Diurnal changes in bottom trawl catches and vertical fish distribution

Abstract

Bottom sampling trawl catches and acoustic abundance estimates of North-East Arctic cod and haddock in the Barents Sea were collected and examined according to time of day. The trawl catches were at average larger by day than by night, and there was a larger proportion of small fish ( <40 cm) in the night catches. The acoustic recordings showed a considerable diurnal vertical migration of cod and haddock. The fish seemed to stay close to bottom by night and lift off from bottom by day. Aggregations of haddock were observed up to about 150 m above bottom at daytime. Fish density in the bottom layer as estimated from trawl catches agreed closely to echo abundance by night. At daytime no correlation was found.