ORIGIN AND GENETIC-STRUCTURE OF CHINOOK SALMON, ONCORHYNCHUS-TSHAWYTSCHA, TRANSPLANTED FROM CALIFORNIA TO NEW-ZEALAND - ALLOZYME AND MTDNA EVIDENCE

Chinook salmon, Oncorhynchus tshawytscha, transplanted from the Sacram ento River, California, to the Waitaki River catchment of New Zealand at the turn of the century rapidly colonized many South Island rivers. Allozyme genotype and mtDNA haplotype frequencies were obtained from tissue samples from chinook salmon in Waitaki, Rakaia, Waimakariri, an d Clutha rivers in New Zealand and compared with data from populations in the Sacramento River to provide further information on the origin of the NZ populations and to ascertain the genetic changes that have t aken place since the transplant. Neither allozyme nor mtDNA unequivoca lly identified an ancestral ''seasonal'' run (fall, winter, or spring) for the NZ chinook salmon. Sacramento River samples collectively dive rged from the NZ samples at allozyme loci, and mtDNA indicated greater similarity between NZ samples and fall-run rather than winter and spr ing runs from the Sacramento River. Significant variation was detected by mtDNA analysis between only two of the four populations within NZ, one of which has been landlocked by an impassable dam since 1956. The allozyme data identified significant variation within NZ, although le ss than has been documented among Sacramento River populations. The NZ populations also showed less genetic diversity (mean number of allele s per locus, proportion of loci that were polymorphic, and mean hetero zygosity) than the Sacramento River populations. These lower values ar e consistent with a population bottleneck in the first generations aft er transplantation into the Waitaki River catchment and with founder e ffects during the formation of populations in the other NZ rivers. The combination of genetic differences and phenotypic variation among the NZ populations indicates that Pacific salmon populations can develop rapidly after colonizing suitable habitat.