Declines in marine bird populations in Prince William Sound, Alaska coincident with a climatic regime shift

Analyses of marine bird surveys conducted in Prince William Sound, Alaska i n July 1972 were compared to surveys in July 1989, 1990, 1991, and 1993 and indicated that populations of several taxa of marine birds that prey on fi sh have declined in Prince William Sound, but most taxa that feed on other prey species, such as benthic invertebrates, have not declined. Red-throate d Loon (Gavia stellata), Pacific Loon ( C. pacifica, cormorant (Phalacrocor ax spp.), Surf Scoter (Melanitta perspicillata), Bonaparte's Gull (Larus ph iladelphia), terns (Sterna spp.), Pigeon Guillemot (Cepphus columba), Brach yramphus murrelets (Brachyramphus marmoratus and B. brevirostris), Parakeet Auklet (Cyclorrhynchus psittacula),Tufted Puffin (Fratercula cirrhata), an d Horned Puffin (Fratercula corniculata) populations declined by >50%. Most of these are piscivores, feeding on schooling fish. Some non-piscivorous t axa, such as Harlequin Ducks (Histrionicus histrionicus), goldeneyes (Bucep hala clangula and islandica), and Black Oystercatchers (Haematopus bachmani ), have increased in Prince William Sound between 1972 and 1989-1993, altho ugh a portion of the population was killed by the T/V Exxon Valdez oil spil l. Declines in piscivorous bird populations also have been documented in th e Gulf of Alaska, the Baring Sea, and along the California coast in the pas t two decades and have been coincidental to changes in forage fish species in the North Pacific Ocean. Many of the declines ap pear to be related to c hanges in forage fish abundance that occurred during a climatic regime shif t in the north Pacific Ocean, although some taxa were also affected by the Exxon Valdez oil spill.