Disentangling the contributions of ocean ranching and net-pen aquaculture in the successful establishment of Chinook salmon in a Patagonian basin

Abstract

The presence of Chinook salmon in Patagonia is an example of a successful invasion by a Pacific salmon species. The combination of historical records and genetic data can help to determine the origin of invasive / introduced species and allow the identification of the sources and dispersal process. We analyzed the genetic structure of Chinook salmon in the Futaleufú River (Pacific slope basin of Patagonia) using single nucleotide polymorphism genotypes and a recently described baseline dataset of native North American Chinook salmon populations. Our results revealed that Chinook salmon established in the Futaleufú River have high levels of within-population genetic diversity compared with populations from across the native range. Based on genetic similarity and historical reports, our results indicate that the Futaleufú population was first established by colonizing fish derived from the Lower Columbia River Basin, imported into Chile for ocean ranching purposes during the 1970s and 1980s, and afterward it was strongly supplemented by escaped fish from net pen aquaculture that used broodstock imported during the 1990s from various sources, including the California Central Valley (via New Zealand), the Middle Oregon Coast, and Vancouver Island. The higher incidence of fish derived from the most recent introductions in our sample suggest that the contribution of escaped salmon from these posterior stockings on establishment success must have been particularly strong because included different sources. Subsequent admixture and hybridization among these multiple independent source stocks is likely responsible for the high level of standing genetic variation, which may be facilitating local adaptation and augmenting the opportunity for successful invasion and further colonization.

Genomic patterns of diversity and divergence of two introduced salmonid species in Patagonia, South America

“…These genetic stocks correspond to a large extent to specific source populations that have been identified in a previous study with very dense representation of source collections (146 native populations from 46 genetic lineages; Correa & Moran, ). The other three collections of Chinook Salmon from North America allowed us to account for patterns of natural genomic variation as well as scenarios of colonization from multiple sources or possible admixture (Correa & Gross, ; Di Prinzio et al., ). Despite the first introduction attempts in the early 1900's, stocking history and genetic analyses indicate that current populations of Chinook Salmon originated from introductions in Chile for ocean ranching in the late 1970s and early 1980s primarily from the lower Columbia River (Cowlitz River Hatchery spring‐run; Correa & Gross, ; Di Prinzio et al., ).…”

“…The other three collections of Chinook Salmon from North America allowed us to account for patterns of natural genomic variation as well as scenarios of colonization from multiple sources or possible admixture (Correa & Gross, ; Di Prinzio et al., ). Despite the first introduction attempts in the early 1900's, stocking history and genetic analyses indicate that current populations of Chinook Salmon originated from introductions in Chile for ocean ranching in the late 1970s and early 1980s primarily from the lower Columbia River (Cowlitz River Hatchery spring‐run; Correa & Gross, ; Di Prinzio et al., ). In fact, this lineage prevails in our samples south of 43°S (i.e., Aysén and Baker; Correa & Moran, ).…”

“…This is consistent with reviews of studies of invasive species that genetic bottlenecks in founding populations are often overcome by propagule pressure (Dlugosch et al., ; Lockwood et al., ; Roman & Darling, ). In Chinook Salmon, genetic diversity of Patagonia stocks has probably been maintained by admixture or multiple colonization events from various stocks that escaped from ocean ranching (Di Prinzio et al., ). Given the significantly lower N b of Chinook Salmon that we observed in South America collections relative to native stocks, ongoing colonization events and admixture would explain how genetic diversity has been maintained.…”

“…These patterns of genetic structure are consistent with the hypothesis that distinct introductions coupled with connectivity and gene flow may be important for establishing populations on a broad geographic scale, consistent with reviews of introduced salmonids (Arismendi et al., ) and other invasive aquatic species (Roman & Darling, ). Once released or escaped from ocean aquaculture pens, anadromous Chinook Salmon have opportunities for colonization of multiple river systems with suitable habitat (Di Prinzio et al., ). Also, these anadromous fish returning from the ocean to freshwater may not always be philopatric, and thus, colonization of new areas may occur (Keefer & Caudill, ; Quinn, ).…”

Genetic signals of artificial and natural dispersal linked to colonization of South America by non‐native Chinook salmon (Oncorhynchus tshawytscha)

“…Past and recent genetics and genomics studies have identified multiple donor populations of Chinook salmon that likely interbred and now coexist among Pacific Ocean and Atlantic Ocean basins (Correa & Moran, ; Narum et al., ; Riva‐Rossi et al., ). Both individual assignment and genetic analysis of population mixtures (McKinney, Seeb, & Seeb, ) have greatly assisted tracking the geographic origin of donor Chinook salmon populations to various sites in South America (Ciancio et al., ; Correa & Moran, ; Di Prinzio et al., ). However, we lack a clear understanding on how genetic diversity, dispersal, and genetic admixture are linked to artificial and natural dispersal pathways of this species from its distributional range in South America.…”