Greenland halibut observed by video in front of survey trawl: behaviour, escapement, and spatial pattern

Video recordings of Greenland halibut (Reinhardtius hippoglossoides) were made at eight trawl stations in Svalbard waters in August 2002. The recordings were made down to 600 m depth using artificial light. A method for calculating actual fish length from the video image was established and the recordings were analysed with respect to length-dependent behaviour, escapement and spatial pattern. All Greenland halibut observed were either lying on the bottom or swimming in a horizontal position close to the bottom, and there was no tendency to schooling. Individual fish reacted in an ordered way to the approaching trawl and were herded along the ends of the ground-gear. Escapement under the ground-gear was higher for smaller fish, while some larger individuals were apparently able to escape the trawl ahead of the observed region.