Sea-Run Brown Trout
The salmon that isn’t a salmon. Sea-Run Brown Trout (Salmo trutta) are one of the most widely distributed non-native fish introduced to Patagonia and Tierra del Fuego. They were first stocked in Tierra del Fuego by John Goodall in 1935. Shipped from Puerto Montt in Chile, 60,000 eggs survived the arduous journey and went on to be planted on the Candelaria and McLennan rivers, both tributaries of the Rio Grande. These fish eventually found their way to the sea, attracted by the rich food supply.
Today, sea-run brown trout complete a yearly migratory cycle just like Atlantic salmon and other salmonids that also spawn in freshwater. Sea-run browns remain in the river for a period of time that ranges from 1 to 4 years until their first ocean migration, where they will feed and grow for about 6 months before their first return to freshwater, weighing approximately 6 pounds. Researchers have found trout that have spawned as many as six or seven times. A sea-run brown that has completed 4 cycles of returning to freshwater can weigh more than 20 pounds. The regularity with which these trout return to freshwater indicates that the fish face few threats. Regardless, catch-and-release fishing still rules the day.
The Rio Grande sea-run brown trout are different. Mostly because they grow to unbelievable sizes. Average size varies but is usually over 7 pounds. Fifteen-pound fish are common and every week of the season 20-pound fish are released—yes every week. You have at least two chances in ten of catching a 20 pound fish every time you put a fly in the water. Our catch records go back to 1984 and these Browns are huge. That’s the simple truth.
Sea-run brown trout are not geese, and they were not necessarily born to migrate. The role of environmental factors versus genetics on the “decision” to migrate is still unknown. While genetics—and likely metabolism—could play an underlying role in the development of migratory populations, studies of other fish species fail to differentiate genetically between resident and migratory individuals within a population, and in fact indicate that interbreeding often occurs between the migratory and resident individuals. In some rivers they migrate, in others they don’t. That’s just the deal, but we are sure glad that the salmo trutta migrates on the Rio Grande and Rio Gallegos.