Accuracy and Precision of White Sturgeon Age Estimates from Pectoral Fin Rays

Abstract

Multiple readings and recaptures of marked fish were used to estimate precision and accuracy of age estimates from cross sections of pectoral fin rays of white sturgeons Acipenser transmontanus collected in impoundments of the Columbia River. Ages ranged from 2 to 104 years but only 37% of samples were assigned the same age by two readers. Percent error in multiple readings averaged 5.9% and the coefficient of variation averaged 7.8%, indicating low precision relative to reported values for other species. An injected dosage of 25 mg oxytetracycline (OTC) per kilogram of body weight marked 216 of 220 fin ray samples for validation and did not reduce white sturgeon growth. Accuracy was improved by identifying the period of annulus formation (May–June) from the position of an OTC mark relative to translucent zones in fin ray cross sections. However, age was underestimated from counts of translucent zones formed after injection with OTC, especially for slow-growing and large fish. We conclude that age estimates were not precise or accurate and recommend development of alternative methods for aging white sturgeons to supplement the fin ray method. We urge that aging data based on the fin ray method be applied cautiously. Imprecision limits interpretation of age frequencies and relative year-class strengths. Inaccuracy results in overestimation of growth, mortality, and sustainable exploitation rates.