Sex-specific survival in the humpback whale Megaptera novaeangliae in the Gulf of St. Lawrence, Canada

Abstract

Sex-biased adult mortality is commonly observed in the animal kingdom. In mammals, a predominantly male-biased mortality is found in species with a polygynous mating system, while in monogamous taxa, female-biased mortality prevails. In the largest of all mammals, the Mysticeti, no sex-specific mortality has been found so far apart from that found in biased whaling data. We estimated sex-specific survival rates using an Akaike Information Criterion (AICc)-based model selection of 18 yr of mark-recapture data from a North Atlantic humpback whale feeding aggregation, the Gulf of St. Lawrence, Canada. We found a significantly higher survival rate for females (0.992; 95% CI 0.985-0.999) than for males (0.971; 0.943-0.985). Humpback whales are a typical polygynous species, with males competing intensively for mates while females bear the costs of pregnancy and lactation. However, the existing data did not allow us to test if differential costs of reproduction are causing the skew in mortality. We could not preclude stock-specific differences, such as contamination levels, migratory distances, and reproductive parameters (e.g. calving intervals, age at sexual maturity), and further data are needed to investigate the underlying reasons. © Inter-Research 2010.