San Francisco Estuary and Watershed Science

I previously estimated proportional losses of delta smelt to the water export facilities in the south Delta (Kimmerer 2008). This note is in response to Miller (2010), who disputes these estimated losses on several grounds. A re-analysis using a better analytical approach suggests a slight downward revision of the previous estimates for adult smelt. The distribution of smelt seems to have shifted northward in the last few years; if so, the delta smelt may now be less vulnerable to export losses than they previously were, although the reasons for such a shift are a concern. I argue, however, that it is legitimate to attempt such estimates in the absence of perfect information, and that mechanistic analyses are a valid way of estimating population-level impacts even in the absence of statistically significant correlations of estimated impact with subsequent population size.