Manual for the International Bottom Trawl Surveys. Revision IX.

Abstract

The International Bottom Trawl Survey (IBTS) in the North Sea has been conducted in the 1st quarter of the year since the beginning of the 1960s. The survey was first aimed at juvenile herring in the central and southern North Sea, but then the objectives of the survey were broadened to also provide recruitment indices for gadoids. The survey area was extended towards the northern North Sea and the Skagerrak/Kattegat in the 1980s. The full extent of the survey can be seen in Figure A1.1 in Annex 1. From 1991 to 1996, surveys were also conducted in the 2nd, 3rd, and 4th quarters, but since 1997, only the 1st and 3rd quarter surveys remained. The GOV trawl (chalut à Grande Ouverture Verticale) was introduced as the standard gear and the gear rigging and fishing method were standardized. However, some countries continued to use gears other than the GOV in the 3rd quarter IBTS until 1998.