Natural Colonization and Establishment of a Chinook Salmon, Oncorhynchus tshawytscha, Population in the Santa Cruz River, an Atlantic Basin of Patagonia

Abstract

We report the finding of an established population of exotic Chinook salmon spawning in headwaters of the Santa Cruz River system (Argentina), the first for this species in an Atlantic basin of South America. Spawning takes place in the Caterina River, a small tributary of Lake Argentino, located 488.5 km from the ocean. Anadromy was verified by correspondence of N and C stable isotope ratios with those of fish captured by bottom-trawlers in the ocean and those of anadromous rainbow trout from the same river basin. The scale patterns of most fish examined were consistent with a stream-type life cycle (i.e., seaward migration by juveniles after a full year in fresh water). Two potential origins were identified for this population: in situ introductions of fish imported directly from the USA in the early 20th century or fish from two ranching experiments conducted in southern Chile during the 1980s. In the latter case, colonization would have proceeded through the Strait of Magellan, helped by prevailing eastward currents.