Climatic effects on breeding seabirds of the northern Japan Sea

Seabirds as marine top predators have been put forth as reliable indicators of ecosystem change. To understand climate-ecosystem change in the northern Japan Sea, we studied the timing of breeding, chick diets, and breeding success of 3 seabird species almost continuously over 26 yr on Teuri Island, 1984 through 2009. Key climate drivers in this region are: (1) westerly winter winds that cool the atmosphere and the ocean and (2) the northward flowing Tsushima Current (TC) that warms the ocean in late spring and summer. Chick diet showed decadal changes in coastal pelagic fish, with a switch from sardine Sardinops melanostictus to anchovy Engraulis japonicus in the late 1980s corresponding to intensification of the TC. There were no long-term trends in the timing of breeding or breeding success of rhinoceros auklet Cerorhinca monocerata and Japanese cormorant Phalacrocorax filamentosus, but these variables were affected by interannual variation in spring air and sea temperatures, as well as the timing of TC warm water intrusions within the foraging range (similar to 60 km from the colony) of the birds. Effects include: (1) freezing of the breeding grounds by winter winds limiting access to nesting grounds and (2) availability of anchovy and sandlance Ammodytes personatus affecting chick diet, growth, and breeding success. We did not detect relationships between chlorophyll a concentrations and the availability of prey species. The timing and success of black-tailed gulls Larus crassirostris, which fed mainly on sandlance, however, could not be explained by these factors. Our study indicates potential links between the Pacific Decadal Oscillation index and the flow rate of the TC, and between the Arctic Oscillation index and local wind stress, and suggests that broad-scale atmospheric pressure fields influence local weather, oceanography, and seabirds indirectly through changes in prey availability.