Vertical distributions of walleye pollock Gadus chalcogrammus and euphausiids on the continental shelf of southern Okhotsk Sea, off the coast of Hokkaido, by using a quantitative echosounder
2019
Mizukami, T. (Hokkaido Government Kushiro General Subprefectual Bureau, Akkeshi, Hokkaido (Japan). Kushiro Fisheries Technical Guidance Office) | Itaya, K. | Mukai, T. | Iida, K.
To understand spring distribution patterns of walleye pollock Gadus chalcogrammus and euphausiids, we conducted an echo integration survey on the continental shelf region of the southern Okhotsk Sea at night in late April and June of 2012 and 2013. Walleye pollock aggregations were mainly distributed in the Soya warm current layer (SWC, >0 ℃, >33.5), that has a subsurface current of intermediate cold water (ICW, <0 ℃). In contrast, euphausiids were distributed at the surface layer of the ICW. In addition, we conducted a drift observation to observe diel vertical migration of euphausiids. Euphausiids were noted to descend to the lower layer of the SWC via the ICW before and after sunrise. Stomach contents of walleye pollock that were caught by bottom trawl consisted mainly of euphausiids, indicating that feeding occurs during euphausiids migration between the two current layers.
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