Comparison of Four Hard Structures Including Otoliths for Estimating Age in Blue Suckers

The Blue Sucker Cycleptus elongatus is an imperiled North American catostomid in need of management and protection. No hard structures are validated for aging this species, but past studies focused on somatic structures such as fin rays and scales. Calculated parameters (mortality, recruitment, growth) that inform management decisions are directly influenced by the accuracy and precision of the hard structure used to estimate age. We identify the most precise and credible structure with which to age Blue Suckers while also completing the first in-depth investigation of their otoliths. We collected Blue Suckers (n = 168) from the lower Wabash River and compared ages estimated from scales, opercles, pectoral fin rays, and lapillus otoliths but were unsuccessful in estimating ages from cleithra. We identified structure bias between all structures and found scales (n = 67; maximum = 11 years, mean = 8.2 years) and opercles (n = 65; maximum = 15 years, mean = 8.3 years) to be substantially less precise than pectoral fin rays and lapillus otoliths. We found that otoliths (n = 128; maximum = 42 years, mean = 13.5 years) were more precise than fin rays (n = 167; maximum = 20 years, mean = 9.6 years) and yielded a much higher range of ages. We could not identify any range of ages or total lengths in which (nonlethal) fin ray age could be accurately corrected to (lethal) otolith age. Thin-sectioned otoliths are the gold standard for aging most fishes, including numerous age-validated catostomids, and the credibility of Blue Sucker otolith age estimates was additionally supported by a strong correlation between whole lapillus mass and estimated age (R ² = 0.89). Overall, evidence indicates that Blue Sucker lapillus otoliths yield more precise and credible age estimates than other hard structures.