Scientists use lasers to reveal the hidden age of sharks

Scientists have discovered a flaw in the long-used method of aging sharks by counting vertebrae bands, particularly for the critically endangered speartooth shark (*Glyphis glyphis*). This rare species inhabits murky rivers and estuaries in northern Australia and Papua New Guinea, with fewer than 2,500 adults remaining. Traditional band-counting methods, which assume each light-dark pair represents a year, often misread tropical water patterns, especially in older sharks where bands compress. The new study instead analyzed strontium isotopes in shark vertebrae using lasers and X-rays. Strontium from seawater and freshwater leaves distinct chemical signatures in bone layers, creating a reliable yearly record tied to seasonal rainfall. Researchers matched these chemical patterns to real weather data from the Adelaide River system, confirming each wet and dry season left a distinct mark. This method provided a precise timeline of the shark’s life, unlike the ambiguous visual bands. When compared, the chemical age estimates often differed from band-counting results, with bands frequently misaligned or undercounted. This discrepancy suggests prior age estimates for speartooth sharks—and potentially other tropical species—may be inaccurate. Given their slow growth and late reproduction, even small errors in age estimates can lead to flawed conservation strategies, including incorrect fishing limits or recovery timelines. The findings highlight the need for alternative aging techniques in tropical regions, where seasonal changes are less pronounced. Strontium chemistry offers a promising solution, as it captures environmental conditions year by year. For speartooth sharks, this could mean more precise population assessments and better protection for one of the ocean’s most vulnerable species. The study underscores how advances in technology can reshape wildlife conservation. By leveraging chemical analysis, scientists may now uncover hidden truths about shark lifespans, directly impacting efforts to save them from overfishing and habitat loss. The research also raises questions about age estimates for other tropical shark species, where traditional methods may similarly fall short.