Reproduction of Photographically Identified Fin Whales, Balaenoptera physalus, from the Gulf of Maine

Abstract

We photographically identified 534 individual fin whales ( Balaenoptera physalus ) in the Gulf of Maine from 1980 to 1988, including 64 females and 40 young. Arrival patterns of mother-young pairs were similar to other whales within years. Individual females showed strong site fidelity to either the northern or southern Gulf of Maine, suggesting substock separation on the feeding range. Gross annual rates of reproduction (proportion of individuals that were young-of-the-year) for the Gulf of Maine ranged from 0.03 to 0.12 ( X = 0.08) among years. Greater proportions of young were observed in samples from the southern Gulf of Maine ( X = 0.12) than in the northern Gulf of Maine ( X = 0.05). Greater proportions of females also were observed in the southern Gulf of Maine ( X = 0.22) than in the northern Gulf of Maine ( X = 0.10). The average time between consecutive births was 2.71 years, which represented a crude birth rate of 0.37 young per mature female per year. We estimated a potential mean interval of birthing of 2.24 years by making some assumptions for three females with incomplete sighting histories. The overall gross annual rates of reproduction that we observed were similar to rates predicted by harvest data, but rates from the northern Gulf of Maine were less than predicted. Spatial segregation of sexes or age classes may be occurring within the Gulf of Maine.