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Bay Creeks Get Good Report Card

Asked to foresee the ecological fate of a stream meandering from home-packed hills through grimy city streets and shoreline industrial zones to the Bay, anyone might presume the worst. And until recently - with decades devoted to putting urban creeks behind dams and into underground pipes and concrete channels - they would have been right. But the creeks that still weave through today's metropolitan Bay Area are holding their own, ecologically, according to preliminary results of a 1994-1997 survey of 30 local watersheds.

The survey, conducted by U.S. EPA's Robert Leidy for the S.F. Estuary Project, sampled over 300 sites - noting what species of native fish swam the pools and riffles, as well as how well water flowed, habitats connected and bank vegetation thrived. "Things are better since my 1984 survey," says Leidy. "There's been a halt to degradation in some areas, probably due to the push for Clean Water Act enforcement and stormwater control over this last decade, as well as to watershed protection by various land management agencies like the S.F. water department and the Peninsula Open Space District, and to growing interest in creeks by local groups."

According to Leidy, at least 75% of fish species native to Bay creeks are maintaining healthy populations, an indication that their small stream habitats are in "pretty good shape." During the study, Leidy found a total of 16 native fish species in Estuary streams including lampreys, trout, salmon, minnows, a sunfish and a surf perch. Rainbow trout or steelhead occurred at 41% of the sampling sites, with small runs of steelhead found from San Jose's Guadalupe River to Alameda's San Lorenzo Creek, Marin's Corte Madera Creek, and Contra Costa's Walnut Creek. In addition, Leidy documented small spawning runs of chinook salmon in four Bay Area creeks. The most common minnow found by Leidy was the California roach - occurring in 43% of sites; the most unique species, a thriving population of hardhead in the middle reaches of the Napa River (the only population outside the Central Valley, where surveys suggest this minnow is declining); and the rarest species, the splittail (a candidate for listing) and the Sacramento perch - now vanished from all Bay Area streams save one. Fish and game agencies stocked the perch in various reservoirs throughout the western U.S. In the Bay Area, only one "natural strain" remains in some abandoned gravel pit ponds in the Alameda Creek drainage, says Leidy.

Some of these fish were recorded as part of "fish assemblages" of 6 - 10 species - groups of species normally associated with each other under natural healthy conditions. Leidy found such healthy assemblages - and conditions in which natives dominated and exotics were uncommon and absent - in portions of many Estuary watersheds, in particular in Sonoma Creek, the Napa River, and upper Coyote and Alameda Creeks. "People have a tendency to go to more remote, rural areas to look for good creek resources, or to focus on big plumbing in the Delta," says Leidy. "But many Central Valley streams are pretty trashed. I wanted to look here in our urban estuary."

Leidy's final report will debut this fall. In the meantime, he's developed a list of 18 creeks or watersheds that are high priority candidates for protection (see below). To develop the list, Leidy measured 11-15 biotic and physical factors and then combined them into a functional index of stream health. Factors rated included such things as the diversity and abundance of native fishes and amphibians; flow patterns (such as natural flood and drought flows); and habitat conditions, arrangement and connectivity. The resulting preliminary list will be finetuned for release this fall, with the eventual aim of identifying the best candidates for creating "Aquatic Diversity Management Areas" - the aquatic version of ecosystem and multi-species management zones.

"This report will allow planners and municipalities to focus resources on drainages that are in good shape or have unique elements," he says. Indeed Leidy's results suggest the Bay region can provide important repositories of aquatic biodiversity in a state in which much of this diversity in endangered. Of California's 116 fish taxa native, 7% are extinct, 13% are formally recognized as threatened or endangered by state and federal governments, 23% qualify for such formal listing, and 19% may qualify in the near future if present population trends continue. According to Leidy, only 23% of the native freshwater fish fauna of California can be regarded as "secure."

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