Cooperative Fish and Wildlife Research Units Program: Hawaii
Education, Research and Technical Assistance for Managing Our Natural Resources

Evaluating the precision of age estimates generated by different readers and different calcified structures is an important part of generating reliable estimations of growth, recruitment, and mortality for fish populations. Understanding the potential loss of precision associated with using structures harvested without sacrificing individuals, such as scales or fin rays, is particularly important when working with imperiled species, such as Blue Sucker Cycleptus elongatus. We collected otoliths (lapilli), scales, and the first fin rays of the dorsal, anal, pelvic, and pectoral fins of nine Blue Sucker. Age estimates were generated from each structure by both experienced (n=5) and novice (n=4) readers. We found that independent of the structure used to generate the age estimates, the mean coefficient of variation (CV) of experienced readers was approximately 29% lower than that of novice readers. Further, the mean CV of age estimates generated from pectoral fin rays, pelvic fin rays, and scales were statistically indistinguishable and less than those of dorsal fin rays, anal fin rays, and otoliths. Anal, dorsal, and pelvic fin rays and scales underestimated age compared to otoliths, but age estimates from pectoral fin rays were comparable to those from otoliths. Skill level, structure, and fish total length were factors influencing reader precision between subsequent reads of the same aging structure from a particular fish. Using structures that can be harvested non-lethally to estimate the age of Blue Sucker can provide reliable and reproducible results, similar to those that would be expected from using of otoliths. Therefore, we recommend the use of pectoral fin rays as a non-lethal method to obtain age estimates for Blue Suckers.