Home ranges and movement patterns of the marine tucuxi dolphin, <i>Sotalia fluviatilis</i>, in Baía Norte, southern Brazil

Abstract

Marine tucuxi dolphins (Sotalia fluviatilis) studied in Baía Norte, southern Brazil, exhibited very small overall home ranges with daylight movements in consistent water depths of around 3m. Mean overall home range areas calculated through two methodologies were similar, measuring 13.38km² ± 1.92 using the Minimum Convex Polygon method and 15.22km² ± 0.66 through the kernel estimator. Mean core areas calculated by kernel were extremely small [mean = 1.49km² at 50% UD (utilization distribution) and 0.87km² at 25% UD levels]. The geographical distributions of home ranges and core areas overlapped extensively at both 50% UD and 25% UD. Daylight movements ranged from 0.16 to 28.97 km/day (mean = 5.65 ± 0.56km/day, SD = 5.36) with mean minimum rate of movement of 2.6 ± 0.2km/h (SD = 2.02). Daylight movement patterns varied seasonally with higher values of distance moved and rate of movement in winter and winter and autumn, respectively. The marine tucuxi home ranges and daylight movement patterns presented here are smaller than much of what is known for other coastal small cetaceans. The percentage of overall home range within the limits of a protected area designated for the tucuxis could be considered moderate to high depending on the estimator used (54.06% or 5.9km² by MCP and 74.71% or 11.35km² using the kernel). Nevertheless, core areas are completely within the protected area. Conservation implications of these findings include the need to: (i) create a buffer zone to the south of the existing protected area which will encompass the overall home range of the tucuxis; (ii) establish constant, adequate enforcement of fishery and boat traffic regulations in the core areas; and (iii) regulate boat traffic and aquaculture farming in important areas which are not yet subject to specific regulations.