Evaluation of Hard Structures Used to Estimate Age of Common Carp

Understanding age distributions and dynamic rate functions is critical for effective management of Common Carp (Cyprinus carpio) populations, but requires the use of readable hard structures that produce precise age estimates. Various non-lethal hard structures for estimating age of Common Carp have been evaluated, but a comprehensive evaluation of the precision of age estimates and relative readability among widely-used hard structures is lacking. We verified age estimates obtained from asteriscus otoliths, scales, pectoral fin rays, and dorsal fin spines of 207 Common Carp from Crane Creek Reservoir and Lake Lowell in southwestern Idaho. Between-reader precision, readability, and differences in age estimates among hard structures were evaluated. Percent agreement (PA) was lower and the coefficient of variation (CV) was higher for otoliths (PA = 18.4%; CV = 17.6) and scales (PA = 29.7%; CV = 15.4) compared with pectoral fin rays (PA= 51.7%; CV = 4.9) and dorsal fin spines (PA = 65.2%; CV = 3.0). Both readers displayed higher confidence in estimating age using dorsal fin spines than pectoral fin rays. In general, age estimates from scales and otoliths were lower than both pectoral fin rays and dorsal fin spines. Between-reader analysis showed high exact and within-1 year agreement, low CV, and higher confidence ratings for age estimates obtained from dorsal fin spines when compared with the other hard structures. Dorsal fin spines provide the most repeatable estimates of Common Carp age and annuli formed on dorsal fin spines were easily read. Thus, understanding Common Carp population age structure and growth can be achieved using dorsal fin spines.