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Invasion of non - native plant species, especially smooth cordgrass ( Spartina alternifllora) and its hybrids, can result in degradation of habitat. Smooth cordgrass invasion causes excessive sedimentation, which can clog tidal sloughs used for foraging. The San Francisco Estuary Invasive Spartina Project is a coordinated regional effort among local, state and federal organizations dedicated to preserving coastal biological resources through the elimination of introduced species of Spartina (cordgrass). Cordgrasses are highly aggressive invaders that significantly alter both the physical structure and biological composition of our tidal marshes, mudflats and creeks (www.spardna.org). Maps on the Spartina Project website indicate that colonies of introduced Spartina occur in the vicinity of Redwood Shores and Bair Island. Appendix G of the Final Programmatic EIS /EIR for the Spartina Project (2003) identifies Best Management Practices for avoiding and minimizing indirect impacts from Spartina control activities on the California clapper rail. In a Biological Opinion regarding the Redwood Shores Levee Rehabilitation Project, the USFWS stated in 1996 that mercury accumulation in eggs was "perhaps the most significant contaminant problem affecting clapper rails in San Francisco Bay, with the south Bay containing the highest mercury levels." On the basis of data the Service collected in 1991 and 1992 in the southern portion of the estuary, the Service concluded that "the current accumulation of mercury in rail eggs occurs at potentially harmful levels "; the mean percentage of non - viable eggs was 29 percent (Medlin /USFWS, 1996). A 1992 study wherein 22 failed California clapper rail eggs from four south Bay tidal marshes were analyzed for organochlorines and eggshell thicknesses were measured. The study found that concentrations of all organochlorines except PCBs appeared to have declined since the mid 1980s, and eggshell thicknesses were statistically indistinguishable from those of pre -1932 museum eggs (Schwarzbach et al.). Predators. Dikes and levees serve as corridors for predators to access clapper rail habitats. Most predation occurs during the higher tides, when tidal channels are full of water and much of the vegetation is flooded; very high tides are more common in the wintertime (Albertson, 1996). At least 12 native and 3 non - native species prey on the clapper rail throughout its lifespan (Medlin /USFWS, 1996). The non - native red fox (Vupes fulva), Norway rat (Rattus norvegicur) and feral cats (Felix domesticus), are particular threats. To manage red fox predation, deemed potentially the most serious threat to clapper rail populations, the San Francisco Bay National Wildlife Refuge in 1991 implemented a predator management program, which has been somewhat successful. The program includes predator barriers, removal, and habitat management to make it less suitable for the predators. In addition, riprap installed along shorelines provides habitat for Norway rats, which prey on clapper rail eggs. Urban development close in to salt marsh habitat has increased predation by native raccoons, and electric power transmission lines that cross marsh habitats, provide hunting perches for raptors. The U.S. Department of Agriculture animal and Plant Health Inspections Service Wildlife Services (WS) entered into a cooperative agreement with the city of Redwood City to conduct predator management activities at Redwood Shores Peninsula to protect the California clapper rail and salt marsh harvest mouse from mammalian predators. The agreement is part of a requirement of the USFWS Biological Opinion dated September 5, 1996, regarding the Endangered Species Formal Consultation on the Redwood Shores Levee Improvement Project (Medlin /USFWS, 1996). Predator management activities began May 22, 2000, and have continued to the present. The following table summarizes information on the predators trapped by WS, based on periodic letter reports from WS to Mr. Peter Vorametsanti, Senior Civil Engineer, Redwood City (WS, 2000a, 2000b; 2001, 2002, 2004a, 2004b): M