Using sclerochronology, the science of tree rings, the sizes have led some scientists to hypothesize that predatory snails can live half a century or more, with females sending hundreds of thousands of tiny oysters out to sea over decades.

“The actual lifelong is significantly shorter,” said University of South Florida marine ecologist Gregory S. Herbert, who led the team.

The research further suggests that females give birth late in life. Because the largest equine conch living today is smaller and smaller than the historical shells used in the study, the article cautioned that “the largest females left in the wild could have few, if any, lifelong reproductive events,” putting the Gulf populations in crisis.

Like other marine animals that live near densely populated coasts, horse oysters have lost much habitat to evolution and pollution, including preferred breeding grounds along mudflats and seagrass beds.

Their Gulf habitat is also warming due to climate change, which scientists believe is increasing stresses on the animals, based on the negative effects of excess heat on other large mollusks.

But scientists say the most immediate threat to their numbers and sizes is overharvesting, primarily for their highly desirable shells.

The reported commercial yield in Florida declined from a peak of 14,511 oysters in 1996 to 6,124 oysters in 2000; to 1,461 in 2015; to only 67 in 2020, according to Florida Fish and Wildlife Commission data. Recreational harvest numbers are unknown.

pll/car/znc