Archive for September 12th, 2019

Alligator Gar and Thermonuclear Weapons Testing

Thursday, September 12th, 2019
Alligator Gar

Alligator gar: What a lovely smile.

This is Passport to Texas

Here’s a fish story about alligator gar, a curious biologist and thermonuclear weapons testing.

We’ve done a lot of work recently on the alligator gar. Being able to accurately age these fish is important. Because it tells us not only how long they live, but how they grow and in what years they were produced.

Dan Daugherty is a biologist with Texas Parks and Wildlife.

Fish have structures called otoliths that are like the bones in our inner ear – they accrue a layer of calcium carbonate each year of the fish’s life. If you remove the otolith and section it, you can see growth bands like the rings on a tree stump. Count the rings and estimate of the age of the fish. We estimate that some Alligator Gar caught in recent years at over 60 years old. But counting that many rings on a small structure is difficult. So, to verify our ages, we turned to radiocarbon.

You may know it as Carbon-14. But how is it used to age this fish?

Radiocarbon, or carbon-14, is a rare carbon isotope, naturally occurring at about 1 part per trillion. However, thermonuclear weapons testing in the 1950’s released massive amounts of this isotope into the environment, which was absorbed by all organisms at that time. Given that some of these fish were estimated to be over 60 years old, they would have hatched around that time. And, if the fish were truly that old, then we should measure high levels of radiocarbon in their otoliths. When we analyzed the radiocarbon concentrations in the otoliths, they matched the levels found in the environment in the 1950s, confirming the accuracy of these Alligator Gars’ age.

Now that’s a fish story for the ages.

For Texas Parks and Wildlife…I’m Cecilia Nasti.