Ever since humans came on the scene, shark populations along coastlines have been declining, so it’s hard for scientists to know where to set conservation goals. We don’t really know what a healthy shark population was several thousand years ago because humans only started keeping count about a hundred years ago. UC Santa Barbara ecologist Erin Dillon landed on a cool but painstaking way to estimate how many sharks might have been hanging out around a coral reef seven thousand years ago. (Originally aired July 28th, 2021)