MOSS LANDING -- From basking sea lions to surfacing whales, no vacation to the Central Coast is complete without a sighting of a marine mammal.
But holiday snapshots are not the only pictures the charismatic ocean dwellers have to offer. Scientists are increasingly finding ocean mammals are valuable sources of information about
diseases and toxins found in coastal waters.
The most recent research has focused on harbor seals, who live from birth to death just off shore.
"I view them as samplers for the environment," said Stephanie Hughes, a recent graduate of the Moss Landing Marine Labs and marine scientist who researches diseases in seals.
The seals, whose territory ranges from Alaska to Mexico, live close to humans and eat many of the same fish that people do, including sardines and salmon. They scoop up sediment full of human contaminants when they swoop to the sea floor for bottom-feeding fish.
"Seals do similar things that we do, in the same places. So if seals can get something, then people ask, 'Well, what if I swim in the bay?'" said Denise Greig, a marine scientist who studies chemical contamination in seals at Sausalito's Marine Mammal Center.
In a recent study of water from San Francisco to Monterey Bay, Greig and her colleagues found Monterey Bay seal blubber had high levels of pesticides and other agricultural chemicals, while San Francisco Bay seals were full of flame retardant chemicals and other industrial toxins.
To better track the local trends, the Marine Mammal Center plans to make "disease maps" for the California coast. Scientists are using the past 10 years' worth of data about diseases in stranded seals, sea lions and whales captured by mammal labs from San Diego to Sausalito.
The center's scientists are looking at health issues, including injury, illness and toxins from human contamination of the ocean.
"The idea is to track trends and find hot spots, both where and when. Then we can address why," said Frances Gulland, the center's head veterinarian.
Gulland hopes the disease map will serve as a model for similar projects around the world -- perhaps in New England, where hundreds of harbor seals died of bird flu in 2012.
"We want to monitor so we don't reach that level of, 'Oh, jeez, we have this disaster, where did it come from?'" Hughes said. "These animals are sick, but we don't know why."
Another recent study highlighted how research on seal diseases can help protect the health of humans.
A collaboration among Moss Landing Marine Labs, the Marine Mammal Center and UC Davis tested 500 seals for Vibrio, a family of bacteria that includes cholera and food poisoning bugs. Hughes, Greig and Gulland were co-authors on the paper. They collected samples from seals from California's North and Central Coasts in 2007, 2008, 2010 and 2011.
Many seals were infected with Vibrio, some with strains that could be dangerous to humans. Depending on the type, said the U.S. Centers for Disease Control and Prevention, the bacteria can cause anything from mild food poisoning to sepsis and death -- though none of the seals had the deadly strains.

A recent report by the CDC showed regulations banning raw oysters fished from the Gulf of Mexico from April to October every year has slowed Vibrio infections in humans. The regulations even completely halted California cases of Vibrio vulnificus, the most dangerous form of the bacteria, which recently killed people in Florida.
The Vibrio study was "only four years. So it would be nice in the future to be able to have more of a sample and say, 'Is this increasing over time?'" said Sarah Peterson, a marine scientist at UC Santa Cruz's Long Marine Lab. "Is there something that's changing in the environment to cause it to be more prevalent?"
Marine scientists say it will take more than one species to get a good picture of the coastal ecosystem. Another marine mammal they would like to focus on is the sea otter, which shares a similar place on the food chain as the harbor seal.
Sea otters have been dying of everything from the drug-resistant staph bacteria that are terrorizing hospitals, to toxoplasmosis, a parasitic disease that makes it dangerous for pregnant women to change the litter box. Sea lions, who swim much farther out than seals, will eventually tell scientists about contamination in deeper water.
Researchers say as humans continue to adversely affect the seas through pollution and global-warming emissions that raise sea levels, they need all the help they can get.
"The environment is changing and we should be aware of those changes," Hughes said. "Then, if something happens, we'll have the data to know how we can mitigate it."