Permalink : http://hdl.handle.net/2115/38468

KEYWORDS : Black-tailed Gull;Diet;Sand lance;Japanese Anchovy;SST;Tsushima current

Availability of fish as the prey of seabirds undergoes extreme changes under temporal and spatial variations of marine environments. Successive monitoring of prey species and breeding performance of seabirds at different colonies may clarify a part of the effects of these variations of marine environments. Prey species and growth rates of chicks of Black-tailed Gull Larus crassitostris at Teuri and Rishiri Island, Hokkaido, Japan, were measured from 1998 to 2006, and the effects of sea surface temperature (SST) were analyzed. At both islands, 0 + and > 1 + Japanese sand lance Ammodytes personatus and Japanese anchovy Engraulis japonica were main prey of chicks. At Teuri Island, chicks grew rapidly in the year when SST anomalies in June was low, except for 2006 when SST in June was extremely low, although prey species composition did not affect growth rates. At Rishiri, in the year when SST anomalies in July was high, the mass proportion of anchovy was small but that of 0 + sand lance was greater, and chicks grew rapidly, except for 2006 when SST in July was extremely high. The results suggest an increase in availability of (i) all prey species when SST in June is high or low outside of optimum range at Teuri, and of (ii) 0 + sand lance during high SST in July at Rishiri. Although the two islands are just 90 km apart, prey species determining chick growth of Black-tailed Gull and the marine environmental factors that enhance the prey availability seem to be significantly different in them.