An age-structured life-cycle model of steelhead (Oncorhynchus mykiss) for the Stillaguamish River in
Puget Sound, Washington, USA, was employed to estimate the number of age-1 steelhead parr that
could have produced the estimated adult return of 69 000 in 1895. We then divided the estimated parr
numbers by the estimated area of steelhead rearing habitat in the Stillaguamish River basin in 1895
and under current conditions to estimate density of rearing steelhead then and now. Scaled to estimates
of total wetted area of tributary and mainstem shallow shoreline habitat, our historic estimates
averaged 0.39–0.49 parr·m−2, and ranged from 0.24 to 0.7 parr·m−2. These values are significantly
greater than current densities in the Stillaguamish (mainstem average: 0.15 parr·m−2, tributaries:
0.07 parr·m−2), but well within the range of recent estimates of steelhead parr rearing densities in
high-quality habitats. Our results indicate that modest improvement in the capacity of mainstem
and tributary rearing habitat in Puget Sound rivers will yield large recovery benefits if realized in a
large proportion of the area of river basins currently accessible to steelhead.

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