Nebraska Cooperative Fish & Wildlife Research Unit

 

Date of this Version

1997

Comments

Published in THE PRAIRIE NATURALIST 29:4 (December 1997).

Abstract

Variability in length-at-age estimates back-calculated from scales continues to be of concern 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 estimates 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 (Micropterus salmoides) at age 1 (P = 0.01), age 4 (P = 0.0001), and age 5 (P = 0.0001) and for walleyes (Stizostedion vitreum) at age 1 (P = 0.0001), age 2 (P = 0.0001), and age 3 (P = 0.0001). However, mean length-at-age estimates 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, transect use should be standardized when precise back-calculated length-atage estimates are needed.