Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

Jack A. Stanford

Commitee Members

F. Richard Hauer, Lisa Eby


invasion, partial migration, Patagonia, Salmo trutta, sea trout


University of Montana


Brown trout (Salmo trutta) are widely introduced throughout Patagonia, though their distribution and impact in the region remain poorly documented. Life history flexibility, and particularly partial migration play a major role in the ability of this species to adapt to Patagonian rivers. Consequently, this study explored habitat, distribution and life history of a partially migratory population of brown trout in the Rio Grande in Tierra del Fuego, Argentina. It described what is known of the history of the invasion. Physical, chemical, and biological habitat data were collected for comparison between sites supporting resident fish with those supporting anadromous fish. Additionally, brown trout and native fish distribution and abundance was described using a combination of local knowledge, angling, electrofishing, and netting. Results indicate that brown trout developed an anadromous life history form several decades subsequent to their initial introduction, possibly after near extirpation of native galaxiid fish and reduction of invertebrate biomass. Sites supporting resident fish were narrower, and exhibited higher levels of specific conductance and soluble reactive phosphorous than those supporting both resident and anadromous fish. Resident sites additionally exhibited vastly higher invertebrate biomass. Significantly larger scale radii, suggesting faster juvenile growth was documented for fish in sites supporting resident fish versus those supporting anadromous fish, suggesting that food availability indeed may influence the individual ‘decision’ to migrate. The adult population proved to be exceptionally abundant and exhibited various life history traits which suggest that the Rio Grande supports one of the strongest remaining populations of anadromous brown trout worldwide.



© Copyright 2008 Sarah Louise O'Neal