Reproduction in North Atlantic right whales (Eubalaena glacialis)

Abstract

The reproductive biology of the western North Atlantic right whale population was assessed using photoidentification techniques. From 1980 to 1992, 145 calves were born to 65 identified cows. There was no detectable trend in the number of calves produced per year. Mean age at first parturition was 7.57 years. The reproductively active female pool was static at approximately 51 animals from 1987 to 1992. Gross annual reproductive rate, population growth rate, and mortality rate were estimated to be 4.5, 2.5, and 2.0%, respectively. The population size was estimated to be 295 individuals in 1992. Mean calving interval, based on 86 records, was 3.67 years, significantly longer than the South African right whale population but not different from the Argentine population. There was an indication that calving intervals may be increasing over time, though the trend was not quite statistically significant (P = 0.083). Potential causes for the reduced growth rate of this population are unknown but include anthropogenic mortality, inbreeding depression resulting in reduced fecundity, competition for food from other species, climatic changes affecting food availability, and sublethal effects of toxic contaminants.