The invasion of Patagonia by Chinook salmon (Oncorhynchus tshawytscha): inferences from mitochondrial DNA patterns.

The Chinook salmon Oncorhynchus tshawytscha, which was introduced deliberately in Chile four decades ago for sport fishing and aquaculture, represents a rare example of a successful translocation of an anadromous Pacific salmon into the southern Hemisphere, offering a unique opportunity to examine the role of introduction history and genetic variability in invasion success. We used historical information and mitochondrial displacement loop sequences (D-loop) from seven colonized sites in Chile and Argentina and from native and naturalized Chinook salmon populations to determine population sources and to examine levels of genetic diversity associated with the invasion. The analysis revealed that the Chinook salmon invasion in Patagonia originated from multiple population sources from northwestern North America and New Zealand, and admixed in the invaded range generating genetically diverse populations. Genetic analyses further indicated that the colonization of new populations ahead of the invasion front appear to have occurred by noncontiguous dispersal. Dispersal patterns coincided with ocean circulation patterns dominated by the West Wind Drift and the Cape Horn Currents. We conclude that admixture following multiple introductions, as well as long-distance dispersal events may have facilitated the successful invasion and rapid dispersal of Chinook salmon into Patagonia.