Brown trout (Salmo trutta) and sea trout (S. truttamorpha trutta) are both fish of the same species. They can be distinguished by the fact that resident, non-migrating browns live in freshwater river systems such as Chile’s Futaleufú, while the sea-run brown trout of Tierra del Fuego are anadromous, migrating to the ocean and returning to freshwater as massive salmon-size specimens to spawn.
Brown trout are native to Europe and Asia, but the natural distribution of the migratory forms may be circumpolar. Sea-run brown trout are not considered endangered in any location. But in some cases, individual stocks are under various degrees of stress due to habitat degradation and artificial (hatchery) propagation leading to introgression.
Brown trout like cold (60-65 degrees F, or 15-18 degrees C), well-oxygenated waters, especially large streams in mountainous areas. Cover is important, and they are more likely to be found where there are submerged rocks, undercut banks, and overhanging vegetation.
Browns in fresh water have the ability to grow to 9+ pounds. Although in most small rivers a mature brown might average 2 to 3 pounds. Tierra del Fuego’s sea-run browns are another story, and consistently push into the 20-30+ pound range. Fish this size are the ultimate prize.
Brown trout are active both by day and night and are predatory feeders. While in fresh water, diet can include small fish, frogs, and wayward mice as well as mayflies, stoneflies, caddis, and terrestrial insects. A brown’s unapologetic, all encompassing appetite is what makes it a fly-fishing favorite.