Estimating Bowhead Whale Population Size and Rate of Increase from the 1993 Census

Abstract

Abstract Estimating the population size and rate of increase of bowhead whales, Balaena mysticetus, is important because bowheads were the first species of great whale for which commerical whaling stopped and so their status indicates the recovery prospects of other great whales, and also because this information is used by the International Whaling Commission (IWC) to set the aboriginal subsistence whaling quota for Alaskan Eskimos. We describe the 1993 visual and acoustic census off Point Barrow, Alaska, which provides the best data available for estimating these quantities. We outline the definitive version of two statistical methods for estimating the population: the generalized removal method and the Bayes empirical Bayes method. The two methods give results that are close. The estimate of bowhead population size most recently accepted by the IWC Scientific Committee, 8,200 with 95% estimation interval from 7,200 to 9,400, is based on the Bayes empirical Bayes posterior distribution presented here. The Scientific Committee also accepted our estimate of the annual rate of increase of the population from 1978 to 1993. This estimate, based on the generalized removal method population estimates, is 3.2% with a 95% confidence interval (1.4%, 5.1%). This shows that bowheads are increasing at a healthy rate, indicating that stocks of great whales that have been decimated by commercial hunting can recover after it ends, even in the presence of limited aboriginal subsistence whaling.