Skreitelling med ekkointegrator i Lofoten i 1972

Abstract

A survey in the inner part of the Lofoten area was carried out vith R.V. «Johan Hjort» 14-15 March 1972. Abundance estimates and distribution charts were made on the basis of echo integrator deflections. The abundance estimates were low compared with those from 1971, probably because more of the cod occurred in shallow waters out of reach from the echo sounder in 1972 than in 1971. Inside an area the abundance of cod was found to be much higher by day than by night. The difference was probably due to migration of the cod. Integration of echoes from the bottom in areas where the slopes were steep caused severe difficulties, and this problem will have to be solved in order to make the abundance estimates more accurate. The cod is probably never distributed in a way that makes covering of the total spawning stock during one survey possible. The distribution of the cod therefore probably causes the biggest problem in abundance estimation of the total spawning stock.