Quantifying Some of the Major Sources of Uncertainty Associated with Estimates of Harp Seal Prey Consumption. Part II:Uncertainty in Consumption Estimates Associated with Population Size, Residency, Energy Requirement and Diet.

Prey consumption by Northwest Atlantic harp seals, Phoca groenlandica, depends on population size, seasonal and spatial distribution, energy requirements, energy content of prey and diet composition. There is uncertainty in our knowledge of all these components. This carries through into uncertainty in any estimate of prey consumption. Available information ranges from sample estimates, sometimes with conventional measures of precision (standard errors), to guesses based on unquantified observation. An attempt is made here to quantify the effect of some of the major sources of uncertainty, particularly with respect to the amount of Atlantic cod (Gadus morhua) eaten in NAFO Division 2J and 3KL (off southern Labrador and northeast Newfoundland). The primary objective is to determine which components contribute most to the uncertainty, as a guide for research planning. However, a thorough quantification of uncertainty would also be useful in evaluating alternative management options for harp seals which have the objective of reducing possible impacts on prey. This work examines the effect on consumption estimates of uncertainty associated with the harp seal populatoin size as well as the effect of additional sources of uncertainty attributable to residency of harp seals, energy requirements, species composition of the diet in the inshore and offshore, and the calorific value of prey.