Distribution and Movement of Walleye Pollock Larvae Theragra chalcogramma in Funka Bay and the Adjacent Waters, Hokkaido

Abstract

In order to elucidate the distribution and movement of walleye pollock larvae Theragra chalco-gramma, samplings were conducted in Funka Bay and the adjacent waters from April 1978 to November 1982. From April to June, larvae were found mostly in the surface and subsurface layer of the bay. In July the larvae were concentrated on the sea bottom(100m depth) of the bay and in August a part of them were found on the deep sea bottom (300m depth) in the eastern area outside the bay.
From April fo July, the surface water temperature in the bay rose from 4°to 18°C, while the bottom water temperature remained unchanged (3°-6°C). As growth proceeds, the main foodorganisms of the larvae changed from Pseudocalanus minutus to the larger copepodids of Calanus plumchrus and Eucalanus bungii bungii, euphausiids Euphausia pacifzca, and amphipods Parathzmisto japonica. P. minutus dominated in the surface layer of the bay from March to April, decreased remarkably after May. In contrast, the larger copepodids of other copepods increased in deeper layer after June. It was considered that the vertical movement of the larvae with growth wasclosely associated with the suitable temperature condition and food availability.