Chemical clues from old shark jaws reveal diets and habitats

Sharks have roamed the oceans for millions of years. Their powerful jaws and sharp teeth make them top predators that are capable of influencing entire marine ecosystems.

However, understanding what they eat and where they feed remains difficult. This is especially true for rare or protected species where direct sampling poses legal and ethical challenges.

Traditionally, scientists study shark diets by examining their teeth. But collecting samples from live sharks can be risky, costly, and often impossible, especially when dealing with threatened species.

Yet, every opportunity to gather data matters. That’s where the past meets the present – inside the drawers and display cases of museums.

A new study led by researchers from Flinders University has found that preserved shark jaws – often considered to be static relics – can be a powerful scientific resource.

Using teeth from sharks in historical collections, researchers can now study shark diets without touching a living specimen.

This breakthrough offers new hope for marine science and conservation.

Shark jaws reveal feeding secrets

Shark teeth hold chemical signatures that reveal details of their past meals and feeding grounds. These signatures come from ratios of stable isotopes – naturally occurring variations of chemical elements. By examining these isotopes, scientists can piece together an animal’s ecological history.

Until now, scientists avoided using preserved jaws due to concerns that cleaning chemicals might have distorted the isotopes.

Many shark jaws in museums and private collections have been treated with substances like ethanol, bleach, or hydrogen peroxide. These treatments whiten the teeth but were thought to possibly alter their chemical composition.

However, the new research shows otherwise. The team discovered that these chemicals do not affect the key isotopes used in diet studies. This means that thousands of jaws from past decades are now usable in ways previously thought impossible.

“Most shark jaws in museums and private collections are chemically treated, so understanding if, or how these treatments affect tooth isotopes is crucial,” said Flinders research associate Dr. Lauren Meyer.

“Finding that preservation chemicals had no impact on isotope values opens the door for the use of jaws from historic collections across Australia and globally.”

This discovery means scientists can study shark diets without needing fresh tissue samples. It also significantly broadens the scope of possible studies, including comparative diet research across different eras and regions.

Chemical clarity through isotope testing

The study involved stable isotope analysis, which looks at carbon, nitrogen, and sulfur isotopes. These elements help identify where and what an animal has been eating.

“The chemicals in teeth provide a story of what the shark has eaten and from where, whether that be sea lions in South Australia, or tuna in New South Wales,” explained lead author Laura Holmes, from the Southern Shark Ecology Group in the College of Science and Engineering at Flinders University.

The researchers partnered with the Isotope Ratio Mass Spectrometry Laboratory at the University of Tasmania.

The team tested teeth from three very different elasmobranchs: cownose rays, gummy sharks, and broadnose sevengill sharks.

Despite their structural differences, all samples held up under isotope testing.

Rare species now within scientific reach

Access to historical jaws brings particular value when studying rare or threatened shark species. These species often cannot be sampled directly, but many have had jaws collected as trophies.

With these now validated as reliable data sources, older specimens can help researchers understand long-term dietary trends.

“This is especially useful for rare or threatened species, for which standard tissue samples may not be readily available, but for which trophy jaws have been collected, such as white sharks, tiger sharks, and makos,” said Dr. Meyer.

Older collections, such as those from the 1970s and 1980s, now offer a scientific window into the past. This information is crucial as many shark species face increasing pressure from human activities, climate change, and habitat degradation.

Applications across marine life

While this study focused on sharks and rays, the implications go beyond these groups.

Other marine predators, such as killer whales, sperm whales, and fur seals, also have teeth stored in museum collections. These could be tested using the same methods, opening new research pathways.

“This study opens the door to use a tremendous resource of samples to untangle the current and historic diet and foraging habitats of complex predators – making the most exciting finding from this study the capacity for new research that is now possible,” said Dr. Meyer.

These findings not only expand the toolkit for marine scientists but also enhance our understanding of ocean ecosystems over time. Every preserved tooth could tell a story.

The study is published in the journal Marine Environmental Research.

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