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.
Indeed, many of the animals nursed back to health are not facing imminent extinction _ there are about 200,000 California sea lions in the wild _ but the their maladies and their genetic makeup are similar to other species in peril.
California Sea Lions share genetic traits with Steller sea lions, which are a threatened species. The center's researchers say collecting and banking scientific samples from many of the thousands of sea lions the center has treated contributes to efforts to save Stellers. Same goes for elephant seals, which share traits with the endangered Hawaiian Monk Seals.
"We're learning about marine mammal health through all these patients. Before 1975, there was never anything being regularly documented..., so it wasn't feasible to get baseline sets of urine and tissue samples," said Jim Oswald, the center's spokesman.
Though Milestone and Zodiac Girl unwittingly became the center's 10,000th and 10,001st sea lions to be sent back home the Pacific Ocean, their time spent at the center's facility in the Marin Headlands just north of the Golden Gate Bridge provided scientists with a little more information being used to unravel a mystery ailment.
The two animals had leptospirosis, a bacterial infection that attacks the kidneys and can be fatal to sea lions. Dogs and humans can also contract the disease.
What's odd about the affliction, scientists have observed, is that it occurs cyclically every four or five years, when hundreds of sickened, stranded California sea lions are found infected. While no answer to the mystery has been found, the center's data collection is helping researchers move closer.
The center is studying the exposure of sea lions to carcinogens. About 17 percent of the stranded adult sea lions taken in by the center have a specific cancer the center first found in 1979.
Researchers are studying the animals for levels of carcinogens, such as the persistent pollutants DDT and PCBs, which are banned in the U.S., but still are found in sea lion blubber.
Oswald said the center also finds chemicals, antibiotics and other substances of human origin in elephant seals and other creatures it studies.
The cancer research is being done with an eye to improving the understanding of human cancers, and allows scientists to do tests that could not be done with human subjects.
"It's shocking how many animals we've treated, but the information we've received from them, that's one of the most important aspects of the center's work," said Stoudt.
The Marine Mammal Center: http://www.marinemammalcenter.org/
Jason Dearen be reached on Twitter at http://twitter.com/JHDearen