This study was conducted in Mexico aboard the National Oceanographic and Atmospheric Administration (NOAA) research ship McArthur during two months in summer/fall 1995. The primary purpose of this research was to learn how to better estimate the abundance of long-diving whales during ship line-transect surveys. These whale species, including beaked whales and dwarf and pygmy sperm whales, dive for such long periods of time that there is a high probability that they will never surface within the visual range of observers searching from a moving survey vessel with 25X binoculars. The project was called CADDIS (Cetacean Acoustic Detection and Dive Interval Studies) and focused on two potential approaches to improve abundance estimates: 1) acoustic detection of diving animals, and 2) collecting dive interval data on those species to serve as a basis for a model-based abundance correction factor. The CADDIS research was conducted primarily in the southern Gulf of California, Mexico. This area was chosen for two main reasons: prior surveys showed the area to have a very high density of small long-diving whales of the genera Mesoplodon, Ziphius and Kogia (Mangels and Gerrodette 1994), and the area has consistently calm seas which enables dive intervals to be observed and accurately measured. The timing of the survey was similarly chosen as the season with the consistently lowest winds in the southern Gulf.