Estimates of Cetacean Abundance and Distribution in the Eastern Tropical Pacific

Abstract

Large-scale research vessel surveys were conducted annually from 1986 through 1990 by the US National Marine Fisheries Service to monitor the abundance of dolphin populations in the eastern tropical Pacific Ocean (ETP). Stratified line-transect surveys with two vessels sampled an area of 19 x 106 km2. Sightings of all cetaceans were recorded, leading to the identification of 29 species. Distribution maps are presented for all species. Data from all five surveys were pooled to give single estimates of abundance in the ETP for 24 stocks of cetaceans representing 19 species or genera. Abundance estimates totaled 9.6 million animals for all dolphin species (subfamilies Delphininae and Steninae), 292,800 for all species in the subfamily Globicephalinae, 45,300 for all species in the family Ziphiidae (beaked whales), 33,881 for all species in the superfamily Physeteroidea, representing 22,666 sperm whales and 11,215 dwarf sperm whales, and 14,431 for two species in the family Balaenopteridae (rorquals), representing 13,023 Bryde’s whales and 1,415 blue whales.