Audubon California and the San Pablo Bay National Wildlife Refuge in December 2010 completed the restoration of 65 acres of tidal marsh, sub-tidal, and marsh-upland transition environments on the Refuge at Lower Tubbs Island. The milestone followed two years of fundraising, planning, monitoring, and permitting, and construction. The project goals were to support the re-establishment of native vegetation, improve estuarine-dependent wildlife habitats, and reduce or eliminate future mosquito population management issues. These benefits are expected through improvement of hydrological flow and tidal flushing, re-established connections between marsh areas, and restoration of native plants along the marsh-upland transition zone. Internal levees and sills, which form barriers to tidal flow and circulation, were breached or removed and new channels that re-connect marsh areas to existing drainages were excavated.
To measure the effectiveness of project actions, Audubon, refuge staff, and volunteers have collected baseline biological data for the site prior to construction. This data will be compared to post-construction data to be collected over the next five years. Control sites will also be surveyed to allow for comparisons among similar landscape types before and after construction. There are numerous opportunities to volunteer with this project and help our monitoring efforts. Volunteers can assist with small mammal trapping, song bird point counts, waterbird surveys, vegetation transects, and native plantings.
The Refuge lies along the northern border of San Pablo Bay and was established in 1970 for the purpose of protecting and providing habitat for migratory birds and species listed as endangered or threatened. The 249-acre project area encompasses the Lower Tubbs Island and Tolay Creek units of the Refuge. Hydrology of Lower Tubbs Island is characterized as muted tidal and exchanges tidal water with San Pablo Bay and adjacent marsh units through a series of perimeter channels and culverts. The unit contains several interior man-made levees, culverts and waterways that functioned to improve duck habitat when the site was a hunting club prior to the 1970’s. The vegetation is dominated by native tidal marsh-adapted species such as pickleweed (Sarcocornia pacifica), salt grass (Distichlis spicata), Pacific cordgrass (Spartina foliosa), sedge (Scirpus maritimus) and gumplant (Grindelia stricta). The Tolay Creek unit of the Refuge (435 acres) includes approximately 5.6 kilometers of creek and associated tidal environments south of Highway 37. Human activities such as levee construction and conversion to agricultural land have dramatically altered the landscape of Tolay Creek, decreasing the size of the tidal flood plain and associated marsh. The open water and tidal creek channel areas contain little vegetation, except for Spartina foliosa and patches of in the transition zones. In addition, the area provided poor habitat for wildlife. Common plants of Tolay Creek tidal marsh include pickleweed, saltgrass, jaumea (Jaumea carnosa), and alkali heath (Frankenia salina).
Levee vegetation of the Lower Tubbs Island and Tolay Creek units consist largely of native coyote bush (Baccharis pilularis) intermixed with native and non-native perennial plants. Non native species dominate plant cover along levees and include the invasive perennial pepperweed (Lepidium latifolium), yellow star thistle (Centaurea solstitialis), fennel (Foeniculum vulgare), and mustard (Brassica spp.), and non-native grass species (e.g., Bromus diandrus).
Endangered Species and Migratory Birds
The federal and state endangered salt marsh harvest mouse (Reithrodontomys raviventris) and California clapper rail (Rallus longirostris) occur within the project area. The project area also supports several state listed or Species of Concern such as the California black rail (Laterallus jamaicensis), San Pablo song sparrow (Melospiza melodia samuelis), salt marsh common yellowthroat (Geothlypis trichas sinuosa). The presence and distribution of these species is directly related to the quantity and quality of available habitat. Areas where tidal water impoundments occur in conjunction with poor vegetation health are less likely to support these species because of poor habitat conditions. At least 13 species of waterfowl and 30 species of waterbirds use the Tolay Creek and Lower Tubbs Island units during some portion of the year. Intertidal mudflats of the project area are used extensively by shorebirds.
The project area contains historic tidal environments that experience impeded tidal flows from remnant dikes and levees. These conditions have resulted in stagnant pools of water that cause plant mortality or reduce health and encourage above normal mosquito production. Application of pesticides by the Marin-Sonoma Mosquito and Vector Control District occurs when mosquito numbers exceed established thresholds. These pesticides affect mosquito and other invertebrate species used as food by native wildlife and access for mosquito management causes disturbance to wildlife and plant populations. Climate change associated sea level rise and higher intensity storms are likely to exacerbate tidal impoundment issues and stresses on levees.
Enhancement and restoration of tidal flows at Tubbs Island and Tolay Creek may enlarge the area of shallow channel habitat and tidal marsh interior mudflats. Increased tidal prism would also enlarge existing deep channels to the benefit of fish and diving ducks. Increasing the area of healthy tidal marsh would expand habitat for endangered tidal marsh species such as the California Clapper Rail and the salt marsh harvest mouse. Enhancing existing tidal environments would also benefit plants and rare bird species such as the San Pablo Bay song sparrow and saltmarsh common yellowthroat that depend on the marsh and upland transition zone. Expansion of marsh interior mudflats within the project area would provide important high tide roosting and foraging environments for migratory and wintering shorebirds and waterfowl.