Application of computer sampling in the estimation of seal diet

The diet of seals is often estimated using the remains of otoliths found in their faeces. The fish weight of a given species is estimated from the partially digested otolith thickness, using empirically derived relationships and digestion coefficients. Errors of estimation arise from natural variation in the amount of fish represented in each faeces sample and measurement errors in estimating the fish weight from the partially digested otoliths. Computer sampling is used to estimate the bias and variance of the estimates, and to calculate the confidence intervals. The method is applied to data from samples of grey seal faeces in four study areas in different seasons.