Estimates of the current global population size and historical trajectory for sperm whales

Abstract

Assessments of sperm whale Physeter macrocephalus abundance based on invalid analyses of whaling data are common in the literature. Modern visual surveys have produced population estimates for a total of 24 % of the sperm whale's global habitat. I corrected these assessments for whales missed on the track line and then used 3 methods to scale up to a global population. Scaling using habitat area, plots of 19th century catches and primary production produced consistent global population estimates of about 360000 whales (CV = 0.36). This is approximately 20% of the numbers reproduced in current literature from invalid whaling-based estimates. A population model, based on that used by the International Whaling Commission's Scientific Committee, and which considers uncertainty in population parameters and catch data, was used to estimate population trajectories. Results suggest that pre-whaling numbers were about 1 110 000 whales (95% CI: 672 000 to 1 512 000), and that the population was about 71% (95% CI: 52 to 100%) of its original level in 1880 as open-boat whaling drew to a close and about 32 % (95 % CI: 19 to 62 %) of its original level in 1999, 10 yr after the end of large-scale hunting. Thus, widely held views about the status of sperm whale populations need considerable revision.