Replicating Otolith Ages for Largemouth Bass in Northern Lakes: A Comparison of Scales and Spines

Previous studies have suggested that otoliths provide the most accurate and precise estimates of largemouth bass age, but bass are not routinely sacrificed for removal of otoliths during standardized sampling in many states and provinces.  Scales are typically used as a nonlethal alternative to otoliths, even though many evaluations have suggested that scale-based age estimates may be inaccurate and imprecise.  Fin spines offer another nonlethal alternative to otoliths, but spines have not been thoroughly evaluated for largemouth bass and other centrarchids.  Our primary objective was to determine if anal and dorsal fin spines provide higher among-reader precision than scales and whether scale or spine ages are better for replicating otolith-based ages of largemouth bass in northern Wisconsin lakes.  Preliminary results indicate that dorsal spines are more precise than scales when compared to otoliths.  However, due to crowding of outer annuli and a large central lumen possibly obscuring at least one annulus, dorsal spines tend to underestimate ages for largemouth bass age 4 and older.