Speartooth Sharks May Live Longer Than Previously Thought, Study Suggests

Scientists have uncovered evidence that speartooth sharks (Glyphis glyphis), a critically endangered species, may live longer than previously estimated, according to a study published in Scientific Reports. The research, led by Hilary M.K. Lewis of the Australian National University and James Cook University, challenges traditional methods of aging sharks by using geochemical analysis of vertebrae, revealing that visible growth bands may not reliably indicate age.

How Do Scientists Estimate Shark Age?

For decades, researchers have estimated shark age by counting growth bands in vertebrae, similar to tree rings. These bands, visible under transmitted light microscopy (TLOM), were assumed to form annually. However, this method has proven inconsistent, especially in tropical species like the speartooth shark, where seasonal changes are less pronounced. “Different scientists can reach conflicting age estimates from the same vertebra,” said Lewis, whose team sought a more accurate approach.

Why This Study Matters for Conservation

The speartooth shark, found in northern Australian rivers, is listed as vulnerable by the IUCN, with fewer than 2,500 mature individuals remaining. Accurate age data is critical for conservation efforts, as it informs population recovery timelines and fisheries management. “If we misjudge how long sharks live or when they mature, we risk underestimating their vulnerability to overfishing,” Lewis explained.

New Techniques Reveal Hidden Age Clues

The study introduced geochemical methods to analyze strontium isotopes in shark vertebrae. By combining micro-XRF and laser ablation-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), researchers mapped elemental patterns linked to seasonal rainfall. During the wet season, increased strontium from weathered rocks created distinct isotopic signatures, aligning with annual wet-dry cycles. These chemical markers proved more reliable than visible bands, suggesting speartooth sharks may live beyond 11 years—longer than previously thought.

Implications for Shark Research and Policy

The findings raise questions about the accuracy of age estimates for other shark species. “Many long-lived marine animals rely on methods developed for temperate species,” Lewis noted. “This study highlights the need to adapt techniques to local environmental conditions.” The research also revealed that pregnant speartooth sharks likely stay in estuaries with higher marine influence, while pups are born during the wet season, a detail confirmed through elemental analysis.

What’s Next for Speartooth Shark Conservation?

Conservationists are now urging policymakers to update population models based on these findings. “This technique could be applied to other riverine sharks, but it requires funding and collaboration,” said Dr. Emma Johnston, a marine biologist at the University of Sydney. With speartooth sharks facing habitat degradation and fishing pressures, refining age estimation methods is a critical step toward protecting the species.