San Diego Bay is the largest tidal estuary in California south of Morro Bay. While most of its northern shoreline has been converted to marinas, recreation beaches, and other urban uses, much of the southern portion has largely been acquired by the USFWS as the South Bay and Sweetwater units of San Diego National Wildlife Refuge. Other important beach habitat may be found on the Silver Strand portion on the west side of the bay up to Coronado Island, much of which is managed by the U.S. (incl. the Naval Amphibious Base, Coronado; Naval Air Station, North Isl.). Historic use (Western Salt Works) has resulted in the construction of large, shallow evaporation ponds that were alternately flooded and dried, which are now being restored for wetlands. An extensive, tidally exposed mudflat, rich in eelgrass, extends north of the ponds, and sizable patches of saltmarsh are also present, best developed at Sweetwater Marsh on the northeast portion of the IBA. Small areas of upland habitat, including grassland, riparian and coastal sage scrub, dot the eastern edge of the bay.

Ornithological Summary

The salt ponds within this IBA support large numbers of breeding terns, including a recently-formed colony of Gull-billed Tern, one of just a handful of colonies in the world of the rare vanrossemi race. A few dozen pairs of California Least Tern also nest here, as well as hundreds of pairs each of Black Skimmer, Caspian Tern and Forster's Tern. The Naval lands are even more important for breeding Least Tern, and recently supported nearly 1000 nests (T. Conkle, unpubl. data). Thousands of shorebirds utilize the salt ponds and adjacent mudflats during migration, especially Red-necked Phalarope and Western Sandpiper, with numbers approaching 20,000 in fall, and breaking 10,000 during winter and spring (Page and Shuford 2000). The patches of saltmarsh support several pairs of Light-footed Clapper Rail and about 100 pairs of Belding's Savannah Sparrow. Like other shallow coastal bays in California (e.g. Humboldt, San Francisco, Morro), the open water of central and south San Diego Bay appears to be very important to wintering coastal waterfowl, the vast majority being Surf Scoter and scaup. About 10% of the entire Pacific Coast population of Surf Scoters is thought to winter here, along with about 30% of California's wintering Brant (C. Sankpill, in litt.). San Diego County's only known breeding pairs of Peregrine Falcons nest adjacent to the bay, and forage year-round within the IBA. On the southeast side of the bay, the riparian habitat along the Otay River, though narrowly-channelized by earthen levees, supports a rich riparian avifauna.

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Conservation Issues

South San Diego Bay has been the site of numerous habitat acquisition and restoration efforts, but threats are similar to any urban site (exotic speices, human disturbance, encroachment, runoff, etc.). Current concerns involve recent efforts by a developer to construct a major residential center, including a 24-story hotel, on 100 acres (privately-held) at the entrance to Sweetwater Marsh (B. Collins , pers. comm.).

Ownership

Much of the southern portion has been acquired by USFWS as San Diego National Wildlife Refuge. Portions of the west side of the bay are owned by the U.S. Navy.

Habitat

San Diego Bay is one of the largest tidal estuaries in California. Historic use (Western Salt Works) has resulted in the construction of large, shallow evaporation ponds that were alternately flooded and dried, which are now being restored for wetlands. An extensive, tidally exposed mudflat, rich in eelgrass, extends north of the ponds, and sizable patches of saltmarsh are also present, best developed at Sweetwater Marsh on the northeast portion of the IBA. Small areas of upland habitat, including grassland, riparian and coastal sage scrub, dot the eastern edge of the bay.

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