Chinook salmon invade southern South America

Abstract

We document the invasion of Chinook salmon (Oncorhynchus tshawytscha) to southern South America providing historical, current and future perspectives. We conducted field sampling, angler surveys, and analyzed all written records, and found evidence of reproductive populations in more than ten Andean (and many more coastal) watersheds draining mainly to the Pacific Ocean in Chile (39°–53° S), but also to the Atlantic Ocean in Argentina (50° S). Invasion begun ∼25 years ago apparently from a few point sources of introduction by ocean ranching operations using spring-run Chinook salmon originated from tributaries of the lower Columbia River, USA. The rapid spread suggests that Chinook salmon were pre-adapted to their novel marine and freshwater environments because of similarities to equivalent North Pacific habitats, and invasion may have been facilitated by low ecological resistance. Preliminary data suggest that populations express a latitudinal gradient in juvenile migration life histories equivalent to that in their native range. Parallels to the only other establishment of anadromous Chinook salmon outside their native range, New Zealand, suggests a predictable invasion rate. In South America, the invasion is ongoing in southern areas, yet we deem unlikely colonization of rivers north of the range reached thus far. This is the first anadromous salmon species to have invaded such a large range in South America, and it raises many evolutionary, ecological, environmental and socioeconomic issues, with several discussed here.