Decline in Natural Fisheries — A Genetic Analysis and Suggestion for Recovery

Abstract

Overfishing and pollution of the aquatic environment, in addition to their direct effects on natural fisheries, may have also influenced natural fish populations genetically. Overfishing drastically reduces population size and, since the larger individuals are selectively removed, is equivalent to selection for smaller sized fish. Adaptation of natural fish populations to their environment must have been reduced by rapid environmental changes resulting from pollution and infestation. Inbreeding, negative selection, and lack of adaption are here considered as the genetic causes for the decline of natural fisheries and lack of recovery. Restocking programs involving hatchery stocks are unlikely to solve this problem, since these stocks were selected for adaptation to hatchery environments and not to natural environments. A series of studies have demonstrated heterosis of interstrain crossbreds, mainly between hatchery and wild stocks of salmonids, for performance in natural waters. Two strategies could be implemented in restocking programs: stocking spawners of a domestic strain (preferably of one sex) for interbreeding with the resident population or direct stocking of crossbred fry. This should be tested in small isolated bodies of water and needs to be accompanied by a monitoring program in order to evaluate the results and minimize hazards.