Genetic problems of hatchery-reared progeny released into the wild, and how to deal with them

Abstract

Long-overdue concerns about the genetic effects of releases of hatchery-reared progeny on wild populations have been increasingly addressed during the past 20 yrs. Because of an extensive history of translocation and culture, much attention in both of these categories has focused on salmonid species. Native salmonids have been indirectly affected by translocations through such activities as induced overharvest in stock mixtures, disease introductions, and displacements resulting in fragmented populations with reduced numbers and, commonly, localized extinctions. Direct genetic effects through introgressive hybridizations of translocated salmonids have resulted in replacement of many native populations by hybrid swarms. Genetic effects from salmonid culture have led to losses of variability, both within the cultured populations and between the total cultured and wild populations, and to adaptive divergences distinguishing cultured and wild populations. Examples are provided that show that the overall salmonid experience is directly relevant to marine culture as well, although special considerations deal with the lower among-population diversity and greater fecundity often found in marine species. As marine enhancement programs inevitably expand, identifying and preserving natural populations are concerns common to harvest, management, and conservation interests. Coordinated rather than polarized approaches to these concerns best serve all parties as well as the irreplaceable resources.