Proportionality of Body to Scale Growth: Validation of Two Back-Calculation Models with Individually Tagged and Recaptured Smallmouth Bass and Walleyes

Abstract

We compared the proportionality of scale to body growth and length estimates produced by the Fraser–Lee and Weisberg back-calculation models using individually tagged smallmouth bass Micropterus dolomieu and walleyes Stizostedion vitreum marked and recaptured in spring. Individual fish were tagged and later recaptured, providing multiple intervals of known growth to compare with back-calculated lengths (BCLs). There was no significant difference between total radii of scales collected when fish were younger and radii measured to the same annulus for scales collected from the same fish at final capture. Scale increment lengths remained constant and accrediting an annulus to the scale edge for fish caught in spring was valid. Known scale growth was not proportional to known body growth for smallmouth bass or walleyes; the body generally grew at a faster rate than the scales. Multiple regression analyses found that known scale growth described the most variance in known body growth, age was not always significant, and neither sex nor geographic location was ever significant. Fraser–Lee BCLs generally underestimated the actual lengths at tagging with errors ranging from −10 to +4% for both species. Weisberg BCLs were as accurate as Fraser–Lee estimates for older age groups but overall were less accurate, particularly for young fish (overall error range: −12 to +25%). The Fraser–Lee model is recommended for use over the Weisberg model because Fraser–Lee BCLs had lower overall range of error, Weisberg BCLs excessively overestimated lengths for age 1 fish, and the Weisberg model assumption of independence of successive scale increments within and between fish may not be valid.