Skagit Bull Trout Primer Ch 1: The Early Years

In the North Cascades it is winter. On a Skagit basin stream located above 2,000 feet elevation, the forest floor and stream banks have been snow covered for months and the water itself stands just barely above freezing. The clean and stable gravel in this wilderness stream and the other moderate to small waters like it provide near ideal environments for the eggs and young fry of one of the Pacific Northwest’s enigmatic species. With the stirring of life in those gravels the next generation of our native char, the bull trout, prepare to hatch. As the fry wriggles out of the gravel the life story of one of the most diverse and interesting Skagit salmonids begins. This complex life story is part of what endears this fish to so many of its fans.


Photo @Matt B

The expression of some of that diversity (behaviors and life histories) begins also immediately as the fry emerges. In streams where the bull trout are the only fish species in the stream, a careful observer can see those tiny fry darting in the shallows, holding in the eddies, darting in and out of the root wads, etc. However, in streams where the bull trout share the water with other fish species; typically, O. Mykiss (either resident rainbows or steelhead) and in some cases Chinook/coho salmon can also be present, the bull trout fry and parr are not to be found during the daylight period. They instead bury in the gravel, hide in the rod wads and log jams, etc. only to emerge during the hours of darkness. A behavior that perhaps is an adaptation to avoid interactions with the other fish.

It often is the case that the numbers of fry emerging from the gravel exceeds the capacity of the habitat to support for extended rearing. As a result, only a portion of those new fry remain to mature and eventually to spawn in or near their natal stream. With our human need to have things in nice, neat boxes we label these stay-at-home bull trout as having the resident life history. They will reside here, taking 4 to 5 years to reach maturity. The first-time resident spawners average about 8 to 10 inches in length.

The fry/parr that do not find a home in the headwaters move downstream to find suitable habitats for additional rearing and growth. As they enter their third year at about 6 inches they will have established four unique life histories. Those that have found a home in large lake systems are placed in the adfluvial life history. In the Skagit basin the upper Baker and upper Skagit reservoirs are such habitats used by these bull trout. While these fish are interesting in themselves, they are not often encountered by anglers fishing the main stem Skagit. The focus for the remainder of this article will be on the other three life histories; the resident, fluvial and anadromous histories.


Photo @MarshRat

The parr, now 6-inch fish, are destined to be placed in the fluvial or anadromous box but up to this point have shared common rearing strategies. While largely invisible to the observer since leaving the headwaters they have moved downstream to progressively larger waters though some will explore side tributaries. During that first year they typically reside in slower velocities water found along the margins of the riffles, runs and pocket water. During this early rearing their diet consists of primarily insects and smaller food items. Over the next year or so as they grow larger, pool habitats become more important and the bull trout’s diet expands to include larger prey items with various fish species appearing on the menu. Common fish prey includes sculpins, whitefish, lamprey, and various salmonids. At this stage, about age 2, that the fluvial and anadromous life histories separate. The fluvial fish become even more strongly associated with the larger pools throughout the basin. Over the next two years, thanks to more abundant food resources these fluvial fish will grow to 15 to 17 inches in length as they reach sexual maturity.

In the spring at the start of that third year the bull trout destined to adopt the anadromous life history become smolts (undergo physiological changes to allow the transition from a freshwater environment to a marine one). They make the move to marine waters in late April, May and early June. Many of these fish move pretty quickly to the bay, though some spend extended time in the tidally influenced reach. In this new habitat various fish species become the dominant forage. In the north sound marine environment smelt are the most common forage with other important fish being shiner perch, herring, sand lance, sculpins, juvenile salmonids, and just about any other fish they can catch and swallow. Much like their distant cousin the sea-run cutthroat, once in the salt they spend much of their time along the shoreline in relatively shallow waters (though the bull trout tend to travel further from their home river). Radio tagged Skagit fish have been tracked as far south as Seattle and the Duwamish River. An interesting twist with this anadromous life history is after summer in the salt, much like the basin’s sea-run cutthroat, they return to freshwater to over-winter. This reverse migration starts in late August and is largely completed by November. By this time those 6-inch smolts have grown to 10 to 12 inches in length. While most of the fish return to the Skagit some will spend time in other nearby systems. These fish typically over-winter in the lower 20 to 30 miles of the river, returning to the salt in the late winter/early spring often having grown another coupe inches. Once back in the salt the fish feed heavily growing quickly. After several months the maturing fish (having grown to 18 to 20 in length) begin their first trek to the spawning grounds. Those migrating fish move quickly. For example, radio tagged fish holding off the mouth of the Snohomish for months can suddenly migrate north along the shoreline to the mouth of the Stillaguamish, across to Camano Island, around the west side of Camano, across Skagit Bay and into the river in as little as 36 hours. At least initially that quick migration continues once they reach the river.


Skagit river photo @kerrys