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.
Highlights
Tucuxi dolphins, Sotalia fluviatilis, are endemic to South and Central America with two recognised ecotypes or species (Monteiro-Filho et al, 2002)
During 1087.5 hours of observation, S. fluviatilis was sighted on 119 occasions for a total of 75.3 hours
Bottlenose dolphins were seen on only 16 occasions and were not considered in the analyses
Summary
Sotalia fluviatilis, are endemic to South and Central America with two recognised ecotypes (da Silva and Best, 1994) or species (Monteiro-Filho et al, 2002). In 1994 the Omacha Foundation started a project to investigate the ecology of dolphin populations in the Morrosquillo Gulf, Colombian Caribbean coast. Avila (1995) determined that the most common dolphin species was S. fluviatilis and that Cispatá Bay was important for feeding purposes. Based on his results, the Omacha Foundation Project was designed to determine the importance of Cispatá Bay for both species populations, in an area where social and economic problems lay a hard pressure on the environment. The influence of boat traffic on dolphin habitat use was preliminarily explored and other potential threats were identified
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