Mature chum salmon (Oncorhynchus keta) were caught in bottom trawls off lwate Prefecture, northern Japan, in autumn. To document the incidence and depth distribution of these catches, records were kept of salmon caught by five trawlers that fished along the Pacific coast of northern Honshu during September–December 1986. During this period, 4337 chum salmon were caught at bottom depths ranging from 150 to 460 m with most taken from 200 to 350 m. Gonads and stomach contents were examined for 100 of these salmon. All were mature and close to spawning. Thirty-nine of the 100 stomachs examined were empty and the remaining 61 contained only a small quantity of food, averaging 2.4 g. Chum salmon may move at these depths to avoid the high temperatures of surface waters (12–20 °C) found in this area and to follow temperatures close to their thermal preferendum (3–11 °C) which are found near bottom. This phenomenon appears to be an adaptation of chum salmon near the southern limit of their range.
The Utilization of Cold-water Zooplankton as Prey for Chum Salmon Fry in Yamada Bay, Iwate, Pacific Coast of Northern Japan
