Impact of a change in reporting systems in the Maryland blue 3 crab fishery

12 Reported landings of the blue crab (Callinectes sapidus) in the Maryland portion of Chesapeake Bay nearly doubled starting in 1981, coincident with a change from a self-reporting system for harvesters to an interview program with a randomized selection process. A peak in relative abundance as measured by a trapping survey in the Calvert Cliffs region also occurred in 1981 and persisted for several years. We developed time series models for the effects of abundance only (here referred to as transfer function models), the effects of the reporting requirement change (intervention models), and for both factors combined, on blue crab landings. Simple transfer models with consideration only of changes in abundance could not adequately account for changes in reported landings. Intervention models accounting for the change in reporting systems resulted in a considerable improvement in model performance relative to the simple transfer function model. A substantial improvement in fit was obtained with a model that included both transfer and intervention components. We conclude that the change in reporting methodology resulted in a major change in reported landings while changes in abundance account for a significant fraction of the fluctuations around the shift due to the change in statistical systems. The methods employed here provide an objective way of quantifying the effect of the reporting requirement change. 13