Age structure and longevity in North Atlantic right whales Eubalaena glacialis and their relation to reproduction

Abstract

Although there are a number of techniques for determining age in dead baleen whales, few exist for live, free-swimming animals. Photo-identification records of 374 cataloged individuals through 1996 were used to assess the age of first parturition, the age structure and the longevity of the North Atlantic fight whale Eubalaena glacialis. Nearly the entire population is identified and the majority of the whales have extensive sighting histories dating from 1980, with some earlier sightings dating as far back as 1935. The observed mean age at first parturition for females with complete sighting histories (n = 13) is 8.7 yr and the age at which whales are considered adults, based on the mean age of first observed parturition for all known-age females (n = 20), is 9 yr. Juveniles and calves constitute 26 to 31% of the population, considerably less than in other baleen whale species. One whale is at least 65 yr old, and reproductive histories of others span up to 29 yr. Although the 65 plus yr old whale is possibly reproductively senescent, her apparent lack of calving may be due to anthropogenic factors or to undocumented calvings.