Aggressive Behaviors of Adult Male Atlantic Spotted Dolphins: Making Signals Count during Intraspecific and Interspecific Conflicts

Some species exhibit behavioral plasticity by altering their aggressive behavior based on their opponent. Atlantic spotted dolphins (Stenella frontalis) and bottlenose dolphins (Tursiops truncatus) are two sympatric species resident to the northern Bahamas. We examined whether groups of adult male spotted dolphins demonstrated behavioral plasticity during two different types of aggressive interactions. We described and compared the types of aggressive behaviors used during intraspecific aggression and interspecific aggression with bottlenose dolphins. Between the years 1991-2004, twenty-two aggressive encounters (11 intraspecific (spotted only), 11 interspecific (spotted vs. bottlenose)) were behaviorally analyzed. Twenty-three specific aggressive Behavioral Events, further grouped into three Behavioral Types, were examined throughout these encounters. Similarities and differences in the use of the Behavioral Types occurred during intra- and interspecific aggression. Groups of male Atlantic spotted dolphins altered their behavior during aggressive encounters with male bottlenose dolphins. Spotted dolphins increased their use of the Pursuit Behavioral Type and did not use the Display Behavioral Type significantly more than the Contact Behavioral Type during interspecific aggression. The increased use of a more overt and energy intensive Behavioral Type, Pursuit, suggests that Atlantic spotted dolphins altered their behavior during aggressive encounters with bottlenose dolphins to compensate during fights with a larger species and/or to effectively communicate with a different species.

Individual home ranges of Tursiops truncatus and their overlap with ranges of Stenella frontalis and fishermen in Aragua, Venezuela, South Caribbean

The coast of Aragua is a home of bottlenose dolphins (BND), Atlantic spotted dolphins (ASD) and fishermen (FIS) from four towns. A photo-identification study was carried out on BND to estimate their home ranges. From 2004 to 2008, 100 field surveys were carried out along 30 km of coastline (92.12 km2). In each sighting of BND, information regarding date, time, latitude/longitude and photographs were registered (ASD and FIS were registered without photography). The data were analysed using a Geographic Information System to estimate Minimum Convex Polygon (MCP) and Fixed Kernel (FK) at 95%. The home ranges of BND were estimated for seven individuals. This included three females (29–31 sightings) with estimated areas ranging from 33.90–39.90 km2 with MCP (36.79–43.31% of the study area) and from 80.47–101.31 km2 with FK (109.97–104.26%). For the remaining four dolphins (14–20 sightings) the estimated areas ranged from 9.67–22.34 km2 (MCP), the predominant depth of these home ranges varied from 51–100 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). For the pods of ASD the estimated area ranged 75.23 km2 with MCP (81.66%) and 119.86 km2 with FK (130.11%) with predominant depths of 101–200 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). The area used by FIS ranged 93.27 km2 by MCP and 228.49 km2 by FK. Finally, the overlap area of BND, ASD and FIS ranged 24.75 km2 (26.86%). We point out this locality presents important oceanographic and ecological aspects which deserve to be the subject of application of management plans for the conservation of its habitat and species.