(English) Muskellunge scale interpretation: The questions of aging accuracy

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Age and growth data extracted from scales are often used when managing fish populations. However, accurate interpretation of scale annuli in certain species, such as muskellunge Esox masquinongy , has been suspect. The accuracy of age determination was tested with three experienced esocid scale readers who interpreted positive photo images made from acetate slide impressions projected on a microfiche reader. Images were made from scales of 25 known‐age muskellunge (3–10 years old) from five Wisconsin lakes. Each scale image was interpreted twice; once with fish length, sex, and date of capture given and once without any information. Of 149 scale interpretations, 32% were assessed with the correct age, 54% underaged, and 14% overaged. The average interpretation deviated from the known age by 1.0 years. Accuracy did not improve when additional fish information was available. General confidence in the interpreter’s age assessments was low and possibly related to quality of the photo images. Interpreters were accustomed to using acetate images with several impressions rather than a single photo image. As a follow‐up, we selected 12 acetate slides used to make the photo images and allowed each interpreter to determine age from the slides. The percentage correctly aged with the subsample improved from 24% to 47% with the acetate slide impressions. Increasing the magnification of acetate slides from 23× to 35× magnification did not affect accuracy. Image quality and multiple impressions can improve accuracy of age determination; however, accuracy was still less than 50%. The low accuracy when interpreting scale annuli of muskellunge 3–10 years of age suggests that managers need to use caution when evaluating data taken from muskellunge scales.