Validity of age estimates from muskellunge (Esox masquinongy) fin rays and associated effects on estimates of growth

Abstract

Accurate age estimates are critical for understanding life histories of fishes and developing management strategies for fish populations. However, validation of age estimates requires known-age fish, which are often lacking. We used known-age (ages 1–25) muskellunge (Esox masquinongy) to determine the precision and accuracy of age estimates from fin rays. We also determined whether fin location (anal or pelvic), fin ray number, and preparation methods affected accuracy and precision. Lastly, we determined whether von Bertalanffy growth parameters estimated from fin ray ages were similar to parameters estimated from known ages. Precision and accuracy of age estimates from anal and pelvic rays were similar and estimates were relatively precise (coefficient of variation = 8.5%) and accurate (mean absolute difference from known age = 0.85 years) for ages 4–15, but ages were overestimated for younger fish and underestimated for older fish. Growth models based on estimated age were similar to models based on known age. Anal and pelvic rays offer a nonlethal alternative for age estimation of muskellunge ages 4–15 and for producing reliable estimates of growth.

Accuracy of Concert versus Independent Age Estimates Made from Anal Fin Rays of Muskellunge

“…The first three to four anal fin rays were cut at the base of the fin (proximal to the body) using diagonal cutters, allowed to air dry, and then cleaned of tissue. Accuracy of Muskellunge age estimates derived from the third and fourth anal rays is similar (Crane et. al 2020).…”

“…Anal fin rays were collected from Muskellunge in Illinois, Iowa, Kentucky, Wisconsin, and Virginia during spring broodstock collections and population surveys. Known age was determined by unique marks or tags (fin clips, vinyl anchor tags, freeze brands, or PIT tags) applied to fish prior to stocking (Crane et al 2020). The first three to four anal fin rays were cut at the base of the fin (proximal to the body) using diagonal cutters, allowed to air dry, and then cleaned of tissue.…”

“…Because sacrificing Muskellunge for age estimation does not align with common management objectives for this species, use of fin rays for age estimation has increased in popularity. Crane et al (2020) examined the accuracy, precision, and bias of Muskellunge age estimates (based on independent age estimates from three readers) derived from anal and pelvic fins. They found that ages estimated from anal fin rays were unbiased and relatively accurate (mean absolute difference from known age <1 year) and precise (coefficient of variation <10%) for fish ages 4-15, but estimates for younger (<4) and older fish (>15) were biased and less accurate and precise (Crane et al 2020).…”

“…Crane et al (2020) examined the accuracy, precision, and bias of Muskellunge age estimates (based on independent age estimates from three readers) derived from anal and pelvic fins. They found that ages estimated from anal fin rays were unbiased and relatively accurate (mean absolute difference from known age <1 year) and precise (coefficient of variation <10%) for fish ages 4-15, but estimates for younger (<4) and older fish (>15) were biased and less accurate and precise (Crane et al 2020). Because Crane et al (2020) only used independent age estimates, we investigated whether concert readings of anal fin rays increased accuracy and decreased bias of age estimates when independent reader estimates disagreed.…”

“…They found that ages estimated from anal fin rays were unbiased and relatively accurate (mean absolute difference from known age <1 year) and precise (coefficient of variation <10%) for fish ages 4-15, but estimates for younger (<4) and older fish (>15) were biased and less accurate and precise (Crane et al 2020). Because Crane et al (2020) only used independent age estimates, we investigated whether concert readings of anal fin rays increased accuracy and decreased bias of age estimates when independent reader estimates disagreed. Additionally, because Buckmeier (2002) and Buckmeier et al (2002) observed that concert estimates increased accuracy and decreased bias for Largemouth Bass and Channel Catfish, we compared independent and concert estimates for all samples, regardless of whether reader estimates disagreed, to determine if readers should forgo independent estimates, only conduct concert estimates, and use differences between reader pairs to estimate precision.…”