Discards of the French trawler fleet operating in the Celtic Sea in 1997 were studied. Twenty-six trips, representing 0.8% of the total fishing effort, were sampled. This fleet consists of three métiers, benthic trawlers, Gadoid trawlers and Nephrops trawlers. The fleet discarded an estimated 30 000 tons of animals in 1997, while landing 63 000 tons. The total quantity discarded did not differ among métiers, but the species composition of discards did. Benthic trawlers discarded mainly by-catch species, whereas Gadoid and Nephrops trawlers discarded primarily their target species. Whiting, megrim, Nephrops and hake were discarded in larger numbers than landed. Hence discards should be taken into account in catch-based assessments. However, discards were found to be highly variable between trips and between years. In addition, no reliable auxiliary variable could be found when various factors were investigated to explain the quantities of commercial species discarded. The only explanatory factor valid for any species was the smallest size of that species in the catch. Hence there is a need for regular sampling of discards. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved .