Despite uncertainties about interactions between ecosystems and fisheries, the ability to adjust activity of the Antarctic krill fishery based on the state of krill-dependent predators is a recognized goal of the CCAMLR. We suggest that progress toward a feedback management approach can be made efficiently via the comparative approach. Specifically, changes due to an impact in one population can be assessed by measuring trends in the difference between the observed states of a “treatment” and a “control” population. As the states of these monitored populations change relative to each other, an impact in one population will cause the relative difference between them to change. Comparing trends in the difference between pre- and post-treatment states may provide information about the magnitude of impacts that are useful for a feedback management strategy. We use a simulation study to illustrate sensitivity to the choice of data and impact, and to suggest that useful comparisons can be made across space and across species. The results suggest that relatively minor changes in the rate of decline in treatment data or minor shifts in the mean of treatment data resulted in readily identifiable (probability ≥ 95%) differences in the relative behaviour of treatment and control populations over a short (5 yr) time horizon. Such sensitivity may prove useful for the detection of impacts in monitoring data and consequent management action.