The Australian lungfish (Neoceratodus forsteri) is a protected species listed as vulnerable to extinction and yet has many knowledge gaps hampering sustainable management and extinction risk. Understanding their population age structure is key for the management of a threatened species. N. forsteri are the oldest living vertebrates on earth and have many features atypical of modern fish, hampering the use of common fisheries population assessment methodologies. Traditional fish ageing techniques involve destructive sampling of otoliths (calcium carbonate structures in the inner ear), vertebrae or other hard parts, or non-destructively using external bony body parts like scales or spines, to interpret patterns of annual check marks forming in these structures. Lungfish do not have hard otoliths and lack external spines, however they possess thick scales with apparent markings analogous to check marks, however efforts to age them from these marks has proven inconclusive. To overcome this problem we have developed a novel technique by measuring the amount of radiocarbon trapped in their scales while they grow. Radiocarbon has been successfully used destructively to age fish from otoliths and other hard bony parts of fish, but this is novel in that a non-destructive method has been developed using scales from a long lived protected species. In this method, we compare the atmospheric radiocarbon pattern derived from atomic weapon testing in the 1950-1960s to a series of <1mm slices removed sequentially from the scale. We have aged 90 fish from the Brisbane, Burnett and Mary Rivers. The data support the view that lungfish are long lived with 35% of the fish aged being at least 50 years old in 2014. The data also suggest gaps in the recruitment of Lungfish during the past 50 years. Environmental factors and habitat destruction are being examined as possible drivers for the recruitment gaps.
The presentation will start with an introduction to radiocarbon dating, then will explain the term “bomb” radiocarbon and how we can accurately date items over the past 60 years using the radiocarbon “bomb” curve.