Mario Espinoza has dedicated years of his life to saving a fish he has yet to see for himself in Costa Rica’s waters. It’s not for lack of trying. Every single month, the University of Costa Rica marine scientist and his team drive to the edges of one of the largest mangroves in the world, where they load onto a former fisherman’s boat and work tirelessly over three days casting nets and longlines into the murky waters of the estuary. Under the shadow of 80-foot tall mangrove trees, with crocodiles and howler monkeys for company, they seek evidence of a ghost: the largetooth sawfish.

“You retrieve the longline hook by hook, and with every hook you’re retrieving, you’re crossing your fingers