Back-Calculated Length-At-Age Estimates from Two Scale Radii

Variability in length-at-age estimates back-calculated from scales continues to be of concem to fishery scientists. Measurement transects used to back-calculate length at age have been recommended; however, specific scale and annuli radius measurements have not been evaluated for variability between different radii. Thus, the purpose of our study was to compare back-calculated length-at-age eslimates determined from two different scale radii: one horizontally from the focus to the anterior-median edge and one diagonally from the focus to the anterior-lateral corner of the scale. No significant differences (P = 0.13 0.58 and P = 0.24 0'87) in backcalculated length-at-age estimates between the two transects were found for black crappies (Pomoxis nigromaculatus) and bluegills (Lepomis macrochirus), respectively. Statistical differences between back-calculated length-at-age estimates determined from the two transects were found for largemouth bass (Micro$erus sa/morUes) at age 1 (P = 0.01), age 4 (P = 0.0001)' and age 5 (P = 0.0001) and forwalleyes (Stizostedionvitreum) at age 1 (P = 0.0001)' age 2 (P = O.00Ol), and age 3 (P = 0.0001). However, mean length-at-age esiimates for largemouth bass and walleye samples differed little (0'1-6'3 mm). The small differences in mean back-calculated length-at-age estimates between these transects should not affect growth assessments. However, transed use should be standardized when precise back-calculated length-atage estimates are needed.