Radiocarbon and stable-isotope measurements in tooth growth layers helped scientists reconstruct parts of the lives of five whales stranded in Scotland. The 2026 study supports annual tooth-layer formation during early and middle life in some animals, but also shows why counting visible layers can underestimate the age of an older whale.
How can a whale’s tooth preserve its life history?
As a whale’s tooth grows, dentine is laid down in visible growth-layer groups. Scientists can sample those layers in sequence, from older material toward newer material, and look for chemical signatures preserved as the animal lived.
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The study examined dentine from two sperm whales (Physeter macrocephalus) and three killer whales (Orcinus orca), all stranded in Scotland. Researchers used two complementary kinds of evidence: radiocarbon to test the timing of tooth layers, and stable carbon and nitrogen isotopes to examine ecological changes over a whale’s life.
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Radiocarbon as a time marker
Mid-20th-century nuclear weapons tests added radiocarbon to the atmosphere, which then entered the oceans and marine food webs. This “bomb radiocarbon” produced a distinctive rise and decline over time. By comparing radiocarbon measurements from successive tooth layers with marine reference curves, researchers could assess when the layers formed and test whether layer groups represented annual growth.
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This historical weapons-test signal is different from the radiocarbon fingerprint associated with civilian nuclear reprocessing discharges at Sellafield, found in one whale in the study.
Stable isotopes as ecological clues
Carbon-13 and nitrogen-15 isotope values can help distinguish feeding histories and changes in marine ecology. They do not reveal an exact meal or identify prey species on their own. In this study, isotope profiles varied among individuals. The researchers interpreted higher nitrogen values in Lulu as pointing to a larger marine-mammal component in her diet, while lower values in two males suggested greater contributions from larger fish. These are clues, not proof of precisely what each whale ate.
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What did the radiocarbon results show about whale age?
Radiocarbon profiles in both sperm whales and one killer whale aligned with marine bomb-radiocarbon reference curves. That alignment supports annual growth-layer deposition during early and middle life in those animals. It does not establish that every layer forms annually throughout every whale’s life.
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One killer whale had 52 visible growth layers, but its radiocarbon chronology was consistent with an age of 65 years or more. For this individual, counting visible layers alone would have substantially underestimated age. The result suggests that layers can become compressed or less reliable as an age marker in older whales.
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Moby was at least 43 when he died
Moby, a sperm whale stranded in the Firth of Forth in 1997, was at least 43 years old at death, according to the University of Glasgow’s account of the study. His tooth offered a way to investigate the question lead author Kieran Tierney recalled asking: “Where had he come from? What sort of life had he had?”
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What did Lulu’s tooth reveal about Sellafield?
Lulu was a member of the West Coast Community of killer whales. Her tooth carried a distinct radiocarbon fingerprint associated with discharges from the Sellafield nuclear reprocessing facility. The researchers interpreted the signal as evidence that she foraged for a long time in the west of Scotland marine environment.
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This was a trace radiocarbon signature, not evidence that the sampled whales were dangerously radioactive. The study distinguishes the Sellafield-associated signal from the broader bomb-radiocarbon curve left by weapons testing.
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- Supported: In two sperm whales and one killer whale, radiocarbon evidence supported annual tooth-layer deposition during early and middle life.
- Not a universal age rule: The older killer whale’s 52 visible layers were consistent with an age of 65 or more, demonstrating that layer counts can fail to track age reliably in an individual.
- Useful ecological evidence: Carbon and nitrogen isotope patterns differed among the whales and helped researchers infer contrasting feeding histories.
- Not a detailed food diary: Isotope values alone cannot establish the exact prey species or meals eaten.
- Limited sample: The conclusions come from five whales, not a population-wide calibration for all killer whales, sperm whales, or other toothed whales.
As Tierney put it, “We’ve provided new evidence to show that tooth growth layers are deposited annually but this is perhaps only reliable up to a certain point in their lives.” The study’s value is in showing how chemical timelines can test tooth-layer counts and add context to the lives recorded in archived specimens, while leaving clear limits on what those records can prove.
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