Status and ecology of Sotalia fluviatilis in the Cayos Miskito Reserve, Nicaragua.

In March through May of 1996--98 we conducted research in the Cayos Miskito Reserve, Nicaragua to assess the status, ecology and distribution of Sotalia fluviatilis, a dolphin known from southern Brazil to Honduras. Surveys of lagoons, inlets and coastal areas were conducted and observational information collected on Sotalia activity, behavior, and other factors relating to its ecology. During surveys, 183 groups (536 individuals) were sighted (for areas with Sotalia, mean overall density = 0.593/km2, coastal areas = 0.591/km 2, inlets = 0.666/km2, and lagoons = 0.484/km 2). Overall, mean herd size was 3.1 (SD = 1. 8, range 1--15) and varied among years, but not for different months. We estimate that 48 to 55 Sotalia inhabited the portion of the Reserve we studied. Sightings of Sotalia were nonrandom (nearest-neighbor analysis); clumping of sightings indicates that some areas were preferred. In both Wauhta lagoon and Paham inlet, sightings were more frequent after 1200 h than 1200 h and before. In coastal areas, Sotalia were sighted more often within 100 m of shore (54.0%) and less often from 201--300 m (6.8%). Feeding was the predominant of five recorded activities (i.e., traveling, feeding, socializing, resting and other) based on time of sighting (70.3%) and during instantaneous sampling (56.3%). Resource distribution appears to be an important factor influencing Sotalia distribution in the Reserve