Tomales Bay is situated in Marin County, about 40 miles north-west of San Francisco. This shallow bay averages about 1.5 miles in width and is about 12.6 miles in length, with an average depth of 12 feet (Johnson, Bryant and Hedgpeth, 1961). Oyster and herring comprise the main fishing industry, although the bay contributes a great amount of perch, smelt, halibut, and shark. Gill and seine nets are the most common gear used by fishermen. The primary objectives of this study were: (1) to determine the species composition of the bay, and the relation between seining success at different localities and such factors as tides and temperature; (2) to describe the life history of Phanerodon furcatus Girard, the most common perch of the bay.