Steelhead abundance at age derived from fecundity and survival rates given by Quinn in his 2005 book
At the typical length in late summer for age 1 parr steelhead (about of 12 cm) or age 0 Chinook parr (about 9 cm), their preferred depth is roughly 0.8 m, which deeper than some pools and nearly all riffles. In fact, their changing preferences result in a progressive reduction in the area of riffles and pools that are suitable to them. This is strikingly evident from the depth frequencies of pools and rifles in typical steelhead streams spread across Oregon .
For example, a pair of steelhead defends a territory around their redd of roughly 5 m2 (??), spawn an average of 4,900 eggs (Quinn 2005), and an average 29% survive to be fry (Quinn 2005). This means that a spawning pair of steelhead produce about 711 fry, of which 355 survive to the end of the first summer, and 142 survive to age 1+ parr the second summer (Table 1). Even though the number of survivors in the cohort rapidly declines over time, the total area of suitable habitat required for territories of the surviving individuals increases with age of the cohort (Figure ). The surviving age 1+ parr require nearly five times the area than the fry, though five times more abundant, required. Given the large increase in habitat area required with increasing age, coupled with decreasing fraction of habitat that is suitable, it is likely that habitat availability will be most limiting at the oldest age that juveniles rear in freshwater.