When we were done we cleaned the skull and collected the teeth. Dolphins are born with one set of teeth that continue to grow a little bit each year. We can tell how old a dolphin is by cutting a thin section from the root of the tooth and looking at it under a microscope. We use a saw with a diamond blade to cut the tooth. Just like we can count the growth layers inside a tree trunk, we can count the growth layers inside a dolphin's tooth.
Scientists believe that a dolphin adds one growth layer each year.
From this information we can tell how long dolphins live and calculate their average life span. Using the dolphins' ages and other data collected from the necropsy , we can calculate growth rates and determine when dolphins become sexually mature. But we can't learn everything we need to know about dolphin biology from studying dead dolphins. We have to study live dolphins too. The federal law that protects dolphins also allows people to collect some alive for public display in oceanariums and for research , and the Indian River Lagoon was one place where dolphins were collected.