Age Validation of Freshwater Drum using Bomb Radiocarbon

Abstract.—The ages of freshwater drum Aplodinotus grunniens have typically been estimated by counting the growth increments on their scales or otoliths, but the accuracy of these estimates has not been validated. We used accelerator mass spectrometry (AMS) bomb radiocarbon dating to validate age estimates from sagittal otoliths of freshwater drum from the Lake Winnebago system, Wisconsin. The freshwater drum D14C chronology from the AMS assay closely reflects the timing and shape of other bomb radiocarbon chronologies, thus validating the accuracy of otolith growth increments to at least age 52 6 2 years. The progression of a strong 1983 year-class, which was detected every year sampled over the course of the study (1986, 2003–2007), and indices of year-class abundance calculated from trawling assessments on Lake Winnebago (1986–2007) corroborated otolith ages. Age estimate comparisons between scales, anal spines, dorsal spines, and otoliths showed scales and spines to be completely unreliable as aging structures after age 2. Freshwater drum live to very old ages relative to most other Great Lakes fishes; our oldest specimen based on an otolith age estimate was 58 years old. Estimates of fish age are the foundation for understanding and forecasting fisheries population dynamics. Accurate age estimation is critical fo