Calculate a Tarpon’s Weight

Researchers come up with new, harmless method to calculate the weight of tarpon.

A new research paper from Jerald S. Ault and Jiangang Luo updates allows anglers to make reliable weight estimations of their Atlantic tarpon catches.

Now, more than ever, tarpon weights are vital for tarpon catch-and-release tournaments, fish records and even scientific research.

Ault and Luo first analyzed a popular formula developed more than a century ago. They realized that the formula (Weight = Girth^2 X Length / 800) was “negatively biased.” It was under-estimating weights!


“What I found was, ‘Oh, crap, it’s negatively biased,'” Ault told the Miami Herald. “It underestimates weight by more than 15 percent.”

Their recent paper uses new statistical and analytical methods to predict weights based on measurements of tarpon body size.

The models were tested on data from more than 1,100 individual tarpon from Florida, the Gulf of Mexico, Caribbean Sea and western Africa.


Bias for their “new” formula was less than 1 percent, says the paper.


Above is an example of graph Ault created a couple years ago, using similar research methods.

Anglers can use a measuring tape to get the fish’s fork length and dorsal girth, then plug the numbers into a graph that Ault and Luo have created. Or, keep the measurements and plug them into the Tarpon Master 1.0 app on an iPhone. The app utilizes the new methods in digital form to instantly find a tarpon’s weight.


So far, the new estimator is being used by the Texas Parks and Wildlife Department and tournaments in Florida, Texas, Mexico, and Trinidad. It also provides a reliable means to estimate weights of tarpon of potential record sizes.


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