GENETIC IMPACT OF ESCAPED FARMED ATLANTIC SALMON (SALMO-SALAR L.) ON NATIVE POPULATIONS - USE OF DNA PROFILING TO ASSESS FRESH-WATER PERFORMANCE OF WILD, FARMED, AND HYBRID PROGENY IN A NATURAL RIVER ENVIRONMENT

Since Atlantic salmon (Salmo salar L.) used for farming are usually ge netically different from local wild populations, breeding of escaped f armed salmon potentially results in generic changes in wild population s. To determine the likelihood and impact of such genetic change, an e xperiment was undertaken, in a natural spawning tributary of the Burri shoole system in western Ireland, to compare the performance of wild, farmed, and hybrid Atlantic salmon progeny. Juveniles were assigned to family and group parentage by DNA profiling based on composite genoty pes at seven minisatellite loci. Survival of the progeny of farmed sal mon to the smelt stage was significantly lower than that of wild salmo n, with increased mortality being greatest in the period from the eyed egg to the first summer. However, progeny of farmed salmon grew faste st and competitively displaced the smaller native fish downstream. The offspring of farmed salmon showed a reduced incidence of male parr ma turity compared with native fish. The latter also showed a greater ten dency to migrate as autumn pre-smelts, Growth and performance of hybri ds were generally either intermediate or not significantly different f rom the wild fish. The demonstration that farmed and hybrid progeny ca n survive in the wild to the smelt stage, taken together with unpublis hed data that show that these smelts can survive at sea and home to th eir river of origin, indicates that escaped farmed salmon can produce long-term genetic changes in natural populations. These changes affect both single-locus and high-heritability quantitative traits, e.g. gro wth, sea age of maturity. While some of these changes may be advantage ous from an angling management perspective, they are likely, in specif ic circumstances, to reduce population fitness and productivity. Full assessment of these changes will require details of marine survival, h oming and reproductive performance of the adults together with informa tion on the F-2 generation. (C) 1997 International Council for the Exp loration of the Sea.