Midwater Trawling Studies in the North Pacific1

Abstract

A modified version of the Isaacs‐Kidd midwater trawl was used for 149 exploratory hauls in the Northeastern Pacific at depths ranging from 20 to 250 meters. Catches are discussed in terms of such factors as diurnal migration, seasonal variation, patchiness, and geographic variation.There was wide difference between day and night hauls. Geographic variation was marked. Abundance of plankton and fish decreased with increasing distance from the Washington coast, but increased again just south of the Alaskan peninsula. Northward and seaward there was a decrease in number of fish species. There appeared to be definite correlation between catches and an oceanographic boundary at approximately 50° North.A number of rare fish, one new species, and two leptocephalus larvae were taken.Consistency of results and close relationship of oceanographic and biological data suggest the usefulness of the midwater trawl as a valuable tool for future investigations of plankton ecology.