Location of sampling stations in the Western North Pacific and their adjacent seas. From May 16 to 20 (right panel) and June 8 to August 2 (left panel) 2011. Open and solid symbols denote stations where sampling was performed during the day and night, respectively. Approximate positions of OY: Oyashio, KE: Kuroshio Extension and SAF: Subarctic Front are superimposed (cf. Yasuda 2003). Samplings were conducted during the following periods: Western North Pacific along 155° E line (38° to 44°N) from May 16 to 20, Okhotsk Sea from June 10 to 11, Japan Sea from June 8 to 24, East China Sea from July 1 to 9, subtropical Western North Pacific from July 11 to 12 and along the 155° E line (38° to 44° N), in the Western North Pacific from July 27 to August 2, 2011.