Puerto Vallarta, Mexico (CNN) -- A lifelong nature lover, Oscar Aranda studied biology in college and knew he wanted to work somehow with animals at sea.
But he didn't find his calling until years later, when he was summoned to a beach and saw a gruesome scene that would change his life.
"I found a turtle chopped in pieces in a bucket, and its heart was still pounding," Aranda said. "[The police] needed my help to decide what to do.
"When you see how the people kill [sea turtles] and how they are just using them for their meat and eggs -- it's sad."
There was nothing Aranda could do to save the turtle that summer night 10 years ago. But ever since then, he has patrolled Puerto Vallarta's beaches as an unofficial keeper of the sea turtle maternity ward.
Aranda's conservation group, La Sociedad Ecológica del Occidente, is dedicated to protecting turtles that nest along Mexico's northwest Pacific beaches. From June through December -- prime nesting season -- Aranda and his unpaid volunteers watch over the shorelines where the turtles lay their eggs.