ABSTRACT: Using 2 yr of field data on the abundances of live and dead planktonic copepod nauplii and Acartia tonsa copepodites from the lower Chesapeake Bay, we evaluated the accuracy of calculated mortality rates and modeled population dynamics. Copepod mortality rates were estimated from field data both before and after correcting abundances for the occurrence of carcasses. The mortality rates changed significantly when the abundance data were corrected for carcass occurrence. Instantaneous mortality rates for nauplii varied from near 0.0 d^–1 to a maximum of 0.35 d^–1 (in August 2009), and for A. tonsa copepodites from near 0.0 d^–1 in winter to 0.5 d^–1 or higher in summer. A simple model was used to evaluate the effect of both uncorrected and corrected mortality rate estimates on A. tonsa population dynamics. Model predictions more closely matched field observations when parameterized with corrected mortality rates, indicating the importance of the abundances of live and dead organisms for field studies in zooplankton ecology. We used the same field dataset to estimate the predatory and non-predatory components of mortality. Non-predatory mortality comprised an average of 25% of total mortality for nauplii, and 12% of total mortality for A. tonsa copepodites. Predatory mortality alone was insufficient to keep the A. tonsa population in check during the growing season (from June to October), demonstrating the importance of non-predatory mortality for A. tonsa in the lower Chesapeake Bay.