In a time, long , long ago, I published some work on the kookiest of fish, the lungfish. Why am I telling you about this? To be honest I’m actually on holiday at the moment and wrote this before I left…But back to the fish. The lungfish have been at the centre of controversy in southeast Queensland for years, due to the inconvenience of them inhabiting areas earmarked for damming. Back in my honours year, being a marine scientist with no courses to take (economic geology just didn’t appeal at that stage), I took on a small project in the radiocarbon laboratory that would help managers ensure the survival of this primitive species. While the protection of the lungfish was not in question, the ability to draft a viable management plan was seriously hampered by the lack of available data on the most fundamental question in studies of population dynamics: how long do they live? The specimen I got my hands on turned out to have a minimum age of 55 years!
But lets take a few steps back Captain Planet, why might we care, and how did we get to that magic number?
Of the once extensive lungfish fauna there are only three populations left today: in Africa, South America and Australia. The single Australian species Neoceratodus forsteri, has a rich fossil history that extends to the Cretaceous and is part of a lineage found as far back as the Devonian. Molecular evidence suggests the descendants of the primitive lungfish species were the first to develop adaptations for an amphibious existence 380 mya and therefore represents the migration of species from sea to land.
Lungfish possess pectoral and pelvic fins connected by a continuous chain of bones, air-breathing lungs and distinct scales. The Australian lungfish only uses its well-developed air-breathing lungs during times of exertion or when water quality is particularly low. This adaptation enables their survival during flooding events that mobilize sand and silt in the water column. But in this instance it wasn’t the lungs we were interested in but the scales. Concentric growth rings on the scales have been historically used like counting tree rings however the accuracy of this aging technique was widely disputed. As the scale serves a protective function the full complement is attained quickly and remains fixed throughout the life history of the individual. This makes the deposition of new bands increasingly difficult to discern in long-lived species.
So rather than having to count rings I spent weeks cutting slivers off what looked like giant toenails (the scale was about 5cm long!!) and then radiocarbon dated each one to see if we could find evidence of the ‘bomb curve‘ (or evidence of fallout from weapons testing in the 50’s and 60’s) that would enable us to tie down known age markers and then produce an age model from it (see picture below). Rather ironic that nuclear weapons testing can be used for conservation, don’t you think?