Abstract

(…) The vaquita (Phocoena sinus) is endemic to the Gulf of California and all recent sightings have been in the northern Gulf (Silber 1990a, b) where most survey efforts for this species have been concentrated. Previous ship surveys for this species were conducted by Villa-R. (1976), Wells et al. (1981), Vidal et al. (1987), and Silber (1990s) (Table 1). Aerial surveys were also conducted by Silber (1990b) and Silber and Norris (1991). None of these surveys produced quantitative estimates of vaquita population size. We conducted an experimental aerial survey in the northern Gulf of California from 11 to 14 September 1991 to evaluate the feasibility of using aerial census methods to estimate vaquita population size. (…)