Population size of humpback whale, Megaptera novaeangliae, in waters off the Pacific coast of Mexico

Abstract

The humpback whale (Megaptera novaeangliae) is a cosmo- politan species whose stocks were dras- tically decreased by commercial whal- ing practices prior to 1967. The North Pacific population was estimated to be between 15,000 and 20,000 animals before the practice of whaling. At the time of the commencement of its inter- national protection in 1967, this popu- lation may have been reduced to fewer than 1000 individuals. The Pacific coast of Mexico and the Revillagigedo Archi- pelago constitute one of the main breed- ing and calving areas for North Pacific humpback whales. The objective of this paper is to present an estimation of abundance of humpback whales in this region based on photographic identifi- cation of individual animals. Estimates of population size were obtained by us- ing mark and recapture models for both closed and open populations, with each year representing a capture occasion. A total of 1184 humpback whales were identified in Mexican waters between 1986 and 1993. The best estimates of population size for the Mexican stocks were those provided by the modified Jolly-Seber method: 1813 (95% CI: 918- 2505) for the coastal stock in 1992, and 914 (95% CI: 590-1193) for the Revil- lagigedo stock in 1991.