A Comparison of Methods for Estimating Ages of Unexploited Walleyes

Abstract

Age estimation is an important diagnostic tool for fisheries managers. Previous studies on comparison of age estimation methods of walleyes Stizostedion vitreum have shown otoliths are the best method overall and that dorsal spine cross sections are a suitable alternative to scales, the most commonly used method. We compared ages estimated from scales, dorsal-spine cross sections, and otoliths for unexploited walleyes from Pymatuning Sanctuary, Pennsylvania. We collected these structures from fish sampled in trap nets during the spawning run in March and April 1997. Two readers independently examined these structures without knowledge of fish length or gender. Otoliths provided the best agreement between readers for both genders (94% for females, 86% for males) and dorsal-spine cross sections provided the poorest agreement (63% of females, 62% of males). Younger ages were estimated from scales than from spines, and this difference was greater for males than for females. Age estimates from both scales and dorsal spines agreed poorly with age estimates from otoliths for both sexes. Ages estimated from scales were consistently lower than ages estimated from otoliths, especially after age 4; differences between ages estimated from otoliths versus spines were inconsistent. We concluded that otoliths are the best method of age estimation for this population and that scales are the best alternative for fish less than 500 mm long. This research underscores the need to validate age estimates with fish of known age and to test multiple age estimation methods when beginning research on previously unstudied populations.