Survival of adult blue whales Balaenoptera musculus in the Gulf of St. Lawrence, Canada

Abstract

Blue whales in eastern Canadian waters are regarded as endangered, mainly due to the lack of knowledge on their abundance and life parameters. Here, we analysed sighting histories of 362 photo-identified blue whales in the Gulf of St. Lawrence over 24 yr to estimate, for the first time, the adult survival rate of this species. The results revealed that some whales have high site fidelity while others are only visitors to the St. Lawrence. Low sighting reliability of transient whales resulted in an age structure for which there is no obvious biological justification and led us to discard the data set with all blue whales. Based on sighting records of individuals of known sex, we consider the best estimate for adult blue whale survival to be 0.975 (95% CI 0.960 to 0.985). This estimate is likely to be biased upwards by long-term records of individuals first sighted in the 1980s and sexed from biopsy samples in the 1990s, but biased downwards by emigration from the study area. The relative magnitude of these biases is, at present, unquantifiable. Trap dependency affects the probability of capture and varies between the sexes, but no significant difference in survival was found between the sexes. © Inter-Research 2006.