The isotopic composition of tooth-bound collagen has long been used to reconstruct dietary patterns of animals in extant and paleoecological systems. For sharks that replace teeth rapidly in a conveyor-like system, stable isotopes of tooth collagen (δ¹³C_tooth & δ¹⁵N_tooth) are poorly understood and lacking in ecological context relative to other non-lethally sampled tissues. This tissue holds promise, because shark jaws may preserve isotopic chronologies from which to infer individual-level ecological patterns across a range of temporal resolutions.  

Carbon and nitrogen stable isotope values were measured and compared between extracted tooth collagen and four other, non-lethally sampled tissues of varying isotopic turnover rates: blood plasma, red blood cells, fin, and muscle, from eight species of sharks. Individual-level isotopic variability of shark tooth collagen was evaluated by profiling teeth of different ages across whole jaws for the shortfin mako shark Isurus oxyrinchus and sandbar shark Carcharhinus plumbeus.

Measurements of δ¹³C_tooth and δ¹⁵N_tooth were positively correlated with isotopic values from the four other tissues. Collagen δ¹³C was consistently ¹³C-enriched relative to all other tissues. Patterns for δ¹⁵N were slightly less uniform; tooth collagen was generally ¹⁵N-enriched relative to muscle and red blood cells, but congruent with fin and blood plasma (values clustered around a 1:1 relationship). 

Significant within-individual isotopic variability was observed across whole shortfin mako shark (δ¹³C range = 3.5‰, δ¹⁵N range = 3.8‰) and sandbar shark (δ¹³C range = 2.4‰ -5.4‰, δ¹⁵N range = 2.4‰ – 5.8‰) jaws, which trended with tooth age. 

We conclude that tissue amino acid composition and associated patterns of isotopic fractionation result in predictable isotopic offsets between tissues. Future measurements will refine the use of this tissue as an ecological and paleoecological proxy. Within-individual variability of tooth stable isotope values suggests teeth of different ages may serve as ecological chronologies, which could be applied to studies on migration and individual-level diet variation across diverse time scales. Improvements in understanding tooth replacement rates, isotopic turnover, and associated fractionation of tooth collagen will enhance inferences that can be made from the isotopic composition of shark tooth, outlining clear goals for future scientific inquiry.  

See published article for information on sample collection, processing, and stable isotope measurements.