Stewart Fallon

Radiocarbon dating helps save the lungfish

Scientists at the Australian National University have used the radiocarbon method to date lungfish scales in work critical to the conservation of the “living fossil” species under threat of extinction.

A team of scientists including Stewart Fallon and Kelly Strzepek, of the Research School of Earth Sciences, verified the method on scales from a lungfish from the Mary River in south-east Queensland.

The work will help to save the species whose lineage stretches back to the first air-breathing animals able to walk on land.

"Age determination is imperative to conservation because it underpins the understanding of population dynamics by revealing reproduction, growth and mortality rates," Fallon says.

"In most regions, the population size of lungfish is poorly understood."

Other dating methods used so far, including the counting of growth rings on lungfish scales, have been inaccurate, he says.

The new technique does not kill the iconic fish. "Wildlife managers will be able to pull a scale off fish they catch when they are logging length and weight data," Fallon says. "The whole exercise will take just a few minutes."

Radiocarbon, or carbon-14, is formed naturally in trace amounts in the atmosphere when neutrons hit nitrogen atoms. It forms carbon dioxide and enters the food chain. After tissue is formed, the radioactive isotope decays at a known rate to nitrogen-14. The amount of radiocarbon left in the sample reveals its age.

Fallon’s team measured the minute concentrations of radiocarbon on the ANU’s state-of-the-art single stage accelerator mass spectrometer from tiny samples taken from points along the scales obtained from a 1.25-metre-long fish found dead in 2008.

They detected the "bomb pulse", a surge in radiocarbon generated in the atmospheric nuclear weapons tests of the 1950s and 1960s.

The results, published in 2010 in the prestigious journal Radiocarbon by lead author Kelly Strzepek (nee James) (James et al., 2010), showed that the fish had hatched between 1940 and 1946.

Only three genera of lungfish remain in the world – in Australia, South America and Africa.

The sole Australian species, Neoceratodus forsteri, is listed as threatened under federal legislation. It once ranged across central, northern and eastern Australia but now clings to life in Queensland’s Burnett and Mary river systems.

People are encroaching on lungfish territory but the Federal Government stepped in to halt one big threat – the proposed Traveston Crossing Dam.

The mass spectrometer at the ANU’s radiocarbon dating centre is used in projects ranging from palaeoclimatology to archaeology.

James, K., Fallon, S.J., McDougall, A., Espinoza, T., Broadfoot, C., (2010) Assessing the potential for radiocarbon dating the scales of Australian Lungfish (Neoceratodus forsteri), Radiocarbon, Vol. 52, no. 3, 1084-1089.