Quantifying Some of the Major Sources of Uncertainty Associated with Estimates of Harp Seal Prey Consumption. PartI: Uncertainty in the Estimates of Harp Seal Population Size

Abstract

An effort is made to quantify some of the major sources of uncertainty associated with estimates of harp seal (Phoca groenlandica) prey consumption, with special reference to the uncertainty in estimates of seal population size. A population dynamics model is used, the inputs for which are the annual catches at age and pregnancy rates. Two parameters, instantaneous mortality rate, and the hunting selection on the pups for years prior to the availability of pregnancy data, are estimated by non-linear least squares using available survey estimates of pup production. The uncertainty in estimates of population size is estimated by Monte Carlo methods from the estimates of sampling error in the pregnancy rates and in the survey estimates of pup production, with the catches at age assumed to be known. The uncertainty in the population estimates is dominated by the uncertainty in the survey estimates.