A method for calculating the effect of a die-off from stranding data

A method was developed for estimating the mortality during a die-off of marine mammal species from longitudinal stranding data. A deterministic mathematical model of the stranding process was used to calculate the mortality during a die-off, The model incorporated natural and anthropogenic mortality rates, the number of stranded carcasses before, during, and after the die-off, the duration of the die-off, and detection probability of a stranded carcass. The model was applied to data for the bottlenose dolphin (Tursiops truncatus) along the Atlantic coast of the United States. The mortality rate during the epizootic of 1987 and 1988 was calculated using the model. Sensitivity analyses indicated that precise estimates of natural and anthropogenic mortality rates were important for obtaining precise additional mortality rates during the die-off. For stranding data to be useful in this model, data should be collected in a consistent manner and effort within a defined area prior to, throughout, and after a die-off. Survey effort also should be measured.