Food Habits of Walleye Pollock Inhabiting the Mesopelagic Zone in the Northern Japan Sea in Spring and Autumn.

Abstract

The diet and feeding intensity of walleye pollock Theragra chalcogramma were investigated in April and October 1993, and in April 1994. Specimens ranging from 262 to 456mm in standard l ength were sampled with a mid-water trawl off Hiyama Subprefecture and Aomori Prefecture in the northern Japan Sea. The main food items were large-sized zooplankton. In April, pollock fed chiefly on euphausiids (Thysanoessa longipes), chaetognaths, and hyperiid amphipods (Themisto japonica). In October, the main food organisms were hyperiid amphipods (T. japonica). Stomach-content weight indices indicated that the feeding intensity of pollock was stronger in April (after spawning) than in October (before spawning). The numerical compositions of food categories in April differed among sampling stations. Such differences were not observed in October. It seems likely that the dis tinct variation of diets in April is ascribed to geographic differences in zooplankton composition in the mesopelagic zone.

Diel changes in vertical distribution patterns of zooplankton and walleye pollock (Theragra chalcogramma) off the Pacific coast of eastern Hokkaido, Japan, estimated by the volume back scattering strength (Sv) difference method

“…Walleye pollock have highly developed visual acuity (Zhang et al. , 1993) and feed during the day in both the Bering Sea (Yoshida, 1994) and Sea of Japan (Kooka et al. , 1997).…”

Metabolism and chemical composition of four pelagic amphipods in the Oyashio region, western subarctic Pacific Ocean

“…In terms of bathymetric distribution, T. pacifica and T. japonica are epipelagic, and P. abyssalis and C. challengeri are mesopelagic species (Yoo 1970, Wing 1976, Bowman 1978. These 4 amphipods have been reported as dietary components of salmon (Fukataki 1967, Tadokoro et al 1996, walleye pollock (Fujita et al 1995, Kooka et al 1997, Yamamura et al 2002, squid (Okiyama 1965) and mesopelagic fishes (Beamish et al 1999, Moku et al 2000, Uchikawa et al 2001, suggesting that they may have trophic importance in the pelagic ecosystems of this region. However, solid data for estimating the trophic functions, e.g.…”

Diets of walleye pollock Theragra chalcogramma in the Doto area, northern Japan: ontogenetic and seasonal variations

“…Due to their predominance, pollock has the potential to impact entire ecosystems (Springer 1992). Although numerous studies have been made on the feeding habits of postsettlement pollock (Takahashi & Yamaguchi 1972, Bailey & Dunn 1979, Clausen 1983, Maeda 1986, Dwyer et al 1987, Grover 1991, Yoshida 1994, Merati & Brodeur 1996, Kooka et al 1997, most of them covered only limited seasons and fish sizes. The studies made by Dwyer et al (1987) and Mito et al (1999) in the Bering Sea were exceptionally comprehensive describing geographical, seasonal and ontogenetic variations of pollock diet.…”