The Santa Cruz River Steelhead

The Santa Cruz River (50ºS, 72ºW) is the second largest river in Argentinean Patagonia. The upper basin is dominated by two large glacier-fed lakes, Viedma and Argentino, connected by the La Leona River, the second most important river of the drainage system after the Santa Cruz. From its source, along the Andean Cordillera, the river flows east for 382 km across the Patagonian plateau to drain into the Atlantic Ocean with and average gradient of 0.53m/km. The Santa Cruz is a glacier-fed river with an average annual discharge of 690m3/s, with maximum in late summer due to glacial melt water input (2000 m3/seg), and minimum in the spring (150m3/s).

The Santa Cruz is joined by its most important tributary the Bote River about 26 km downstream from its source, at a reach known as “Vuelta del 2º Laberinto” where the river takes a sharp turn to the west producing a large meander. The river then meanders east to the “Vuelta del 1º Laberinto” where it turns to the south flowing across a wide valley with substantial gravel bars that offer abundant riffle and groundwater-fed pool habitat.

Downstream from this section, the Santa Cruz is joined only by small, intermittent tributaries such as Lechuza, Yaten Guajen and Kolian Kaike creeks. In the middle portion, the river channel narrows down, flowing with a meandering course before entering a series of rapids (rápidos???). In the lower reaches, the river widens out to a main channel of about 700m and becomes tidal, with islands and large bars at Isla Pavón (40 km from the ocean). The river flows into the Atlantic Ocean through a 25km long estuary (6km in widest section). The flow in the lower reaches reverses during high tide (tidal amplitude of 8 m), with effects propagating as far upstream as 57 km. At the estuary, the Santa Cruz is joined by the Chico River.

After hatching, juvenile Santa Cruz River steelhead remain in freshwater for two or three years; then descend to the ocean to feed and grow for at least a year before returning to freshwater. The run starts in the fall but spawning does not occur until spring. Most individuals spawn for the first time during their second river entry from the ocean. A typical Santa Cruz steelhead repeats these migrations between feeding and breeding grounds several times throughout their life time and as many as eight times, with fish growing as old as 11 years.

El Chinook salmon from the Caterina River, upper Santa Cruz River Basin

The Caterina River is a glacier-fed river with an average discharge of 21.4 m3/seg, It is located within Estancia Cristina (49ºS, 73ºW) in Los Glaciares National Park and flows south for 7.72 km between glacier-fed Lake Anita (666 m elevation) and Lake Argentino (580 m elevation). It has only two small, high gradient tributaries, “de las Frutillas” and “de los Perros” creeks. The average gradient of the Caterina River is 11.13 m/km, with a 2 km fast flowing upper section and a 6 km middle section with moderate flow and smaller gravel sizes (10 –100 mm diameter). At the lower section the river widens out towards the mouth to drain into Lake Argentino.

The sea-run brown trout from Gallegos (Santa Cruz) and Grande (Tierra del Fuego) Rivers

The Gallegos River (51°S, 72°W) is the southernmost Atlantic drainage system of continental Patagonia. It flows for 300 km across the Patagonian plateau from it sources in the Southern Andes to drain into the Atlantic Ocean through a 30 km long estuary. The main channel of this river originates in the Turbio River, which after its confluence with the Condor creek, tributary of Lake Condor, changes its name to Gallegos.

The upper Gallegos is joined by the Zurdo and Penitentes rivers as it flows east across a narrow, meandering channel. In the middle and lower sections, the main channel widens and flattens out receiving few intermittent streams such as the Gallegos Chico River.

The Grande River (53ºS 68ºW) is the major drainage system of Tierra del Fuego Province, extending for 170 km across an area covered by a mosaic of wetlands, marshes, ponds, and watercourses from Chile and Argentina. The Grande has its sources in Chile, on the north-east facing-slopes of the Fuegian Andes, in small streams that feed its two main sources the Donoso and Rusphen Rivers. In its western upriver section into Chile, the Grande is joined by several small and intermittent tributaries as it meanders eastward across narrow valleys.

In its eastern, Argentinean section, the Grande widens out and flows east meandering across alluvial, sometimes wide, valleys, and is joined by the Herminita, Bella Vista and Menendez rivers. In the lower section, the main channel narrows down and is joined by the Candelaria River from the south. The river then widens out again, forming a large estuary that drains into the Atlantic Ocean. Lowest discharges occur during winter and highest during summer, flooding the lower reaches. 

There is little information about the life cycle of the sea-run brown trout of the Gallegos and Grande rivers; based on preliminary scale pattern analysis, the life cycle appears to be somewhat similar to that of Santa Cruz River steelhead. Young fish remain between 1 and 4 years in fresh water, and between 1 to > 2 years in the ocean before returning to freshwater to reproduce for the first time. Adult individuals may spawn for the first time during their first or second river entry. They repeat migrations to and from the ocean for as many as 6 times. In this species the run extends between November and April (spring to fall in the Southern Hemisphere), with spawning beginning in April.