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Volume 1 (Issue #3), 1993 STOCK DENSITY INDICES <br />value. "Quality" length was defined by Anderson (1978). PSD is quite similar to the <br />AT value suggested by Swingle (1950). The primary difference between the two <br />indices lies in the fact that PSD is calculated from numbers of fish, whereas AT is <br />determined by weight. <br />Stock and quality lengths were first proposed for warmwater fishes such as <br />largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). Anderson <br />and Weithman (1978) defined stock and quality length as percentages of world- <br />record fish lengths, and also recommended application to coolwater fishes such as <br />yellow perch (Perca flavescens), walleye (Stizostedion vitreum), smallmouth bass <br />(M. dolomieu), northern pike (Esox lucius), and muskellunge (E. masquinongy). The <br />percentage ranges were based on a fish quality index developed by Weithman <br />(1978; Figure 1). Stock length was the point at which the fish quality index came <br />off the x-axis, and thus represents the point where a fish first has any recreational <br />value to the angler. Quality length was the inflection point at which the fish quality <br />index starts to climb steeply. <br />Trophy <br /> <br />3.0 <br />Preferred <br />I <br />~~~ <br />Memorable <br />I ~ <br />i i <br />i i i i <br />~ ~ ~ I <br />w <br />J <br />F- <br />Z <br />a 2.0~ <br />D <br />oC <br />z <br />,.0 <br />QUaI%ty <br />Stock <br />i, <br />~~ <br />~~ <br />~_ <br />~~ <br />~~ <br />~~ <br />~~ <br />,~ <br />0 20 40 60 80 <br />WORLD-RECORD LENGTH (%) <br />FIGURE 1. Weithman's fish quality relationship adopted by Gabelhouse to identify length ranges for his <br />five-cell length-categorization system. The dashed lines indicate the ranges from or near which <br />minimum stock, quality, preferred, memorable, and trophy lengths should be chosen. (Adapted from <br />Gabelhouse, 1984a.) <br />205 <br />