Ryderˈs morphoedaphic index (MEI: Total dissolved solids, TDS/mean lake depth) was developed empirically as a predictor of fish yield. It generally accounts for 60 to 78% of the variation (corrected sums of squares) in fish yields observed in a set of data. However, no basis for these correlations has been proven or even generally accepted. We demonstrate that two mundane relationships may be the reasons the MEI appears to be valid. Quite simply, large bodies of water tend to produce greater fish yields than small ones, and large bodies of water tend to have greater mean depths than small ones. Mean depth acts as a surrogate for surface area in the MEI; however, surface area alone is a more powerful predictor. It accounts for 94% of the variation in fish yields observed in three combined sets of data reported in the literature. The variation accounted for by the regression only increased to 95% when TDS was added as a predictor.

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This study addressed the question whether the increase in the abundance of striped bass Morone saxatilis in the Hudson River that began after 1990 and the associated increase in predatory demand could have been responsible for the observed declines in the abundance of juvenile river herring (i.e., blueback herring Alosa aestivalis and alewife A. pseudoharengus), Atlantic tomcod Microgadus tomcod, and white perch Morone americana as well as the apparent decline in the survival of juvenile striped bass in the Hudson River. The seasonal (August through October) predatory demand of Hudson River striped bass (ages 1‐13) was estimated to have increased from an average of 3.4 million kg/year for the period 1982‐1990 to an average of 15.0 million kg/year for the period 1991‐2004. Since 1990, the average abundance of juvenile fish in the Hudson River has declined—60% for river herring, 69% for Atlantic tomcod, and 59% for white perch—and juvenile striped bass survival has declined 87%. These declines could be explained by the increase in striped bass predatory demand if (1) 3.3% of the seasonal predatory demand of age‐1 to age‐13 striped bass was satisfied by consumption of juveniles of the four taxa or (2) 11.1% of the seasonal predatory demand of age‐1 and age‐2 Hudson River striped bass was satisfied by consumption of juveniles of the four taxa. Historical information on the fraction of the Hudson River striped bass stock that inhabits the Hudson River from August through October, combined with the dietary preferences of Hudson River striped bass, appear to be consistent with these levels of consumption.