A Bayesian approach for estimating eastern North Pacific gray whale calf production
Joshua D. Stewart and David W. Weller
International Whaling Commission
Since 1994, surveys of eastern North Pacific gray whales making their northbound migration have been conducted annually from the Piedras Blancas Light Station, in central California. Counts of mother-calf pairs by land-based observer teams have formed the basis of estimates of calf production in the population. Estimates of total calf production were previously calculated based on detection probability, which was estimated using replicate counts from two observer teams during seven consecutive years, and corrections for sightings per unit effort during a given watch period and total effort hours over the study period. Here, we introduce a new estimation method based on a Bayesian model that formally
accounts for the uncertainty associated with unsampled periods, and the differences in weekly passage rates of whales throughout the migration. This new approach resulted in slightly higher estimates of calf production across all years compared with the previous approach.