Abundance of minke whales (Balaenoptera acutorostrata) in the Northeast Atlantic: variability in time and space

Abstract

Regional sighting surveys with two independent observers on each vessel were conducted each year from 1996 to 2001. Northern minke whales (Balaenoptera acutorostrata) are mostly solitary animals and are only available for observation at moments when they surface to breath. Thus, a stochastic point process model is developed for how the data are generated. The hazard probability of initially sighting a whale that surfaces depends on relative spatial coordinates and on other covariates. The parameters of the model are estimated by maximum likelihood. To account for interannual variation in spatial distribution of minke whales, a random effects model is developed and estimated by comparing current and past (1989 and 1995) survey data. A simulation approach is taken to remove bias from parameter estimates and to assess the uncertainty in the results. For total abundance, the result is a log-normal confidence distribution with quantiles 107 205·exp(0.137z), i.e., an abundance estimate of 107 205 with a coefficient of variation of ≈0.14. Together with these and earlier survey data, past data on catch, mark–recapture, and satellite tracking are reviewed to elucidate distribution and migration patterns in Northeastern Atlantic minke whales.