic habitat). These data are crucial for determining the residency times for sea turtles in different marine regions and for understanding the susceptibility of sea turtles to spatially explicit threats such as fisheries related bycatch.
The combination of these two techniques, developed by the Marine Turtle Ecology & Assessment Program researchers, has been applied to sea turtle populations around the world.
Turner Tomaszewicz, C, Seminoff JA, Peckham H, Avens L, Goshe L, Rguez-Baron JM, Kurle CM (2018) Expanding the coastal forager paradigm: Long-term pelagic habitat use by green turtles (Chelonia mydas) in the eastern Pacific Ocean. Marine Ecology Progress Series. doi.org/10.3354/meps12372
Turner Tomaszewicz C, Seminoff JA, Kurle CM (2017) Stable isotope discrimination factors and between-tissue isotope comparisons for bone and skin from captive and wild green sea turtles (Chelonia mydas). Rapid Communications in Mass Spectrometry. https://doi.org/10.1002/rcm.7974
Turner Tomaszewicz C, Seminoff JA, Peckham SH, Avens L, Kurle CM (2017) Intrapopulation variability in the timing of ontogenetic habitat shifts in sea turtles revealed using δ15N values from bone growth rings. Journal of Animal Ecology, doi:10.1111/1365-2656.12618.
Turner Tomaszewicz C, Seminoff JA, Avens L, Kurle CM (2016) Methods for sampling sequential annual bone growth layers for stable isotope analysis. Methods in Ecology and Evolution 7:556-564.
Turner Tomaszewicz C, Seminoff JA, Ramirez M, Kurle CM (2015) Effects of demineralization on the stable isotope analysis of bone samples. Rapid Communications in Mass Spectrometry 29:1879-1888.
Turner Tomaszewicz C, Seminoff JA, Peckham SH, Avens L, Goshe L, Bickerman K, Rodriguez-Baron JM, Kurle CM (2015) Age and residency duration of loggerhead turtles at a North Pacific bycatch hotspot using skeletochronology. Biological Conservation 186:134-142.
Conrad, C., L. Pagès, J.A. Seminoff, C. Turner Tomaszewicz, M. Stoyka, E.L. Jones, K.
Bruner, and A.G. Pastron. In Press. Stable Isotope Ecology and Ancient DNA Analysis of Sea Turtles (Cheloniidae) from the Gold Rush-era (1850s) Eastern Pacific Ocean. Open Quaternary.