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WILLIS, MURPHY, AND GUY REVIEWS iN FISHERIES SCIENCE: we recommend that biologists use the proposed lengths rather than creating minor variations caused by "rounding." B. TRADITIONAL VS. INCREMENTAL RSD Gabelhouse (1984a) discussed two systems of RSD calculation: traditional and incremental. Traditional RSD values are calculated as the percentages of stock-length fish that also are longer than the defined minimum lengths for size categories. Thus, traditional RSDs are PSD [which actually is the relative stock density of quality-length fish (RSD-Q)], and relative stock density of preferred-length (RSD-P), memorable- length (RSD-M), and trophy-length (RSD-T) fish. Preferred length for largemouth bass is 38 cm; therefore, RSD-P is equivalent to the RSD-15 of Wege and Anderson (1978). Incremental RSDs determined the percentage of stock-length fish consisting of individuals between the minimum lengths for size categories. Thus, incremental RSDs are relative stock density of stock- to quality-length (RSD S-Q), quality- to preferred-length (RSD Q-P), preferred- to memorable-length (RSD P-M), memorable- to trophy-length (RSD M-T') fish, plus RSD-T. See Gabelhouse (1984a) for further information on the calculation of traditional and incremental RSDs. A common mistake in the reporting of stock density indices involves incremental RSDs. We remind biologists that S length is a minimum length, and includes all fish of that length and longer. Thus, RSD S-Q correctly identifies the percentage of stock- length fish that are from stock to quality length, not RSD of S fish. The latter actually infers all stock-length fish and is always equal to 100. Similarly, RSD-Q is the percentage of stock-length fish that also are longer than quality length; this is not equivalent to RSD Q-P (and is actually the same as PSD). When a biologist undertakes long-term monitoring of a single water body, the ability to recognize variable year-class strength is important. The use of incremental RSDs will allow the biologist to see the effects of strong or weak year classes on length-frequency data. Gabelhouse (1984a) suggested that traditional RSDs are best used for among-lake comparisons, such as an assessment of the relationship between population density and PSD, where lessening the effects of variable year- class strength would be helpful. In addition, we suggest that traditional RSDs would be more useful for one-time or first-time assessments of a particular fish population. Again, effects of variable year-class strength on stock density indices would be lessened, and comparison of the indices to desired objective ranges could be made. Ill. USE OF STOCK DENSITY INDICES As mentioned in Section I, 34 states and 1 Canadian province reported using PSD or RSD for at least 1 species in a 1985 survey (Gabelhouse et al., 1992). The most frequent use of PSD was for largemouth bass and bluegills (Table 1). This is not surprising because the indices were developed, and the first assessments were completed, for those species. For the warmwater species in Table 1, an average of 18 states and provinces used PSD or a similar index. Despite recommendations by Anderson and Weithman (1978) that PSD could be used for evaluation of coolwater 208