Marine bird populations were studied from 1 January, 1978, to 31 December, 1978, the first of two years, in the Strait of Juan de Fuca north to the San Juan Islands and Point Roberts and west to Sidney, British Columbi to determine their time of occurrence, distribution, abundance, and locations of important concentrations. Bird census methods included: (1) point census (2) sea watch, (3) beach census, (4) dead bird census, (5) small boat census, (6) ferry census, and (7) aircraft census. A total of 3,667 census sites and segments were sampled during 1978. Data were obtained on breeding marine birds on 138 islands in the study area. All field data were coded according to NOAA/NODC-approved codes and formats. Key-punched data were read onto a disk file and later transferred to a storage tape. After errors were corrected, two cross-reference programs were run to arrange data into appropriate order for later analysis. During the 1978 survey period, 43,353 records were generated on five record types. Computer output included total birds observed, standard deviation, number of censuses, weighted density, projected total numbers, percent of projected total numbers (for each species), biomass, percent of projected total biomass, and bird oil index. The study area was divided into 13 regions and 64 subregions. Where appropriate, open water and shoreline habitats were treated separately since they differ biologically. Approximately 94% of a total of 29,600 pairs of 12 bird species nest on 35 islands in the San Juan Islands, Smith and Minor Islands, Protection Island, and Tatoosh Island. The most abundant breeding species are the Rhinoceros Auklet (60% of total) and the Glaucous-winged Gull (24% of total). Seasonal distribution, abundance, and species composition are discussed according to region. Data for Swiftsure Bank are limited but indicate that it is typical for offshore waters of this coast. The Strait of Juan de Fuca, Outer and Inner regions, are especially important because of the large number of Common Murres present in the Summer and Fall (nearly 240,000 birds). The shoreline subregions of these regions are radically different than the open water. Large numbers of ducks, geese, gulls, alcids, and shorebirds are present east of Port Angeles to and including Discovery Bay. Jamestown has a particularly high density of waterfowl in Spring and Fall. Admiralty Inlet is important as a migration and local movement corridor between southern Puget Sound and the Strait of Juan de Fuca. The Anacortes to Hale Passage and Georgia Strait—Eastern regions include many bays that are very important habitat for large numbers of Black Brant, scoters, and other waterfowl as well as Western Grebes. Padilla Bay is important habitat for Summer nonbreeding ducks. As many as 50,000 Dunlin as well as other shorebirds use Boundary Bay during migration. Large numbers of scoters and other diving ducks, loons, grebes, and alcids are found in the Georgia Strait--Western region. Many birds are attracted to herring spawn in the Spring. Noteworthy concentrations of Oldsquaws, Common Murres, Marbled Murrelets, and Arctic Loons are found in the Winter. The portion of Haro Strait within our study area has low numbers of birds primarily because it includes deep waters and small amount of shoreline. Rosario Strait is characterized by large numbers of feeding gulls, alcids, and cormorants. Numerous breeding and roosting sites are present in Rosario Strait. The San Juan Islands-Northern Waters region has few nesting colonies and overall numbers of marine birds are low. The San Juan I slands-Interior Channels and Passages region also has low numbers, with Pelagic Cormorants, though concentrations of Glaucous-winged Gulls, and Rhinoceros Auklets are especially important in Summer. The San Juan Islands-Interior Bays region is characterized by localized high Winter concentrations of diving ducks, Horned and Western Grebes, and Mew Gulls. Diversity is much higher than in the preceding two regions. Active Pass is the most important feature in the Canadian Waters region. Large feeding flocks of 7,000 birds are frequently seen in Winter. Abundant species include Brandt's Cormorant, Arctic Loon, Common Murre, and Bonaparte's Gull. Based on beached bird censuses, present marine bird mortality is low. The maximum rate observed is 1.47 dead birds/km/census.