Point Reyes, Calif. ? Two juvenile California sea lions paused for a moment at the edge of the sea, each raising their whiskered faces toward the silvery water before sliding in to freedom.

For the Marine Mammal Center crew standing behind the rehabilitated pinnipeds on Thursday, it was a significant day: rescued sea lion No. 10,000, nicknamed Milestone, and 10,001, Zodiac Girl, had been nursed back to health and sent back to the wild where they belong.

“There’s always some attachment. There’s always some animal that captures your heart,” said Shelbi Stoudt, the center staffer who organizes these regular releases. “It’s a bittersweet feeling because you’re sending them back home but you also don’t get to see them anymore.”

Since it opened its doors 36 years ago, the nonprofit marine mammal hospital has become famous for nursing sick marine critters back to health — but its biggest contribution perhaps has been its role in collecting and storing thousands of tissue and other samples from the animals it rescues along 600 miles of California coast. The center’s mix of laboratory science, marine zoo and educational outreach has led to dozens of published scientific papers and helped push understanding of effects of toxic algae, disease and the effect of climate change on these coastal denizens.

While rescues are a chief focus of center, only about half of the animals the center takes in survive to be released. Still, many of the more than 17,000 marine mammals — including entangled whales, otters and elephant seals — the center has aided or taken in have contributed samples that will help further research that can aid threatened and endangered species around the world.