Genetic resources and fisheries: policy aspects

The effects of fisheries on aquatic genetic resources are briefly reviewed. Fisheries impact on genetic resources at different levels and include selective fishing on stocks, genetic change in enhanced stocks, species extinctions, disruptions to ecosystems, and removal of nontarget species. Fishing exerts a selective force on natural populations by removing a restricted size range of individuals, so that traits linked with size and age are likely to be changed by selective fishing. The genetic impacts of fishing have been difficult to demonstrate in wild populations, due to the phenotypic plasticity of many life history traits that respond to both biological and physical parameters as well as selection pressures. Selection is likely to be fishery-specific and dependent upon the interaction between fishing gear and the average size and age at onset of sexual maturity of the target species. Measured genetic impacts in enhanced fisheries range from no detectable change to complete replacement of local stocks. Protocols have been developed that enable hatchery managers to minimize genetic change by careful choice of the origin and number of parents used for seed production. Species extinctions, and threatened and endangered aquatic species, are most common in freshwater and estuarine environments and are produced by habitat loss and degradation rather than direct impacts of fishing. However, marine fishes with low reproductive rates, large size at onset of sexual maturity, and restricted distributions, such as the collacanth and some sharks and rays, are vulnerable to exploitation. In addition, industrial fisheries are disrupting ecosystems. Many collapsed stocks have maintained relatively large population sizes and would not be expected to lose genetic diversity. Fishing also impacts on a range of nontarget species, and those with low population sizes and low reproductive rates, including sharks, turtles, albatrosses and marine mammals, are vulnerable to accidental harvesting. In many managed fisheries, measures are being put into place to reduce mortalities on nontarget species through gear restrictions and local closures. The move towards large-scale marine protected areas and seasonal closures will contribute to the conservation of nontarget species