Yates, J. R., C. J. Watkins, and M. C. Quist. 2016. Precision of hard structures used to estimate age of common carp. Northwest Science 90:195-205.
Common carp Cyprinus carpio is a widely distributed non-native cyprinid in North America that often alters water quality and fish assemblage structure outside of its native distribution. Understanding age distributions and dynamic rate functions is critical for effective management of systems influenced by common carp, but requires the use of calcified structures that are accurate, precise, and have high readability. Otoliths (i.e., asteriscus) have been validated, but their removal requires sacrificing fish. In addition, unpublished studies have noted poor readability and difficulty in estimating ages from sectioned and whole otoliths. Various non-lethal hard structures for ageing common carp have been evaluated, but a comprehensive evaluation of the precision and relative readability among widely-used hard structures is lacking for common carp. We examined age estimates obtained from asteriscus otoliths, scales, pectoral fin rays, and dorsal spines of 207 common carp from Crane Creek Reservoir and Lake Lowell in southwestern Idaho. All structures were sectioned except for scales. Between-reader precision (i.e., between two readers), readability and its relationship with precision of age estimates (i.e., confidence ratings), 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 to fin rays (PA= 51.7%; CV = 4.9) and dorsal spines (PA = 65.2%; CV = 3.0). Otoliths and scales had significantly lower mean confidence ratings assigned by readers than dorsal spines and pectoral fin rays. Furthermore, both readers displayed higher confidence in assigning ages to dorsal spines than pectoral fin rays. In general, age estimates from scales and sectioned otoliths were lower than both fin rays and dorsal spines. Between-reader analysis showed high exact and within-1 year agreement, low CV, and higher confidence ratings for sectioned dorsal spines when compared to the other structures.