III.5 - Transportation validation

For the comparison a measure of river passage effects on transportation was computed using the equation

(174)

where

• T = total transport survival from transport dam. In this analysis T was set to 1 so the TBR measure does not include transportation effects
• S_{from transport dam} = model in river survival for fish from tailrace of transported to the estuary
• S_BON = model survival from Bonneville Dam tailrace to estuary.

(175)

Notice that the regression indicated that the estimated TBR underestimates observed TBR. Since the estimated TBR assumes a 100% transport survival factor the regression would suggest that actual fish survive better than predicted by the model. At the same time, note that the regression is very strongly affected by the outlier of 1973, where the observed TBR was over 16.

If we examine only the TBR below the mean of the estimated and observed TBR, both values are equal at 2.2. This additional information could be interpreted in one of several ways. The model could overestimate in-river survival in years with large TBRs or in years with large TBR the handling of the fish in the control groups produced additional mortality that was not represented in the model. In either scenario the fish transportation from model analysis and observations seems to produce survivals greater than could be obtained for in-river migration. Large TBR values are generally based on very small sample sizes and are therefore cannot be considered very robust. Fits for years with substantial recoveries are considerably better. Results of this analysis are preliminary and additional work will be conducted at a later date.

Fig. 83 Comparison of estimated and observed TBR for all species (chinook subyearling and yearling and steelhead) for years 1968 - 1987.