The 1998 Vaquita Abudance Survey was a collaboration between the National Marine Fisheries Service and SEMARNAP’s Instituto Nacional de la Pesca (INP) of Mexico. This line-transect survey was designed to collect data to estimate the abundance of vaquita, or Gulf of California harbor porpoise. The study area was from the northern end of the Gulf of California south to about 30 degrees north latitude in waters less than 100 meters deep. This survey was conducted by the NOAA Southwest Fisheries Science Center aboard the NOAA ship David Starr Jordan for a total of 1,560 kilometers surveyed from mid-August to mid-September 1997. This dataset provides the time-date and geographical coordinates, by species/stock, of all cetaceans detected during the survey, as well as the daily and intra-daily start and end points of the line-transect survey.