The authors estimate that between 17.9 and 39.5 million tons (average 27.0 million) of fish are discarded each year in commercial fisheries. These estimates are based on a review of over 800 papers. The highest quantities of discards are from the Northwest Pacific while tropical shrimp trawl fisheries generate a higher proportion of discards than any other fishery type, accounting for one third of the global total. Of four major gear groups, shrimp trawls stand alone at the top of the list; bottom trawls, long-lines and pot fisheries come next. The third group consists of Japanese high-seas drift net fisheries, Danish seines and purse seines for capelin. Relatively low levels result from pelagic trawls, small pelagic purse seines and some of high seas drift nets. The authors point to inadequate data to determine the biological, ecological, economic and cultural impacts of discards although economic losses run to billions of dollars. However, it appears most likely that socio-cultural attitudes towards marine resources will guide international discard policies. Techniques to reduce bycatch levels including traditional net selectivity, fishing gear development and time/area restrictions, are discussed. Effort reduction, incentive programmes and individual transferable quotas (that make the vessel responsible for bycatch reduction) are seen as promising avenues for the future. However, quick solutions to the problem are unlikely and much more information is required. The publication includes a diskette with the complete Bycatch Database, which was compiled for the study, and a summary of it.