Jun 27, 2008

Imperiled snake to get habitat makeover

By Julia Scott / Bay Area News Group

The Peninsula's most tenacious population of endangered San Francisco garter snakes is about to make a major comeback in a little-known urban canal system steps away from a concrete jungle of airport runways, highway onramps and railroad tracks.

San Francisco International Airport's team of planners and environmental engineers is in the final stages of preparing for a 10-year, $4 million project to redesign two urban storm water canals that also happen to be prime habitat for the San Francisco garter snake. The construction project, to begin in mid-August, will dredge four miles' worth of canals that provide flood control for the airport while creating a veritable snake paradise of burrows, swimming holes and hunting sites for prey.

Motorists southbound on Highway 101 would never suspect they were speeding by this little oasis of willows and acacias along the banks of a channel that stays wet through the summer. It is this place - Cupid's Row Canal in San Bruno, along with the South Lomita Canal in Millbrae - that the San Francisco garter snakes have been restricted to for the last 50 years as the surrounding land has been filled with malls and subdivisions. Their days are filled with the clang of Caltrain going by and the continuous rumble of airplanes overhead.

The habitat enhancement project, which is now seeking an environmental permit from San Francisco and several state agencies, evolved out of an incident in 2003 when a storm flooded the neighborhood around the Cupid's Row Canal. Both canals suffer from silt buildup and require regular dredging, but dredging can be tricky because of potential impacts to the garter snake and the California red-legged frog, its main source of food.

The solution SFO officials settled on was to re-engineer the canals - creating sediment traps that would minimize the need to dredge as often, and widening the canals to create still pools for the red-legged frogs to lay their eggs in. The next time they have to maintain the canal a decade hence, SFO officials hope the snake and frog populations will have rebounded so strongly that getting a permit won't be quite so complicated.

"It's like expanding their subdivision. There's more space for them to set up their burrows close to the water," said Ernie Eavis, deputy airport director and chief engineer, walking next to the Cupid's Row Canal on Thursday.

The San Francisco garter snake has been listed as endangered since 1967, its wetland habitat threatened by development while its prey, the red-legged frog, became correspondingly rare (it is now listed as a threatened species). By 2004, the snake was so scarce that state officials were asking the public to help find the remaining population so it could be protected. In 2005, five pairs of snakes were transported from the Netherlands to San Francisco.

A few pockets of the distinctive blue-and-brown snake remain, mostly in select coastal areas of the county (such as Mori Point in Pacifica) and in parts of coastal Santa Cruz. Scientists believe they originated in the flatlands around what is now Highway 280.

But the largest known population of San Francisco garter snakes on the Peninsula, and indeed in the Bay Area, now exists in the narrow "West of Bayshore" area owned and maintained by SFO. The U.S. Fish and Wildlife Service has been aware of their presence there since the 1970s, but were under the impression that their numbers had dwindled in recent years. They were proved wrong by a study, conducted this spring, that found between 400 and 500 San Francisco garter snakes at both canals.

"It's hard to tell how long the snakes have been there. It's completely surrounded by development, so it's like a little island population. That population is going to be isolated from all the others, but at one time they were probably able to go up the watershed and communicate with all the others," said David Kelly, a Fish and Wildlife Service biologist familiar with the project.

The snakes' survival becomes even more impressive considering how close they came to being wiped out by development. Only the fact that SFO bought the land in the 1920s spared their habitat.

"That's the good thing about that airport - they are preserving all that land. Since the snake is there, state and federal regulations would make it very, very difficult to develop," Kelly said.