Bocking et al. 2005

Bocking, R. C., C. K. Parken, and D. Y. Atagi. 2005. Nass river steelhead habitat capability production model and preliminary escapement goals. Ministry of Water, Land and Air Protection, Skeena Fisheries Report # SK 142, Smithers, British Columbia, Canada.

This report describes a habitat-based steelhead production model for the Nass watershed and presents the results for 63 sub-basin watersheds of 3rd order size or greater (1:20,000 mapping). The primary objective was to develop a habitat-based method for estimating smolt production capacity and spawning potential of Nass River tributary streams based on watershed features, physical habitat data, and biological production parameters. The model predicts the amount of suitable habitat available to support juvenile (fry) steelhead for rearing and converts these habitat estimates into production estimates for smolts and minimum escapement levels required to fully seed the available habitat. The watersheds studied include 26 winter steelhead populations systems, 34 summer population systems, and two sympatric systems. The model was run for accessible area of 4th order or larger streams (4th order model) as well as for 3rd order or larger streams (3rd order model). Six different models were used to
estimate the number of smolts at stream carrying capacity (based on the amount of useable length or area for fry). Three of the models used carrying capacity estimates of smolt production for the Keogh River, on northern Vancouver Island; and three used carrying capacity estimates of smolt production for the Cranberry River, a Nass summer run steelhead tributary. Including just 4th order or larger tributaries, smolt production estimates for all confirmed steelhead habitat in the winter population systems ranged from 17,774 to 55,266 for the six different models. Smolt production estimates for all confirmed habitats for the sympatric populations ranged from 2,759 to 9,891. Smolt production estimates for all confirmed habitats
for the summer populations ranged from 86,417 to 248,272. Using the Model 6 smolt production estimate (Adjusted Areas Model), and only
including tributaries for which steelhead are known to be present, the required number of winter run spawners to fully seed fry habitat in the lower Nass River tributaries was estimated to be 1,204. For the sympatric populations, the required number of spawners was estimated to be 310.
The estimated required number of spawners for the summer populations with confirmed steelhead presence was 12,386 which is within the range of recent mark-recapture estimates of this aggregate of summer stocks for the period 1997-2001. The model was particularly sensitive to alkalinity, mean smolt age, and egg-to-fry survival estimates.