COMPARISON OF SCALE AND OTOLITH AGE ESTIMATES FOR TWO SOUTH DAKOTA BLUEGILL POPULATIONS

Abstract

Bluegills Lepomis macrochirus were collected from Little Moreau Lake (Dewey County) and Lake Louise (Hand County) for a comparison of two different aging techniques. Bluegills were assigned an identification number, weighed, and measured. Scales were removed at the tip of the pectoral fin, below the lateral line, and sagittal otoliths were removed from each fish. Scales were aged by South Dakota Department of Game, Fish and Parks personnel, while otoliths were aged at South Dakota State University. The Little Moreau population sample (N=45) was dominated by young fish; 91% of the fish were ages 2-5 and only one exceeded age 6. Agreement between scale and otolith ages was very high; disagreements occurred for only five fish, and in all cases the age difference was one. The Lake Louise population sample (N=59) had a more extended age structure from 2-11, and 29% of the fish were age 6 and older. We found high agreement between scale and otolith age assignments for ages 2-5; only three disagreements occurred for these 32 fish. However, scale ages were consistently lower than otolith ages for age-6 and older fish. In addition, scale ages were as much as 5 years lower than otolith ages for these older fish. Thus, scales provided age assignments similar to those from otoliths over the first 5 years. However, scale ages were consistently underestimated for older bluegills when compared with otolith ages.