Distribution of migrating Short-tailed Shearwater and breeding Rhinoceros Auklet and their prey in the northern Sea of Japan, Hokkaido in spring

Abstract

A survey of the at-sea distributions of 1) planktivorous Short-tailed Shearwater Puffinus tenuirostris, migrating to their northern summering area and 2) piscivorous Rhinoceros Auklet Cerorhinca monocerata, breeding in the northern Sea of Japan off Hokkaido, was carried out by ship, from 16 to 28 May 2008. Avian censuses were combined with: acoustic surveys aimed at measuring prey density, and sea surface temperature (SST) surveys. Surface Chlorophyll a distribution was obtained using satellite imagery. The density of shearwaters was correlated positively with 200 kHz S_A (the index of density of zooplankton including krill) at the 10 km scale, and 200 kHz S_A was correlated negatively both with SST and Chlorophyll a. However, shearwater densities were not correlated significantly with SST and Chlorophyll a. The result suggest that migrating shearwaters may be able to find patches of krill in cold water. In contrast, the density of Rhinoceros Auklets was not correlated with 38 kHz S_A (the index of pelagic fish density) or 200 kHz S_A at any scale.