Fishing, selection, and phenotypic evolution

Large changes are taking place in yield-determining traits of commercially exploited fish, including traits such as size-at-age and age-at-maturation. The cause of these phenotypic changes is often not understood, and genetic change arising from the selective effects of fishing may be a contributory factor. Selection generated by fishing gear is strong in heavily exploited fish stocks, and the spatial location of fishing can also cause strong sel ection. The success of selective breeding in aquaculture indicates that sig nificant amounts of genetic variation for production-related traits exist i n fish populations. Fisheries managers should be alert to the evolutionary change caused by fishing, because such changes are likely to be hard to rev erse and, if properly controlled, could bring about an evolutionary gain in yield. (C) 2000 International Council for the Exploration of the Sea.