Life History Strategies
McIntyre River adult steelhead have a wide range of life history strategies for both stream and lake years. During their first one to three years, the juveniles reside in their home tributary prior to migrating (smolting) to Lake Superior (Figure 3).
McIntyre River steelhead spend one to four more years in Lake Superior prior to the onset of maturity and their initial spawning migration. After spawning, the surviving spent steelhead (kelts) return to the lake environment. A relatively high proportion of the adult steelhead are repeat spawners in successive years. In 2013, 52% of the males and 60% of the females had spawned more than once. Some males and females had spawned up to seven consecutive years.
Life history diversity is important to population stability (Moore 2013). Each year's spawning population has a variety of stream and lake year combinations at first spawn. If a year class fails to spawn successfully in one year, part of that year class still resides in the lake environment, maturing and migrating the following year or the year after.
An example of potential spawning failure was the spring of 2010 when drought conditions occurred in the Thunder Bay region. An entire year class could have been lost if all steelhead had matured at the same time. Strong year classes, such as 2007 and 2009 (Figure 2), contribute large numbers of adults to the spawning population for multiple seasons.
Steelhead growth is slow while in the stream environment and rapid once in Lake Superior. Figure 4 illustrates the average fork length of first-time spawning adult steelhead with two stream years at smolting. For a juvenile steelhead in the McIntyre River, the fork length is approximately 8 cm at age one, 16 cm at age two and >20 cm at age three. Once in the lake environment, steelhead grow rapidly reaching close to 35 cm after one lake year, 52 cm after two lake years, and 60 cm following three lake years. When steelhead reach maturity, linear grows slows considerably. This is due to weight loss during spawning (~40%), and the need to replenish gonads for the following years' spawning. Very large steelhead are often young and late maturing (after three to four lake years) with all their energy going into growth, rather than into gonad development. A 70 cm steelhead, therefore, may be a two-stream-years and four-lake-years maiden spawner. In turn, a 55 cm steelhead may be two-stream-years, five-lake-years, but on its fourth spawning run. The difference is the age at maturity.
