Assessing the importance of cephalopods in the diets of marine mammals and other top predators: problems and solutions

The methodology typically used in the analysis of predator diets is subject to a range of errors and biases and these are reviewed in relation to estimating the consumption of cephalopods by top predators. Further uncertainties, relating to population size estimation, predator energy requirements and sojourn time in the study area are encountered when estimating population consumption.

We review the use of such data to predict consumption of cephalopods by certain top predators globally, in the Antarctic, the Azores and in the North Atlantic. The traditional approach is based on the derivation of "minimum" and "maximum" estimates. We illustrate an alternative approach for calculating confidence limits for estimates, based on bootstrap simulations, for sperm whales in the northern Northeast Atlantic.

While the resulting confidence limits may appear discouragingly wide, computations such as those used here are useful for showing where data are most imperfect and for setting future research priorities. Even at present, within distinctly prescribed geographic areas, where populations are well known, such modelling of species interactions may be productive. (C) 2001 Elsevier Science B.V. All rights reserved.