Discards are the portion of a catch of fish which is not retained on board during commercial fishing operations and is returned, often dead or dying, to the sea. The practice of discarding is driven by economic and political factors; fish which are discarded are often unmarketable species, individuals which are below minimum landing sizes and catches of species which fishers are not allowed to land, for instance due to quota restrictions. Discards form part of the bycatch of a fishing operation, although bycatch includes marketable species caught unintentionally. Discarding can be highly variable in time and space as a consequence of changing economic, sociological, environmental and biological factors.[1]
Discarding patterns are influenced by catch compositions, which in turn are determined by environmental factors, such as recruitment of small fish into the fishery, and social factors, such as quota regulation, choice of fishing gear and fishers' behaviour. There have been numerous studies on the scale of discarding. In the North Sea the total annual quantity of discards has been estimated at 800,000–950,000 tonnes,[2] or the equivalent of one-third of the total weight landed annually and one-tenth of the estimated total biomass of fish in the North Sea.[3]