The National Park Service is turning to the public for help in halting the decline in wildlife species that has persisted since humans on California's coast started skinning otters for hats and making breakfast of scrambled snowy plover eggs.

The Park Service and allied private organizations started a contest Tuesday called the Big Year aimed at aiding the Golden Gate National Recreation Area's 33 endangered and threatened species, including the California red-legged frog, the San Francisco garter snake and two runs of wild Chinook salmon.

People in the Bay Area can compete by sighting the species - some that are almost impossible to find - and logging the information on an interactive Web site. Participants are also asked to help with specific conservation efforts, such as planting tule reeds around frog ponds and writing lawmakers about the importance of protecting animals from butterflies to whales. Prizes haven't been determined, but the person who sees and helps the most species will be the winner.

And of all the parks, Golden Gate National Recreation Area hosts the most imperiled species. Park officials hope that the buzz created by the competition will draw attention to the need to protect and save the species.

The 79,000-acre park, a patchwork of lands once privately owned or under the military's control, supports an array of wildlife comparable in richness to that of the Hawaiian Islands and Florida Everglades.

There are 910 native plant species and 586 species of native fish, mammals, birds, reptiles and amphibians. There are another 500 nonnative species found in the national park.

"The San Francisco Bay Area is in the forefront around the country for environmental consciousness and commitment to sustainability. Yet in our own backyard, we're driving these species to the brink of extinction," said Brent Plater, the Big Year director who took on the project as member of the Sierra Club's National Wildlife and Endangered Species Committee. He also works as a visiting assistant professor at Golden Gate University's School of Law's Environmental Law and Justice Clinic.

Organizers have suggested specific conservation projects that could help each of the 33 species already in trouble because of pollution, loss of habitat, threats from nonnative species and climate change. Among the suggested conservation steps participants can take:

-- In Muir Woods, groups can help northern spotted owls by digging up invasive weeds that cover the hunting grounds and hide wood rats, the owls' food.

-- Restoring tidal wetlands around San Francisco Bay can boost habitat for the salt marsh harvest mouse. Ecologists plan to remove nonnative French and Scotch broom and pampas grass on Milagra Ridge above Pacifica to improve habitat for the Mission blue and elfin butterflies.

Officials are also encouraging people to do things such as reducing the amount of greenhouse gases they produce by using less energy. Switching from cars to public transportation is just one measure. Helping to avoid the worst effects of global warming could, for example, help the bay checkerspot butterfly, which may have trouble finding food because of changing temperatures. Likewise, Big Year organizers want residents to write to the National Marine Fisheries Service to request a speed limit for large vessels that could harm humpback whales in the Gulf of the Farallones National Marine Sanctuary.

Restoration effects have been successful in helping many species at the park.

A case in point is the effort to bring back the San Francisco garter snake and its favorite food, the California red-legged frog. By 2000, snake numbers had fallen so low that they couldn't be spotted in former habitats.

In 2004, the National Park Service, in an effort to help the snake, created a small pond at San Mateo County's Mori Point, one of the newest additions to Golden Gate National Recreation Area.

The California red-legged frogs moved into the pond in less than two weeks, said Alison Willy, a Fish and Wildlife Service biologist who analyzed the species at the pond. The next spring, the frogs had laid eggs in the pond.

"The park built the pond, it rained and the frogs moved in. It's a perfect example of if you build it, they will come," she said.

Last year, the pond was truly deemed a success when two snakes were seen foraging there, and now work is under way at three new ponds at Mori Point. Biologists want help from Big Year participants interested in helping put in native plants at the site. That volunteer work is scheduled every Saturday this month - a time when frogs lay eggs on aquatic plants.

"By increasing the frog population, our goal is to create an abundant and fine-dining experience for the snake. We hope snakes will slither in, be happy and will procreate and increase in numbers," said Sue Gardener, an ecologist with the Golden Gate National Parks Conservancy, a nonprofit partner of the park. "We've grown about 10,000 plants, and we're hustling to get them around the ponds."

Another key part of the Big Year program is the field trips organized to help show participants the species that are in danger of extinction. The trips, all of which can be found on the Web site, include:

-- A late afternoon trip to Muir Woods in March to look for northern spotted owls and pull weeds.

-- In April, experts will lead a trip to Milagra Ridge to look for the Mission blue butterfly. The same month and in May, groups will go to Mori Point to look for the California red-legged frog.

Some of the species will probably be impossible to find.

Botanists say the showy Indian clover hasn't been seen blooming in the park since it was originally found 100 years ago in Stinson Beach.

Tidewater goby fish are hard to find, as are Steller sea lions, which rest 27 miles out in the ocean at the Farallon Islands. Only the best birders will probably spot the marbled murrelets flying over park waters at Ocean Beach.

E-mail Jane Kay at jkay@sfchronicle.com.