Sir Fish of the Stars.
Legacy of violence
reveals your true age.
The whale shark is the largest known fish species on the planet, with the longest specimen recorded at 18.8 meters. These gentle giants swim slowly through tropical waters, filter feeding on plankton and small fishes. No one is clear on how long-lived they are – like all sharks they lack the bony structures (otoliths) that are normally used to assess age in other fish species. Yet researchers now think they have the answer, and it lies in the legacy of the cold war.
Whale shark vertebrate have growth bands that increase as they age, rather like tree rings. The trouble is that without knowing how rapidly these bands form it is hard to use them to work out the age of a whale shark. Yet researchers have worked out a useful method of providing a scale for the growth bands by using the effects of nuclear weapons testing.
In the 1950s and 1960s nuclear bomb tests were carried out by countries on both sides of the Cold War, including in the atmosphere. The result of these tests is that the levels of the naturally occurring radioactive element carbon-14 temporarily increased, entering the food web – including whale shark vertebrate.
Ong et al. (2020) used radiocarbon assays of the growth bands of vertebrate from 20 whale sharks caught by the Taiwanese fishery before it was closed in 2007. They found the sampled whale sharks ranged in age from 15 to 50, and that growth bands appear to form annually. The importance of this is key to conservation efforts as understanding population structure is fundamental to understanding threats to the populations.
A note about ‘Whale shark’: Their size and nature mean that whale sharks are widely respected around the world, even featuring on the 100-peso note in the Philippines. Whale sharks are called ‘marokintana’ in Madagascar, meaning ‘many stars’ in reference to the white markings on their dark backs, whilst in Vietnam they are known as ‘ca ong’ – literally translated as ‘sir fish’.
Original research: http://dx.doi.org/10.3389/fmars.2020.00188