Surveys were conducted from aircraft over waters off the coasts of Louisiana, Mississippi, and Alabama during the summers of 1974 and 1975 to evaluate field procedures and analytical techniques for estimating population densities of bottlenosed dolphins (Tursiops truncatus). Samples using a strip proved more reliable than those based on a quadrat. Line-transect estimates were generally not feasible because the observed distribution of distances from the flight line was different from the theoretical distribution required. Differences in counts between observer teams were significant. Based on strip censuses, the following population estimates were obtained: western Louisiana (1975), 897 _ 461; Mississippi, Chandeleur and Breton sounds, marshlands habitats (1974) 438 ?+ 294; and Mississippi Sound 1,342 __ 847 (1974) and 879 ? 368 (1975). The diffe ences in the l st 2 estimates reflect the large variability inherent in the population and in the estimation procedure and are not indicative of population fluctuation. Suggestions are made for future censuses of dolphins inhabiting inshore waters. J. WILDL. MANAGE. 42(2):239-250 Since 1914, when live Atlantic bottlenosed dolphins were first displayed publicly (Townsend 1914), this species has been the mainstay of displays and shows at zoos, aquaria, and marine parks around the world, and the cetacean species most frequently maintained and studied by research institutions. Despite this familiarity with captive dolphins, there have been few studies of the species in its natural environment and the sizes of wild populations are not known. The status of knowledge was summarized by Caldwell and Caldwell (1972) and Mitchell (1975). Aerial surveys have been used in recent years to assess relative abundance of cetaceans (Gilmore and Ewing 1954, Gilmore 1960, Doan and Douglas 1953, Hubbs and Hubbs 1967, Kasuya 1971, Rice and Wolman 1971, Leatherwood 1974, Sund and O'Connor 1974, Rice 1974, Evans 1975, Leatherwood and Walker 1977). Although results of many of these studies were used to compute indices of abundance, none of the studies were designed specifically to assess the size of a population. If uit ble field techniques for collecting and statistical tools for treating data from aerial surveys for small cetaceans inhabiting inshore waters can be developed, reliable population estimates could be obtained. (Large whales and widely distribut d pelagic dolphins appear to pose a different problem.) Aerial surveys allow rapid coverage of an area at considerably less expense than shipboard surveys. Furthermore, detailed observations of natural behavior not possible from surface platforms could be made from aircraft (Leatherwood 1975, Leatherwood and Wa ker 1977). By utilizing 3 census designs, each of which was developed on the basis of prior experience, this study attempted to develop techniques for censusing bottlenosed dolphins by means of aerial transects. The specific objectives were to develop field techniques for each census method, to identify the method that would produce the most reliable population estimate, and to find reasons for the variation inherent in such estimates. We hoped ' Present address: School of Forest Resources, University,of Maine, Orono 04473. J. Wildl. Manage. 42(2):1978 239 This content downloaded from 207.46.13.120 on Wed, 14 Sep 2016 05:41:39 UTC All use subject to http://about.jstor.org/terms 240 AERIAL CENSUS OF DOLPHINS -Leatherwood et al.