Abstract
Northern right whales (Eubalaena glacialis) were formerly abundant in the northwestern Atlantic, but by 1900 they had been hunted to near extinction. After the end of commercial whaling the population was thought to be recovering slowly; however, evidence indicates that it has been declining since about 1990 (ref. 1). There are now fewer than 300 individuals, and the species may already be functionally extinct2,3 owing to demographic stochasticity or the difficulty of females locating mates in the vast Atlantic Ocean (Allee effect4). Using a data set containing over 10,000 sightings of photographically identified individuals we estimated trends in right whale demographic parameters since 1980. Here we construct, using these estimates, matrix population models allowing us to analyse the causes of right whale imperilment. Mortality has increased, especially among mother whales, causing declines in population growth rate, life expectancy and the mean lifetime number of reproductive events between the period 1980–1995. Increased mortality of mother whales can explain the declining population size, suggesting that the population is not doomed to extinction as a result of the Allee effect. An analysis of extinction time shows that demographic stochasticity has only a small effect, but preventing the deaths of only two female right whales per year would increase the population growth rate to replacement level.
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Acknowledgements
We thank S. Kraus, A. Knowlton, P. Hamilton and the NEA for data. We also thank S. Brault, M. Hill, P. Kareiva, J.-D. Lebreton, M. Neubert, J. Nichols and the participants of the first Woods Hole Workshop on the Demography of Marine Mammals for discussions and suggestions. This project was funded by the Woods Hole Oceanographic Institution Sea Grant Program, the Rinehart Coastal Research Center, the David and Lucile Packard Foundation and The Robert W. Morse Chair.
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Fujiwara, M., Caswell, H. Demography of the endangered North Atlantic right whale. Nature 414, 537–541 (2001). https://doi.org/10.1038/35107054
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DOI: https://doi.org/10.1038/35107054
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