Preliminary observations on habitat use patterns of the marine tucuxi, Sotalia fluviatilis, in Cispatá Bay, Colombian Caribbean coast

Abstract

Some aspects of the habitat use of Sotalia fluviatilis were monitored in the Cispatá Bay and adjacent coastal waters on the Atlantic coast of Colombia, from November 1996 to August 1997. Dolphins were seen on 119 occasions during 1087.5 effort hours. They were present throughout the year, but entered the bay more often during the dry season, from December to April (Χ² = 262.42, p < 0.05). Most of their time was spent feeding (54%) and travelling/feeding (23%). Travelling and travelling/feeding decreased respectively from 21% to 14%, and from 41% to 6% during the rainy season. We interpreted this change in behaviour as dolphins spending more time searching for food during the dry season. S. fluviatilis entered the bay in groups of about ten individuals (SD = 8.6) and stayed within the bay for about 81.5 minutes (SD = 57.9). Dolphin presence was significantly higher during the morning than in the afternoon (H = 11.7; p < 0.05). In general, no preferential area within the bay was observed, but a seasonal difference in time spent in different zones was detected. We suggest that habitat use patterns depend mainly on resource availability and distribution. Boat traffic was significantly higher during the tourist season (t = 4.1, p < 0.05), but dolphin presence was independent of boat traffic (Χ² = 0.002, p = 0.96). They did not avoid high traffic zones, but they changed their behaviour or the direction of movement in the presence of boats in six out of nine occasions. The main pressures on the local population of S. fluviatilis were identified as: 1) High speed boat traffic inside the bay. 2) Accidental mortality in fishing gears. 3) Indirect pressure from fisheries that have depleted the marine resources and have caused habitat degradation.